Science.gov

Sample records for accretion disc sad

  1. 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.

  2. Black hole accretion disc impacts

    NASA Astrophysics Data System (ADS)

    Pihajoki, P.

    2016-04-01

    We present an analytic model for computing the luminosity and spectral evolution of flares caused by a supermassive black hole impacting the accretion disc of another supermassive black hole. Our model includes photon diffusion, emission from optically thin regions and relativistic corrections to the observed spectrum and time-scales. We test the observability of the impact scenario with a simulated population of quasars hosting supermassive black hole binaries. The results indicate that for a moderate binary mass ratio of 0.3, and impact distances of 100 primary Schwarzschild radii, the accretion disc impacts can be expected to equal or exceed the host quasar in brightness at observed wavelength λ = 510 nm up to z = 0.6. We conclude that accretion disc impacts may function as an independent probe for supermassive black hole binaries. We release the code used for computing the model light curves to the community.

  3. Theory of Black Hole Accretion Discs

    NASA Astrophysics Data System (ADS)

    Abramowicz, Marek A.; Björnsson, Gunnlaugur; Pringle, James E.

    1999-03-01

    Part I. Observations of Black Holes: 1. Black holes in our Galaxy: observations P. Charles; 2. Black holes in Active Galactic Nuclei: observations G. M. Madejski; Part II. Physics Close to a Black Hole: 3. Physics of black holes I. D. Novikov; 4. Physics of black hole accretion M. A. Abramowicz; Part III. Turbulence, Viscosity: 5. Disc turbulence and viscosity A. Brandenburg; Part IV. Radiative Processes: 6. The role of electron-positron pairs in accretion flows G. Björnsson; 7. Accretion disc-corona models and X/Y-ray spectra of accreting black holes J. Poutanen; 8. Emission lines: signatures of relativistic rotation A. C. Fabian; Part V. Accretion Discs: 9. Spectral tests of models for accretion disks around black holes J. H. Krolik; 10. Advection-dominated accretion around black holes R. Narayan, R. Mahadevan and E. Quataert; 11. Accretion disc instabilities and advection dominated accretion flows J.-P. Lasota; 12. Magnetic field and multi-phase gas in AGN A. Celotti and M. J. Rees; Part V. Discs in Binary Black Holes: 13. Supermassive binary black holes in galaxies P. Artymowicz; Part VI. Stability of Accretion Discs: 14. Large scale perturbation of an accretion disc by a black hole binary companion J. C. B. Papaloizou, C. Terquem and D. N. C. Lin; 15. Stable oscillations of black hole accretion discs M. Nowak and D. Lehr; Part VI. Coherant Structures: 16. Spotted discs A. Bracco, A. Provenzale, E. A. Spiegel and P. Yecko; Self-organized critically in accretion discs P. Wiita and Y. Xiong; Summary: old and new advances in black hole accretion disc theory R. Svensson.

  4. Theory of Black Hole Accretion Discs

    NASA Astrophysics Data System (ADS)

    Abramowicz, Marek A.; Björnsson, Gunnlaugur; Pringle, James E.

    2010-08-01

    Part I. Observations of Black Holes: 1. Black holes in our Galaxy: observations P. Charles; 2. Black holes in Active Galactic Nuclei: observations G. M. Madejski; Part II. Physics Close to a Black Hole: 3. Physics of black holes I. D. Novikov; 4. Physics of black hole accretion M. A. Abramowicz; Part III. Turbulence, Viscosity: 5. Disc turbulence and viscosity A. Brandenburg; Part IV. Radiative Processes: 6. The role of electron-positron pairs in accretion flows G. Björnsson; 7. Accretion disc-corona models and X/Y-ray spectra of accreting black holes J. Poutanen; 8. Emission lines: signatures of relativistic rotation A. C. Fabian; Part V. Accretion Discs: 9. Spectral tests of models for accretion disks around black holes J. H. Krolik; 10. Advection-dominated accretion around black holes R. Narayan, R. Mahadevan and E. Quataert; 11. Accretion disc instabilities and advection dominated accretion flows J.-P. Lasota; 12. Magnetic field and multi-phase gas in AGN A. Celotti and M. J. Rees; Part V. Discs in Binary Black Holes: 13. Supermassive binary black holes in galaxies P. Artymowicz; Part VI. Stability of Accretion Discs: 14. Large scale perturbation of an accretion disc by a black hole binary companion J. C. B. Papaloizou, C. Terquem and D. N. C. Lin; 15. Stable oscillations of black hole accretion discs M. Nowak and D. Lehr; Part VI. Coherant Structures: 16. Spotted discs A. Bracco, A. Provenzale, E. A. Spiegel and P. Yecko; Self-organized critically in accretion discs P. Wiita and Y. Xiong; Summary: old and new advances in black hole accretion disc theory R. Svensson.

  5. Strongly magnetized accretion discs require poloidal flux

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    Motivated by indirect observational evidence for strongly magnetized accretion discs around black holes, and the novel theoretical properties of such solutions, we investigate how a strong magnetization state can develop and persist. To this end, we perform local simulations of accretion discs with an initially purely toroidal magnetic field of equipartition strength. We demonstrate that discs with zero net vertical magnetic flux and realistic boundary conditions cannot sustain a strong toroidal field. However, a magnetic pressure-dominated disc can form from an initial configuration with a sufficient amount of net vertical flux and realistic boundary conditions. Our results suggest that poloidal flux is a necessary prerequisite for the sustainability of strongly magnetized accretion discs.

  6. 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

  7. 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

  8. Particle rings and astrophysical accretion discs

    NASA Astrophysics Data System (ADS)

    Lovelace, R. V. E.; Romanova, M. M.

    2016-03-01

    Norman Rostoker had a wide range of interests and significant impact on the plasma physics research at Cornell during the time he was a Cornell professor. His interests ranged from the theory of energetic electron and ion beams and strong particle rings to the related topics of astrophysical accretion discs. We outline some of the topics related to rings and discs including the Rossby wave instability which leads to formation of anticyclonic vortices in astrophysical discs. These vorticies are regions of high pressure and act to trap dust particles which in turn may facilitate planetesimals growth in proto-planetary disks and could be important for planet formation. Analytical methods and global 3D magneto-hydrodynamic simulations have led to rapid advances in our understanding of discs in recent years.

  9. Disc accretion in star forming regions

    NASA Astrophysics Data System (ADS)

    Kalari, V. M.

    2015-05-01

    In this thesis, I present new ultraviolet/optical/infrared photometric and spectroscopic observations of pre-main sequence stars that have formed in either metal-poor conditions, or in the vicinity of strong ionising radiation. This includes observations of 235 Classical T Tauri stars in the Lagoon Nebula; 63 Classical T Tauri/Herbig Ae stars in the Carina Nebula open cluster Trumpler 14; 24 intermediate mass T Tauri stars in the low-Z Sh 2-284 SFR; and one Herbig B[e] PMS candidate in the metal-poor 30 Doradus SFR. I measure the accretion rates of these PMS stars using the intensities of the U/Hα band excess measured through either optical spectra or imaging. Where possible, I use archive infrared photometry in the 1.2-8 micron wavelength range to measure the PMS disc evolutionary stage. The influence of the surrounding environment on the accretion rate evolution of pre-main sequence stars in these regions is explored using the spatial, and temporal distributions of accretion rate, mass, age and disc stage of PMS stars.

  10. Accretion disc origin of the Earth's water.

    PubMed

    Vattuone, Luca; Smerieri, Marco; Savio, Letizia; Asaduzzaman, Abu Md; Muralidharan, Krishna; Drake, Michael J; Rocca, Mario

    2013-07-13

    Earth's water is conventionally believed to be delivered by comets or wet asteroids after the Earth formed. However, their elemental and isotopic properties are inconsistent with those of the Earth. It was thus proposed that water was introduced by adsorption onto grains in the accretion disc prior to planetary growth, with bonding energies so high as to be stable under high-temperature conditions. Here, we show both by laboratory experiments and numerical simulations that water adsorbs dissociatively on the olivine {100} surface at the temperature (approx. 500-1500 K) and water pressure (approx. 10⁻⁸ bar) expected for the accretion disc, leaving an OH adlayer that is stable at least up to 900 K. This may result in the formation of many Earth oceans, provided that a viable mechanism to produce water from hydroxyl exists. This adsorption process must occur in all disc environments around young stars. The inevitable conclusion is that water should be prevalent on terrestrial planets in the habitable zone around other stars. PMID:23734050

  11. Accretion disc origin of the Earth's water.

    PubMed

    Vattuone, Luca; Smerieri, Marco; Savio, Letizia; Asaduzzaman, Abu Md; Muralidharan, Krishna; Drake, Michael J; Rocca, Mario

    2013-07-13

    Earth's water is conventionally believed to be delivered by comets or wet asteroids after the Earth formed. However, their elemental and isotopic properties are inconsistent with those of the Earth. It was thus proposed that water was introduced by adsorption onto grains in the accretion disc prior to planetary growth, with bonding energies so high as to be stable under high-temperature conditions. Here, we show both by laboratory experiments and numerical simulations that water adsorbs dissociatively on the olivine {100} surface at the temperature (approx. 500-1500 K) and water pressure (approx. 10⁻⁸ bar) expected for the accretion disc, leaving an OH adlayer that is stable at least up to 900 K. This may result in the formation of many Earth oceans, provided that a viable mechanism to produce water from hydroxyl exists. This adsorption process must occur in all disc environments around young stars. The inevitable conclusion is that water should be prevalent on terrestrial planets in the habitable zone around other stars.

  12. Tearing up a misaligned accretion disc with a binary companion

    NASA Astrophysics Data System (ADS)

    Doğan, Suzan; Nixon, Chris; King, Andrew; Price, Daniel J.

    2015-05-01

    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. We calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. For typical parameters precession wins: the disc breaks into distinct planes that precess effectively independently. We run hydrodynamical simulations to check these results, and confirm that disc breaking is widespread and generally enhances accretion on to the central object. This applies in many cases of astrophysical accretion, e.g. supermassive black hole binaries and X-ray binaries.

  13. Bulk Comptonization by turbulence in accretion discs

    NASA Astrophysics Data System (ADS)

    Kaufman, J.; Blaes, O. M.

    2016-06-01

    Radiation pressure dominated accretion discs around compact objects may have turbulent velocities that greatly exceed the electron thermal velocities within the disc. Bulk Comptonization by the turbulence may therefore dominate over thermal Comptonization in determining the emergent spectrum. Bulk Comptonization by divergenceless turbulence is due to radiation viscous dissipation only. It can be treated as thermal Comptonization by solving the Kompaneets equation with an equivalent `wave' temperature, which is a weighted sum over the power present at each scale in the turbulent cascade. Bulk Comptonization by turbulence with non-zero divergence is due to both pressure work and radiation viscous dissipation. Pressure work has negligible effect on photon spectra in the limit of optically thin turbulence, and in this limit radiation viscous dissipation alone can be treated as thermal Comptonization with a temperature equivalent to the full turbulent power. In the limit of extremely optically thick turbulence, radiation viscous dissipation is suppressed, and the evolution of local photon spectra can be understood in terms of compression and expansion of the strongly coupled photon and gas fluids. We discuss the consequences of these effects for self-consistently resolving and interpreting turbulent Comptonization in spectral calculations in radiation magnetohydrodynamic simulations of high luminosity accretion flows.

  14. 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

  15. Magnetic flux stabilizing thin accretion discs

    NASA Astrophysics Data System (ADS)

    Sądowski, Aleksander

    2016-10-01

    We calculate the minimal amount of large-scale poloidal magnetic field that has to thread the inner, radiation-over-gas pressure dominated region of a thin disc for its thermal stability. Such a net field amplifies the magnetization of the saturated turbulent state and makes it locally stable. For a 10 M⊙ black hole the minimal magnetic flux is 10^{24}(dot{M}/dot{M}_Edd)^{20/21} G cm2. This amount is compared with the amount of uniform magnetic flux that can be provided by the companion star - estimated to be in the range 1022-1024 G cm2. If accretion rate is large enough, the companion is not able to provide the required amount and such a system, if still sub-Eddington, must be thermally unstable. The peculiar variability of GRS 1915+105, an X-ray binary with the exceptionally high BH mass and near-Eddington luminosity, may result from the shortage of large-scale poloidal field of uniform polarity.

  16. Super-Eddington slim accretion discs with winds

    NASA Astrophysics Data System (ADS)

    Dotan, Calanit; Shaviv, Nir J.

    2011-05-01

    We construct Super-Eddington Slim discs models around both stellar and supermassive black holes by allowing the formation of a porous layer with a reduced effective opacity. Unlike the standard scenario in which the discs become thick, super-Eddington discs remain slim. In addition, they accelerate a significant wind with a 'thick disc' geometry. We show that above about 1.5 times the standard critical mass accretion rate (needed to release the Eddington luminosity), the net luminosity released is above Eddington. At above about five times the standard critical rate, the central BH accretes more than the Eddington accretion rate. Above about ?, the disc remains slim but the wind becomes spherical, and the present model breaks down.

  17. Black hole accretion discs and screened scalar hair

    NASA Astrophysics Data System (ADS)

    Davis, Anne-Christine; Gregory, Ruth; Jha, Rahul

    2016-10-01

    We present a novel way to investigate scalar field profiles around black holes with an accretion disc for a range of models where the Compton wavelength of the scalar is large compared to other length scales. By analysing the problem in ``Weyl" coordinates, we are able to calculate the scalar profiles for accretion discs in the static Schwarzschild, as well as rotating Kerr, black holes. We comment on observational effects.

  18. Accretion of the Moon from non-canonical discs.

    PubMed

    Salmon, J; Canup, R M

    2014-09-13

    Impacts that leave the Earth-Moon system with a large excess in angular momentum have recently been advocated as a means of generating a protolunar disc with a composition that is nearly identical to that of the Earth's mantle. We here investigate the accretion of the Moon from discs generated by such 'non-canonical' impacts, which are typically more compact than discs produced by canonical impacts and have a higher fraction of their mass initially located inside the Roche limit. Our model predicts a similar overall accretional history for both canonical and non-canonical discs, with the Moon forming in three consecutive steps over hundreds of years. However, we find that, to yield a lunar-mass Moon, the more compact non-canonical discs must initially be more massive than implied by prior estimates, and only a few of the discs produced by impact simulations to date appear to meet this condition. Non-canonical impacts require that capture of the Moon into the evection resonance with the Sun reduced the Earth-Moon angular momentum by a factor of 2 or more. We find that the Moon's semi-major axis at the end of its accretion is approximately 7R⊕, which is comparable to the location of the evection resonance for a post-impact Earth with a 2.5 h rotation period in the absence of a disc. Thus, the dynamics of the Moon's assembly may directly affect its ability to be captured into the resonance.

  19. 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.

  20. Migration of accreting planets in radiative discs from dynamical torques

    NASA Astrophysics Data System (ADS)

    Pierens, A.; Raymond, S. N.

    2016-11-01

    We present the results of hydrodynamical simulations of the orbital evolution of planets undergoing runaway gas accretion in radiative discs. We consider accreting disc models with constant mass flux through the disc, and where radiative cooling balances the effect of viscous heating and stellar irradiation. We assume that 20-30 M⊕ giant planet cores are formed in the region where viscous heating dominates and migrate outward under the action of a strong entropy-related corotation torque. In the case where gas accretion is neglected and for an α viscous stress parameter α = 2 × 10-3, we find evidence for strong dynamical torques in accreting discs with accretion rates {dot{M}}≳ 7× 10^{-8} M_{⊙} yr{}^{-1}. Their main effect is to increase outward migration rates by a factor of ˜2 typically. In the presence of gas accretion, however, runaway outward migration is observed with the planet passing through the zero-torque radius and the transition between the viscous heating and stellar heating dominated regimes. The ability for an accreting planet to enter a fast migration regime is found to depend strongly on the planet growth rate, but can occur for values of the mass flux through the disc of {dot{M}}≳ 5× 10^{-8} M_{⊙} yr{}^{-1}. We find that an episode of runaway outward migration can cause an accreting planet formed in the 5-10 au region to temporarily orbit at star-planet separations as large as ˜60-70 au. However, increase in the amplitude of the Lindblad torque associated with planet growth plus change in the streamline topology near the planet systematically cause the direction of migration to be reversed. Subsequent evolution corresponds to the planet migrating inward rapidly until it becomes massive enough to open a gap in the disc and migrate in the type II regime. Our results indicate that a planet can reach large orbital distances under the combined effect of dynamical torques and gas accretion, but an alternative mechanism is required to

  1. Convection in axially symmetric accretion discs with microscopic transport coefficients

    NASA Astrophysics Data System (ADS)

    Malanchev, K. L.; Postnov, K. A.; Shakura, N. I.

    2016-09-01

    The vertical structure of stationary thin accretion discs is calculated from the energy balance equation with heat generation due to microscopic ion viscosity η and electron heat conductivity κ, both depending on temperature. In the optically thin discs it is found that for the heat conductivity increasing with temperature, the vertical temperature gradient exceeds the adiabatic value at some height, suggesting convective instability in the upper disc layer. There is a critical Prandtl number, Pr = 4/9, above which a Keplerian disc become fully convective. The vertical density distribution of optically thin laminar accretion discs as found from the hydrostatic equilibrium equation cannot be generally described by a polytrope but in the case of constant viscosity and heat conductivity. In the optically thick discs with radiation heat transfer, the vertical disc structure is found to be convectively stable for both absorption dominated and scattering dominated opacities, unless a very steep dependence of the viscosity coefficient on temperature is assumed. A polytropic-like structure in this case is found for Thomson scattering dominated opacity.

  2. Limits on luminosity and mass accretion rate of a radiation-pressure-dominated accretion disc

    NASA Astrophysics Data System (ADS)

    Cao, Xinwu; Gu, Wei-Min

    2015-04-01

    There is a maximum for the gravity of a black hole in the vertical direction in the accretion disc. Outflows may probably be driven from the disc if the radiation flux of the disc is greater than a critical value corresponding to the maximal vertical gravity. We find that outflows are driven by the radiation force from the disc if the dimensionless mass accretion rate at the outer radius dot{m}_out≳ 1 (dot{m}=dot{m}/dot{m}_Edd, dot{m} is the mass accretion rate, dot{m}_Edd=L_Edd/0.1c^2, and LEdd is the Eddington luminosity). Assuming the outflow to be strong to carry away sufficient gas from the disc surface, we find that the radiation of the disc is limited by such outflows. The disc luminosity, L_disc/L_Edd∝ ln dot{m}_out, at large-dot{m}_out cases. The Eddington ratio of the disc is ˜3 for dot{m}_out˜ 100, which is significantly lower than that of a conventional slim disc without outflows (but it is comparable with that given in the study by Kawaguchi). This implies that the emission from some ultraluminous X-ray sources with highly super Eddington luminosity should be Doppler beamed, or intermediate-mass black holes are in these sources instead of stellar mass black holes. The spectra of the discs surrounding massive black holes with outflows are saturated in the high-frequency end provided dot{m}_out≳ 2. We suggest that the saturated emission can be observed to estimate the masses of the black holes accreting at high rates, such as the narrow-line Seyfert galaxies, with the model calculations. The rate of the mass accreted by the black hole always dot{m}_in˜eq dot{m}_Edd even if the mass accretion rate at the outer radius dot{m}_out≫ dot{m}_Edd, because most of the gas is removed into the outflows by the radiation force. If this is the case, the luminous quasars at high redshifts z ≳ 6 should have grown up through persistent accretion at a rate close to the Eddington rate.

  3. 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).

  4. 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

    Context. Stars are generally born in clustered stellar environments, which can affect their subsequent evolution. An example of this environmental influence can be found in globular clusters (GCs) harbouring multiple stellar populations. An evolutionary scenario in which a second (and possibly higher order) population is formed by the accretion of chemically enriched material onto the low-mass stars in the initial GC population has been suggested to explain the multiple stellar populations. The idea, dubbed early disc accretion, is that the low-mass, pre-main-sequence stars sweep up gas expelled by the more massive stars of the same generation into their protoplanetary disc as they move through the cluster core. The same process could also occur, to a lesser extent, in embedded stellar systems that are less dense. Aims: Using assumptions that represent the (dynamical) conditions in a typical GC, we investigate whether a low-mass star of 0.4 M⊙ surrounded by a protoplanetary disc can accrete a sufficient amount of enriched material to account for the observed abundances in so-called second generation GC stars. In particular, we focus on the gas-loading rate onto the disc and star, as well as on the lifetime and stability of the disc. Methods: We perform simulations at multiple resolutions with two different smoothed particle hydrodynamics codes and compare the results. Each code uses a different implementation of the artificial viscosity. Results: We find that the gas-loading rate is about a factor of two smaller than the rate based on geometric arguments, because the effective cross-section of the disc is smaller than its surface area. Furthermore, the loading rate is consistent for both codes, irrespective of resolution. Although the disc gains mass in the high-resolution runs, it loses angular momentum on a timescale of 104 yr. Two effects determine the loss of (specific) angular momentum in our simulations: (1) continuous ram pressure stripping and (2

  5. Accretion of the Moon from non-canonical discs

    PubMed Central

    Salmon, J.; Canup, R. M

    2014-01-01

    Impacts that leave the Earth–Moon system with a large excess in angular momentum have recently been advocated as a means of generating a protolunar disc with a composition that is nearly identical to that of the Earth's mantle. We here investigate the accretion of the Moon from discs generated by such ‘non-canonical’ impacts, which are typically more compact than discs produced by canonical impacts and have a higher fraction of their mass initially located inside the Roche limit. Our model predicts a similar overall accretional history for both canonical and non-canonical discs, with the Moon forming in three consecutive steps over hundreds of years. However, we find that, to yield a lunar-mass Moon, the more compact non-canonical discs must initially be more massive than implied by prior estimates, and only a few of the discs produced by impact simulations to date appear to meet this condition. Non-canonical impacts require that capture of the Moon into the evection resonance with the Sun reduced the Earth–Moon angular momentum by a factor of 2 or more. We find that the Moon's semi-major axis at the end of its accretion is approximately 7R⊕, which is comparable to the location of the evection resonance for a post-impact Earth with a 2.5 h rotation period in the absence of a disc. Thus, the dynamics of the Moon's assembly may directly affect its ability to be captured into the resonance. PMID:25114307

  6. Accretion of the Moon from non-canonical discs.

    PubMed

    Salmon, J; Canup, R M

    2014-09-13

    Impacts that leave the Earth-Moon system with a large excess in angular momentum have recently been advocated as a means of generating a protolunar disc with a composition that is nearly identical to that of the Earth's mantle. We here investigate the accretion of the Moon from discs generated by such 'non-canonical' impacts, which are typically more compact than discs produced by canonical impacts and have a higher fraction of their mass initially located inside the Roche limit. Our model predicts a similar overall accretional history for both canonical and non-canonical discs, with the Moon forming in three consecutive steps over hundreds of years. However, we find that, to yield a lunar-mass Moon, the more compact non-canonical discs must initially be more massive than implied by prior estimates, and only a few of the discs produced by impact simulations to date appear to meet this condition. Non-canonical impacts require that capture of the Moon into the evection resonance with the Sun reduced the Earth-Moon angular momentum by a factor of 2 or more. We find that the Moon's semi-major axis at the end of its accretion is approximately 7R⊕, which is comparable to the location of the evection resonance for a post-impact Earth with a 2.5 h rotation period in the absence of a disc. Thus, the dynamics of the Moon's assembly may directly affect its ability to be captured into the resonance. PMID:25114307

  7. Slim accretion discs with different viscosity prescriptions

    NASA Astrophysics Data System (ADS)

    Szuszkiewicz, Ewa

    1990-05-01

    The variability of X-ray sources powered by accretion may be connected to thermal instabilities in the innermost parts of slim disks. The time-scales of variability predicted by the theory with the standard alpha-viscosity prescription agree with those observed in a wide range of sources. The amplitudes (3-4 orders of magnitude in luiminosity) are correctly predicted for X-ray transient sources, but in general are too big for quasars, Seyferts, galactic blackhole candidates and LMXBs. It is shown that a slight modification of the viscosity prescription can offer a much better agreement with observations.

  8. 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.

  9. Retrograde binaries of massive black holes in circumbinary accretion discs

    NASA Astrophysics Data System (ADS)

    Amaro-Seoane, Pau; Maureira-Fredes, Cristián; Dotti, Massimo; Colpi, Monica

    2016-06-01

    Context. We explore the hardening of a massive black hole binary embedded in a circumbinary gas disc under a specific circumstance: when the binary and the gas are coplanar and the gas is counter-rotating. The binary has unequal mass and the interaction of the gas with the lighter secondary black hole is the main cause of the braking torque on the binary that shrinks with time. The secondary black hole, revolving in the direction opposite to the gas, experiences a drag from gas-dynamical friction and from direct accretion of part of it. Aims: In this paper, using two-dimensional (2D) hydrodynamical grid simulations we investigate the effect of changing the accretion prescriptions on the dynamics of the secondary black hole, which in turn affect the binary hardening and eccentricity evolution. Methods: We find that realistic accretion prescriptions lead to results that differ from those inferred assuming accretion of all the gas within the Roche Lobe of the secondary black hole. Results: When considering gas accretion within the gravitational influence radius of the secondary black hole (which is smaller than the Roche Lobe radius) to better describe gas inflows, the shrinking of the binary is slower. In addition, in this case, a smaller amount of accreted mass is required to reduce the binary separation by the same amount. Different accretion prescriptions result in different discs' surface densities, which alter the black hole's dynamics back. Full 3D Smoothed-particle hydrodynamics realizations of a number of representative cases, run over a shorter interval of time, validate the general trends observed in the less computationally demanding 2D simulations. Conclusions: Initially circular black hole binaries increase their eccentricity only slightly, which then oscillates around small values (<0.1) while they harden. By contrast, initially eccentric binaries become more and more eccentric. A semi-analytical model describing the black hole's dynamics under

  10. Jet launching from accretion discs in the local approximation

    NASA Astrophysics Data System (ADS)

    Ogilvie, Gordon I.

    2012-06-01

    The acceleration of an outflow along inclined magnetic field lines emanating from an accretion disc can be studied in the local approximation, as employed in the computational model known as the shearing box. By including the slow magnetosonic point within the computational domain, the rate of mass loss in the outflow can be calculated. The accretion rates of mass and magnetic flux can also be determined, although some effects of cylindrical geometry are omitted. We formulate a simple model for the study of this problem and present the results of one-dimensional numerical simulations and supporting calculations. Quasi-steady solutions are obtained for relatively strong poloidal magnetic fields for which the magnetorotational instability is suppressed. In this regime the rate of mass loss decreases extremely rapidly with increasing field strength, or with decreasing surface density or temperature. If the poloidal magnetic field in an accretion disc can locally achieve an appropriate strength and inclination, then a rapid burst of ejection may occur. For weaker fields it may be possible to study the launching process in parallel with the magnetorotational instability, but this will require three-dimensional simulations.

  11. An accurate geometric distance to the compact binary SS Cygni vindicates accretion disc theory.

    PubMed

    Miller-Jones, J C A; Sivakoff, G R; Knigge, C; Körding, E G; Templeton, M; Waagen, E O

    2013-05-24

    Dwarf novae are white dwarfs accreting matter from a nearby red dwarf companion. Their regular outbursts are explained by a thermal-viscous instability in the accretion disc, described by the disc instability model that has since been successfully extended to other accreting systems. However, the prototypical dwarf nova, SS Cygni, presents a major challenge to our understanding of accretion disc theory. At the distance of 159 ± 12 parsecs measured by the Hubble Space Telescope, it is too luminous to be undergoing the observed regular outbursts. Using very long baseline interferometric radio observations, we report an accurate, model-independent distance to SS Cygni that places the source substantially closer at 114 ± 2 parsecs. This reconciles the source behavior with our understanding of accretion disc theory in accreting compact objects.

  12. An accurate geometric distance to the compact binary SS Cygni vindicates accretion disc theory.

    PubMed

    Miller-Jones, J C A; Sivakoff, G R; Knigge, C; Körding, E G; Templeton, M; Waagen, E O

    2013-05-24

    Dwarf novae are white dwarfs accreting matter from a nearby red dwarf companion. Their regular outbursts are explained by a thermal-viscous instability in the accretion disc, described by the disc instability model that has since been successfully extended to other accreting systems. However, the prototypical dwarf nova, SS Cygni, presents a major challenge to our understanding of accretion disc theory. At the distance of 159 ± 12 parsecs measured by the Hubble Space Telescope, it is too luminous to be undergoing the observed regular outbursts. Using very long baseline interferometric radio observations, we report an accurate, model-independent distance to SS Cygni that places the source substantially closer at 114 ± 2 parsecs. This reconciles the source behavior with our understanding of accretion disc theory in accreting compact objects. PMID:23704566

  13. Accretion-disc precession in UX Ursae Majoris

    NASA Astrophysics Data System (ADS)

    de Miguel, E.; Patterson, J.; Cejudo, D.; Ulowetz, J.; Jones, J. L.; Boardman, J.; Barret, D.; Koff, R.; Stein, W.; Campbell, T.; Vanmunster, T.; Menzies, K.; Slauson, D.; Goff, W.; Roberts, G.; Morelle, E.; Dvorak, S.; Hambsch, F.-J.; Starkey, D.; Collins, D.; Costello, M.; Cook, M. J.; Oksanen, A.; Lemay, D.; Cook, L. M.; Ogmen, Y.; Richmond, M.; Kemp, J.

    2016-04-01

    We report the results of a long campaign of time series photometry on the nova-like variable UX Ursae Majoris during 2015. It spanned 150 nights, with ˜ 1800 h of coverage on 121 separate nights. The star was in its normal `high state' near magnitude V = 13, with slow waves in the light curve and eclipses every 4.72 h. Remarkably, the star also showed a nearly sinusoidal signal with a full amplitude of 0.44 mag and a period of 3.680 ± 0.007 d. We interpret this as the signature of a retrograde precession (wobble) of the accretion disc. The same period is manifest as a ±33 s wobble in the timings of mid-eclipse, indicating that the disc's centre of light moves with this period. The star also showed strong `negative superhumps' at frequencies ωorb + N and 2ωorb + N, where ωorb and N are, respectively, the orbital and precession frequencies. It is possible that these powerful signals have been present, unsuspected, throughout the more than 60 yr of previous photometric studies.

  14. Dynamo generated magnetic configurations in accretion discs and the nature of quasi-periodic oscillations in accreting binary systems

    NASA Astrophysics Data System (ADS)

    Moss, D.; Sokoloff, D.; Suleimanov, V.

    2016-04-01

    Context. Magnetic fields are important for accretion disc structure. Magnetic fields in a disc system may be transported with the accreted matter. They can be associated with either the central body and/or jet, and be fossil or dynamo excited in situ. Aims: We consider dynamo excitation of magnetic fields in accretion discs of accreting binary systems in an attempt to clarify possible configurations of dynamo generated magnetic fields. We first model the entire disc with realistic radial extent and thickness using an alpha-quenching non-linearity. We then study the simultaneous effect of feedback from the Lorentz force from the dynamo-generated field. Methods: We perform numerical simulations in the framework of a relatively simple mean-field model which allows the generation of global magnetic configurations. Results: We explore a range of possibilities for the dynamo number, and find quadrupolar-type solutions with irregular temporal oscillations that might be compared to observed rapid luminosity fluctuations. The dipolar symmetry models with Rα< 0 have lobes of strong toroidal field adjacent to the rotation axis that could be relevant to jet launching phenomena. Conclusions: We have explored and extended the solutions known for thin accretion discs.

  15. Magnetised accretion discs in Kerr spacetimes. II. Hot spots

    NASA Astrophysics Data System (ADS)

    García, Federico; Ranea-Sandoval, Ignacio F.; Johannsen, Tim

    2016-03-01

    Context. Quasi-periodic variability has been observed in a number of X-ray binaries that harbor black hole candidates. In general relativity, black holes are uniquely described by the Kerr metric and, according to the cosmic censorship conjecture, curvature singularities always have to be clothed by an event horizon. Aims: In this paper, we study the observed light curves that arise from orbiting hotspots in thin accretion discs around Kerr black holes and naked singularities, and the effect introduced by the presence of an external magnetic field. Methods: We employ a ray-tracing algorithm to calculate the light curves and power spectra of these hot spots as seen by a distant observer for uniform and dipolar magnetic field configurations, assuming a weak coupling between the magnetic field and the disc matter. Results: We show that the presence of an external dipolar magnetic field leads to potentially observable modifications of these light curves for both Kerr black holes and naked singularities, while an external uniform magnetic field has practically no effect. In particular, we demonstrate that the emission from a hotspot, which is orbiting near the innermost stable circular orbit of a naked singularity in a dipolar magnetic field, can be significantly harder than the emission of the same hotspot in the absence of this type of magnetic field. Conclusions: The comparison of our model with observational data may allow us to study the geometry of magnetic fields around compact objects and to test the cosmic censorship conjecture in conjunction with other observables, such as thermal continuum spectra and iron line profiles.

  16. TT Arietis: 1985-1999 accretion disc behaviour

    NASA Astrophysics Data System (ADS)

    Kraicheva, Z.; Stanishev, V.; Genkov, V.; Iliev, L.

    1999-11-01

    Results of a long-term (1985-1999) photometric study of the VY Scl novalike TT Ari and CCD spectroscopic observations of the star in the region of Hα are presented. Photoelectric UBV observations carried out at Rozhen and Belogradchik observatories confirmed ~ 6 years cyclical variability of the accretion disc luminosity in high state found by frequency analysis of 70 years long light curve. The data show that the color indexes vary with the same cycle length and that in the maximum of the cycle TT Ari becomes bluer. The analysis of the ``3-hour" modulations in 1995-1998 data indicates a replacement of the ~ 0 d.1340 ``negative superhump" by ~ 0 d.1492 ``positive" one in 1997. The new wave remains active for at least a year. Based on 45 runs obtained from 1987 to 1998 in U and B bands the behaviour of the ``20-min" quasi-periodic oscillations and the flickering during both ``negative" and ``positive superhumps" regimes is investigated. All runs show strong flickering activity and power spectra with a typical red noise shape. It is found that Hα profiles and the observational characteristics of the flickering are different after 1997 when the ``positive superhump" regime started. Generally, the activity of the flickering decreased by ~ 50% in 1997-1998. The autoregressive analysis suggests that the ``20-min" QPOs observed in TT Ari light curves are most probably generated by some stochastic process such as the flickering.

  17. Circum-planetary discs as bottlenecks for gas accretion onto giant planets

    NASA Astrophysics Data System (ADS)

    Rivier, G.; Crida, A.; Morbidelli, A.; Brouet, Y.

    2012-12-01

    Context. With hundreds of exoplanets detected, it is necessary to revisit giant planets accretion models to explain their mass distribution. In particular, formation of sub-jovian planets remains unclear, given the short timescale for the runaway accretion of massive atmospheres. However, gas needs to pass through a circum-planetary disc. If the latter has a low viscosity (as expected if planets form in "dead zones"), it might act as a bottleneck for gas accretion. Aims: We investigate what the minimum accretion rate is for a planet under the limit assumption that the circum-planetary disc is totally inviscid, and the transport of angular momentum occurs solely because of the gravitational perturbations from the star. Methods: To estimate the accretion rate, we present a steady-state model of an inviscid circum-planetary disc, with vertical gas inflow and external torque from the star. Hydrodynamical simulations of a circum-planetary disc were conducted in 2D, in a planetocentric frame, with the star as an external perturber in order to measure the torque exerted by the star on the disc. Results: The disc shows a two-armed spiral wave caused by stellar tides, propagating all the way in from the outer edge of the disc towards the planet. The stellar torque is small and corresponds to a doubling time for a Jupiter mass planet of the order of 5 Myr. Given the limit assumptions, this is clearly a lower bound of the real accretion rate. Conclusions: This result shows that gas accretion onto a giant planet can be regulated by circum-planetary discs. This suggests that the diversity of masses of extra-solar planets may be the result of different viscosities in these discs.

  18. 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.

  19. 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.

  20. X-ray reflection by photoionized accretion discs

    NASA Astrophysics Data System (ADS)

    Ballantyne, D. R.; Ross, R. R.; Fabian, A. C.

    2001-10-01

    Calculations of X-ray reflection spectra from ionized, optically thick material are an important tool in investigations of accretion flows surrounding compact objects. We present the results of reflection calculations that treat the relevant physics with a minimum of assumptions. The temperature and ionization structure of the top five Thomson depths of an illuminated disc are calculated while also demanding that the atmosphere is in hydrostatic equilibrium. In agreement with Nayakshin, Kazanas & Kallman, we find that there is a rapid transition from hot to cold material in the illuminated layer. However, the transition is usually not sharp, so that often we find a small but finite region in Thomson depth where there is a stable temperature zone at T~2×106K due to photoelectric heating from recombining ions. As a result, the reflection spectra often exhibit strong features from partially ionized material, including helium-like Fe K lines and edges. The reflection spectra, when added to the illuminating spectra, were fitted by the publicly available constant-density models (i.e. pexriv, pexrav and the models of Ross & Fabian). We find that owing to the highly ionized features in the spectra these models have difficulty correctly parametrizing the new reflection spectra. There is evidence for a spurious R-Γ correlation in the ASCA energy range, where R is the reflection fraction for a power-law continuum of index Γ, confirming the suggestion of Done & Nayakshin that at least part of the R-Γ correlation reported by Zdziarski, Lubiński & Smith for Seyfert galaxies and X-ray binaries might be due to ionization effects. However, large uncertainties in the fit parameters prevent confirmation of the correlation in the 3-20keV energy range. Although many of the reflection spectra show strong, ionized features, these are not typically observed in most Seyfert and quasar X-ray spectra. However, the data are not yet good enough to place constraints on the illumination

  1. Conditions for Circumstellar Disc Formation II: Effects of Initial Cloud Stability and Mass Accretion Rate

    NASA Astrophysics Data System (ADS)

    Machida, Masahiro N.; Matsumoto, Tomoaki; Inutsuka, Shu-ichiro

    2016-09-01

    Disc formation in strongly magnetized cloud cores is investigated using a three-dimensional magnetohydrodynamic simulation with a focus on the effects of the initial cloud stability and the mass accretion rate. The initial cloud stability greatly alters the disc formation process even for prestellar clouds with the same mass-to-flux ratio. A high mass accretion rate onto the disc-forming region is realized in initially unstable clouds, and a large angular momentum is introduced into the circumstellar region in a short time. The region around the protostar has both a thin infalling envelope and a weak magnetic field, which both weaken the effect of magnetic braking. The growth of the rotation-supported disc is promoted in such unstable clouds. Conversely, clouds in an initially near-equilibrium state show lower accretion rates of mass and angular momentum. The angular momentum is transported to the outer envelope before protostar formation. After protostar formation, the circumstellar region has a thick infalling envelope and a strong magnetic field that effectively brake the disc. As a result, disc formation is suppressed when the initial cloud is in a nearly stable state. The density distribution of the initial cloud also affects the disc formation process. Disc growth strongly depends on the initial conditions when the prestellar cloud has a uniform density, whereas there is no significant difference in the disc formation process in prestellar clouds with nonuniform densities.

  2. Braking down an accreting protostar: disc-locking, disc winds, stellar winds, X-winds and Magnetospheric Ejecta

    NASA Astrophysics Data System (ADS)

    Ferreira, J.

    2013-09-01

    Classical T Tauri stars are low mass young forming stars that are surrounded by a circumstellar accretion disc from which they gain mass. Despite this accretion and their own contraction that should both lead to their spin up, these stars seem to conserve instead an almost constant rotational period as long as the disc is maintained. Several scenarios have been proposed in the literature in order to explain this puzzling "disc-locking" situation: either deposition in the disc of the stellar angular momentum by the stellar magnetosphere or its ejection through winds, providing thereby an explanation of jets from Young Stellar Objects. In this lecture, these various mechanisms will be critically detailed, from the physics of the star-disc interaction to the launching of self-confined jets (disc winds, stellar winds, X-winds, conical winds). It will be shown that no simple model can account alone for the whole bulk of observational data and that "disc locking" requires a combination of some of them.

  3. 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.

  4. Suppression of the accretion rate in thin discs around binary black holes

    NASA Astrophysics Data System (ADS)

    Ragusa, Enrico; Lodato, Giuseppe; Price, Daniel J.

    2016-08-01

    We present three-dimensional Smoothed Particle Hydrodynamics (SPH) simulations investigating the dependence of the accretion rate on the disc thickness around an equal-mass, circular black hole binary system. We find that for thick/hot discs, with H/R ≳ 0.1, the binary torque does not prevent the gas from penetrating the cavity formed in the disc by the binary (in line with previous investigations). The situation drastically changes for thinner discs; in this case the mass accretion rate is suppressed, such that only a fraction (linearly dependent on H/R) of the available gas is able to flow within the cavity and accrete on to the binary. Extrapolating this result to the cold and thin accretion discs expected around supermassive black hole binary systems implies that this kind of system accretes less material than predicted so far, with consequences not only for the electromagnetic and gravitational waves emissions during the late inspiral phase but also for the recoil speed of the black hole formed after binary coalescence, thus influencing also the evolutionary path both of the binary and of the host galaxy. Our results, being scale-free, are also applicable to equal-mass, circular binaries of stellar mass black holes, such as the progenitor of the recently discovered gravitational wave source GW150914.

  5. The subcritical baroclinic instability in local accretion disc models

    NASA Astrophysics Data System (ADS)

    Lesur, G.; Papaloizou, J. C. B.

    2010-04-01

    Context. The presence of vortices in accretion discs has been debated for more than a decade. Baroclinic instabilities might be a way to generate these vortices in the presence of a radial entropy gradient. However, the nature of these instabilities is still unclear and 3D parametric instabilities can lead to the rapid destruction of these vortices. Aims: We present new results exhibiting a subcritical baroclinic instability (SBI) in local shearing box models. We describe the 2D and 3D behaviour of this instability using numerical simulations and we present a simple analytical model describing the underlying physical process. Methods: We investigate the SBI in local shearing boxes, using either the incompressible Boussinesq approximation or a fully compressible model. We explore the parameter space varying several local dimensionless parameters and we isolate the regime relevant for the SBI. 3D shearing boxes are also investigated using high resolution spectral methods to resolve both the SBI and 3D parametric instabilities. Results: A subcritical baroclinic instability is observed in flows stable for the Solberg-Hoïland criterion using local simulations. This instability is found to be a nonlinear (or subcritical) instability, which cannot be described by ordinary linear approaches. It requires a radial entropy gradient weakly unstable for the Schwartzchild criterion and a strong thermal diffusivity (or equivalently a short cooling time). In compressible simulations, the instability produces density waves which transport angular momentum outward with typically α ⪉ 3 × 10-3, the exact value depending on the background temperature profile. Finally, the instability survives in 3D, vortex cores becoming turbulent due to parametric instabilities. Conclusions: The subcritical baroclinic instability is a robust phenomenon, which can be captured using local simulations. The instability survives in 3D thanks to a balance between the 2D SBI and 3D parametric

  6. On the high-frequency spectrum of a classical accretion disc

    NASA Astrophysics Data System (ADS)

    Balbus, Steven A.

    2014-10-01

    We derive simple and explicit expressions for the high-frequency spectrum of a classical accretion disc. Both stress-free and finite stress inner boundaries are considered. A classical accretion disc spectrum with a stress-free inner boundary departs from a Wien spectrum at large ν, scaling as ν2.5 (as opposed to ν3) times the usual exponential cut-off. If there is finite stress at the inner disc boundary, the maximum disc temperature generally occurs at this edge, even at relatively modest values of the stress. In this case, the high-frequency spectrum is proportional to ν2 times the exponential cut-off. If the temperature maximum is a local hotspot, instead of an axisymmetric ring, then an interior maximum produces a ν2 prefactor while an edge maximum yields ν1.5. Because of beaming effects, these latter findings should pertain to a classical relativistic disc. The asymptotics are in general robust and independent of the detailed temperature profile, provided only that the liberated free energy of differential rotation is dissipated locally, and may prove useful beyond the strict domain of classical disc theory. As observations continue to improve with time, our findings suggest the possibility of using the high-energy spectral component of black hole candidates as a signature prediction of classical theory, as well as a diagnostic of the stress at the inner regions of an accretion disc.

  7. A two-dimensional study for cooling and self-gravitating accretion discs

    NASA Astrophysics Data System (ADS)

    Faghei, Kazem; Pak, Milad

    2014-10-01

    The importance of cooling for the structure and evolution of self-gravitating accretion discs has been confirmed through the use of direct numerical simulations. In this paper, we present a two-dimensional study for self-gravitating accretion discs, to investigate the influence of the cooling rate on the latitudinal structure of such accretion discs. The disc is cooled using a simple parametrization for the cooling function, (d e/d t)cool=- e/ t cool with e as the internal energy and t cool as the cooling timescale. The cooling timescale is in units of the dynamical timescale, t dyn[= Ω -1], is Ωt cool= β, where β is a free parameter. The mechanism of energy dissipation is assumed to be turbulent viscosity in the disc and an α-prescription is applied for the kinematic coefficient of viscosity. To study the gravitational stability of the self-gravitating disc, we use the Toomre parameter. We obtain the radial dependence of the physical variables through the use of a self-similar method and we numerically solve the equations to obtain the latitudinal dependence of the physical variables. The solutions show that the radial velocity is smaller than the Keplerian rotational velocity; however, the disc, dependent on the values of parameters α and β and only near the zone close to the equatorial plane, can rotate in a super-Keplerian manner. With the magnitude of both parameters α and β, the disc thickness increases due to the increase of the vertical pressure gradient. The dependence of the gas density on the parameters α and β indicates two zones in the accretion disc. In the first zone near the equatorial plane, the mass density decreases by increasing these parameters. However, in the second zone, the regions with higher latitude, the mass density increases with the magnitude of parameters α and β.

  8. 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⊙.

  9. Nickel-rich outflows from accretion discs formed by the accretion-induced collapse of white dwarfs

    NASA Astrophysics Data System (ADS)

    Metzger, B. D.; Piro, A. L.; Quataert, E.

    2009-07-01

    A white dwarf (WD) approaching the Chandrasekhar mass may in several circumstances undergo accretion-induced collapse (AIC) to a neutron star (NS) before a thermonuclear explosion ensues. It has generally been assumed that such an AIC does not produce a detectable supernova (SN). If, however, the progenitor WD is rapidly rotating (as may be expected due to its prior accretion), a centrifugally supported disc forms around the NS upon collapse. We calculate the subsequent evolution of this accretion disc and its nuclear composition using time-dependent height-integrated simulations with initial conditions taken from the AIC calculations of Dessart and collaborators. Soon after its formation, the disc is cooled by neutrinos and its composition is driven neutron rich (electron fraction Ye ~ 0.1) by electron captures. However, as the disc viscously spreads, it is irradiated by neutrinos from the central proto-NS, which dramatically alters its neutron-to-proton ratio. We find that electron neutrino captures increase Ye to ~0.5 by the time that weak interactions in the disc freeze out. Because the disc becomes radiatively inefficient and begins forming α-particles soon after freeze out, powerful winds blow away most of the disc's remaining mass. These Ye ~ 0.5 outflows synthesize up to a few times 10-2Msolar in 56Ni. As a result, AIC may be accompanied by a radioactively powered SN-like transient that peaks on a time-scale of ~1 d. Since few intermediate mass elements are likely synthesized, these nickel-rich explosions should be spectroscopically distinct from other SNe. The time-scale, velocity and composition of the AIC transient can be modified if the disc wind sweeps up a ~0.1Msolar remnant disc created by a WD-WD merger; such an `enshrouded' AIC may account for sub-luminous, sub-Chandrasekhar Type I SNe. Optical transient surveys such as the Panoramic Survey Telescope and Rapid Response System and the Palomar Transient Factory should detect a few AIC transients per

  10. Revealing the accretion disc corona in Mrk 335 with multi-epoch X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Keek, L.; Ballantyne, D. R.

    2016-03-01

    Active galactic nuclei host an accretion disc with an X-ray producing corona around a supermassive black hole. In bright sources, such as the Seyfert 1 galaxy Mrk 335, reflection of the coronal emission off the accretion disc has been observed. Reflection produces spectral features such as an Fe Kα emission line, which allow for properties of the inner accretion disc and the corona to be constrained. We perform a multi-epoch spectral analysis of all XMM-Newton, Suzaku, and NuSTAR observations of Mrk 335, and we optimize our fitting procedure to unveil correlations between the Eddington ratio and the spectral parameters. We find that the disc's ionization parameter correlates strongly with the Eddington ratio: the inner disc is more strongly ionized at higher flux. The slope of the correlation is less steep than previously predicted. Furthermore, the cut-off of the power-law spectrum increases in energy with the Eddington ratio, whereas the reflection fraction exhibits a decrease. We interpret this behaviour as geometrical changes of the corona as a function of the accretion rate. Below ˜10 per cent of the Eddington limit, the compact and optically thick corona is located close to the inner disc, whereas at higher accretion rates the corona is likely optically thin and extends vertically further away from the disc surface. Furthermore, we find a soft excess that consists of two components. In addition to a contribution from reflection in low ionization states, a second component is present that traces the overall flux.

  11. Spiral-driven accretion in protoplanetary discs. II. Self-similar solutions

    NASA Astrophysics Data System (ADS)

    Hennebelle, Patrick; Lesur, Geoffroy; Fromang, Sébastien

    2016-05-01

    Context. Accretion discs are ubiquitous in the Universe, and it is crucial to understand how angular momentum and mass are radially transported in these objects. Aims: Here, we study the role played by non-linear spiral patterns within hydrodynamical and non-self-gravitating accretion discs assuming that external disturbances such as infall onto the disc may trigger them. Methods: To do so, we computed self-similar solutions that describe discs in which a spiral wave propagates. These solutions present shocks and critical sonic points that were analyzed. Results: We calculated the wave structure for all allowed temperatures and for several spiral shocks. In particular, we inferred the angle of the spiral pattern, the stress it exerts on the disc, and the associated flux of mass and angular momentum as a function of temperature. We quantified the rate of angular momentum transport by means of the dimensionless α parameter. For the thickest disc we considered (corresponding to h/r values of about one-third), we found values of α as high as 0.1 that scaled with the temperature T such that α ∝ T3 / 2 ∝ (h/r)3. The spiral angle scales with the temperature as arctan(r/h). Conclusions: These solutions suggests that perturbations occurring at disc outer boundaries, such as perturbations due to infall motions, can propagate deep inside the disc and therefore should not be ignored, even when considering small radii.

  12. Infrared accretion disc mapping of the dwarf nova V2051 Ophiuchi in outburst and in quiescence

    NASA Astrophysics Data System (ADS)

    Wojcikiewicz, E.; Baptista, R.

    2014-10-01

    Dwarf novae are compact binaries where a late-type star (the secondary) fills its Roche lobe and transfers matter to a companion white dwarf (the primary) via an accretion disc. They show outbursts which recur on timescales of weeks to years, where the accretion disc brightens by factors 20 to 100 either due to a thermal-viscous instability in the disc (DI model) or to a burst of enhanced mass-transfer from the secondary (MTI model). We report time-series of fast photometry of the dwarf nova V2051 Oph in the J and H bands, obtained with the CAMIV at the 1.6 m telescope of Observatório Pico dos Dias/Brazil, during the decline of an outburst in 2005 June, and in 2008 when the object was in quiescence. We modeled the ellipsoidal variations caused by the secondary to infer its contribution to the J and H fluxes, and fitted stellar atmosphere models to find a photometric parallatic distance of d = (111± 14)pc. Front-back brightness asymmetries in J and H-band eclipse maps along the decline from the 2005 outburst suggest that the accretion disc had a non-negligible opening angle which decreased as the disc cooled down. The time evolution of the disc radial temperature distribution along the outburst decline shows a cooling wave which accelerates as is travels inwards - in contradiction to a basic prediction from the DI model.

  13. Accretion and magnetic field morphology around Class 0 stage protostellar discs

    NASA Astrophysics Data System (ADS)

    Seifried, D.; Banerjee, R.; Pudritz, R. E.; Klessen, R. S.

    2015-01-01

    We analyse simulations of turbulent, magnetized molecular cloud cores focusing on the formation of Class 0 stage protostellar discs and the physical conditions in their surroundings. We show that for a wide range of initial conditions Keplerian discs are formed in the Class 0 stage already. In particular, we show that even subsonic turbulent motions reduce the magnetic braking efficiency sufficiently in order to allow rotationally supported discs to form. We therefore suggest that already during the Class 0 stage the fraction of Keplerian discs is significantly higher than 50 per cent, consistent with recent observational trends but significantly higher than predictions based on simulations with misaligned magnetic fields, demonstrating the importance of turbulent motions for the formation of Keplerian discs. We show that the accretion of mass and angular momentum in the surroundings of protostellar discs occurs in a highly anisotropic manner, by means of a few narrow accretion channels. The magnetic field structure in the vicinity of the discs is highly disordered, revealing field reversals up to distances of 1000 au. These findings demonstrate that as soon as even mild turbulent motions are included, the classical disc formation scenario of a coherently rotating environment and a well-ordered magnetic field breaks down. Hence, it is highly questionable to assess the magnetic braking efficiency based on non-turbulent collapse simulation. We strongly suggest that, in addition to the global magnetic field properties, the small-scale accretion flow and detailed magnetic field structure have to be considered in order to assess the likelihood of Keplerian discs to be present.

  14. Self-similar evolution of self-gravitating viscous accretion discs

    NASA Astrophysics Data System (ADS)

    Illenseer, Tobias F.; Duschl, Wolfgang J.

    2015-06-01

    A new one-dimensional, dynamical model is proposed for geometrically thin, self-gravitating viscous accretion discs. The vertically integrated equations are simplified using the slow accretion limit and the monopole approximation with a time-dependent central point mass to account for self-gravity and accretion. It is shown that the system of partial differential equations can be reduced to a single non-linear advection diffusion equation which describes the time evolution of angular velocity. In order to solve the equation, three different turbulent viscosity prescriptions are considered. It is shown that for these parametrizations the differential equation allows for similarity transformations depending only on a single non-dimensional parameter. A detailed analysis of the similarity solutions reveals that this parameter is the initial power-law exponent of the angular velocity distribution at large radii. The radial dependence of the self-similar solutions is in most cases given by broken power laws. At small radii, the rotation law always becomes Keplerian with respect to the current central point mass. In the outer regions, the power-law exponent of the rotation law deviates from the Keplerian value and approaches asymptotically the value determined by the initial condition. It is shown that accretion discs with flatter rotation laws at large radii yield higher accretion rates. The methods are applied to self-gravitating accretion discs in active galactic nuclei. Fully self-gravitating discs are found to evolve faster than nearly Keplerian discs. The implications on supermassive black hole formation and Quasar evolution are discussed.

  15. Exact time-dependent solutions for the thin accretion disc equation: boundary conditions at finite radius

    NASA Astrophysics Data System (ADS)

    Tanaka, Takamitsu

    2011-01-01

    We discuss Green's function solutions of the equation for a geometrically thin, axisymmetric Keplerian accretion disc with a viscosity prescription ν∝Rn. The mathematical problem was solved by Lynden-Bell & Pringle for the special cases with boundary conditions of zero-viscous torque and zero mass flow at the disc centre. While it has been widely established that the observational appearance of astrophysical discs depends on the physical size of the central object(s), exact time-dependent solutions with boundary conditions imposed at finite radius have not been published for a general value of the power-law index n. We derive exact Green's function solutions that satisfy either a zero-torque or a zero-flux condition at a non-zero inner boundary Rin > 0, for an arbitrary initial surface density profile. Whereas the viscously dissipated power diverges at the disc centre for the previously known solutions with Rin= 0, the new solutions with Rin > 0 have finite expressions for the disc luminosity that agree, in the limit t→∞, with standard expressions for steady-state disc luminosities. The new solutions are applicable to the evolution of the innermost regions of thin accretion discs.

  16. Structure of evolving Accretion Discs and their Implications to the Formation of Planetary Cores

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Morbidelli, A.; Crida, A.; Lega, E.

    2013-10-01

    Two features in a protoplanetary disc can have profound effects on planet formation. The first feature is "pressure bumps", i.e. local maxima in the gas surface density distribution that can arise e.g. at the inner edge of the dead zone. Pressure bumps stop the inward migration of small bodies undergoing gas drag (Brauer et al., 2008), promote the onset of the streaming instability (Johansen and Youdin, 2007), help the accretion of planetary embryos by the pebble-accretion process (Lambrechts and Johansen, 2012) and stop inward type-I migration by the planet-trap mechanism (Masset et al., 2006). The second feature is "scale height bumps", that originate from opacity transitions. The regions of the disc that are shadowed, where H/r decreases with r, allow planetary cores to migrate outwards due to entropy gradient effects (Paardekooper and Mellema (2006), Baruteau and Masset (2008)), until they reach the local minimum of the H/r profile (Bitsch et al. 2013). Thus, it is important to model the existence and the location of these structures in realistic protoplanetary discs. The structure of the disc is dependent on the mass-flux (accretion rate) through the disc, which determines the evolution of the density profile. This mass-flux changes in time, as the whole disc gets accreted onto the central star. We will show using 2D hydrodynamical models how the change of the accretion rate affects the disc structure and how this will change the sweet-spots for saving planetary cores from too rapid inward migration. We will focus here on "scale height bumps" in the disc that will change the alpha-viscosity and consequently the gas surface density (as the mass-flux is constant through the disc). Therefore the formation of pressure bumps is possible, whose prominence and effects on migration will be investigated in detail. This will give important indications of where and when in the disc the cores of giant planets and thus giant planets can form.

  17. 1D accretion discs around eccentric planets: observable near-infrared variability

    NASA Astrophysics Data System (ADS)

    Dunhill, A. C.

    2015-03-01

    I present the results of 1D models of circumplanetary discs around planets on eccentric orbits. I use a classical viscous heating model to calculate emission fluxes at the wavelengths targeted by the NIRCam instrument on JWST, and compare the variability of this signal with the published NIRCam sensitivity specifications. This variability is theoretically detectable by JWST for a sufficiently viscous disc (α ˜ 10-2) around a sufficiently eccentric planet (e ˜ 0.1-0.2) and if the circumplanetary disc accretes material from its parent disc at a rate dot{M} ≳ 10^{-7} M_{⊙} yr-1. I discuss the limitations of the models used, and the implications of the result for probing the effectiveness of disc interactions for growing a planet's orbital eccentricity.

  18. Efficiency of gas cooling and accretion at the disc-corona interface

    NASA Astrophysics Data System (ADS)

    Armillotta, L.; Fraternali, F.; Marinacci, F.

    2016-11-01

    In star-forming galaxies, stellar feedback can have a dual effect on the circumgalactic medium both suppressing and stimulating gas accretion. The trigger of gas accretion can be caused by disc material ejected into the halo in the form of fountain clouds and by its interaction with the surrounding hot corona. Indeed, at the disc-corona interface, the mixing between the cold/metal-rich disc gas (T ≲ 104 K) and the hot coronal gas (T ≳ 106 K) can dramatically reduce the cooling time of a portion of the corona and produce its condensation and accretion. We studied the interaction between fountain clouds and corona in different galactic environments through parsec-scale hydrodynamical simulations, including the presence of thermal conduction, a key mechanism that influences gas condensation. Our simulations showed that the coronal gas condensation strongly depends on the galactic environment, in particular it is less efficient for increasing virial temperature/mass of the haloes where galaxies reside and it is fully ineffective for objects with virial masses larger than 1013 M⊙. This result implies that the coronal gas cools down quickly in haloes with low-intermediate virial mass (Mvir ≲ 3 × 1012 M⊙) but the ability to cool the corona decreases going from late-type to early-type disc galaxies, potentially leading to the switching off of accretion and the quenching of star formation in massive systems.

  19. Efficiency of gas cooling and accretion at the disc-corona interface

    NASA Astrophysics Data System (ADS)

    Armillotta, L.; Fraternali, F.; Marinacci, F.

    2016-08-01

    In star-forming galaxies, stellar feedback can have a dual effect on the circumgalactic medium both suppressing and stimulating gas accretion. The trigger of gas accretion can be caused by disc material ejected into the halo in the form of fountain clouds and by its interaction with the surrounding hot corona. Indeed, at the disc-corona interface, the mixing between the cold/metal-rich disc gas (T ≲ 104 K) and the hot coronal gas (T ≳ 106 K) can dramatically reduce the cooling time of a portion of the corona and produce its condensation and accretion. We studied the interaction between fountain clouds and corona in different galactic environments through parsec-scale hydrodynamical simulations, including the presence of thermal conduction, a key mechanism that influences gas condensation. Our simulations showed that the coronal gas condensation strongly depends on the galactic environment, in particular it is less efficient for increasing virial temperature/mass of the haloes where galaxies reside and it is fully ineffective for objects with virial masses larger than 1013M⊙. This result implies that the coronal gas cools down quickly in haloes with low-intermediate virial mass (Mvir ≲ 3 × 1012M⊙) but the ability to cool the corona decreases going from late-type to early-type disc galaxies, potentially leading to the switching off of accretion and the quenching of star formation in massive systems.

  20. Three-dimensional simulations of supercritical black hole accretion discs - luminosities, photon trapping and variability

    NASA Astrophysics Data System (ADS)

    Sądowski, Aleksander; Narayan, Ramesh

    2016-03-01

    We present a set of four three-dimensional, general relativistic, radiation magnetohydrodynamical simulations of black hole accretion at supercritical mass accretion rates, dot{M} > dot{M}_Edd. We use these simulations to study how disc properties are modified when we vary the black hole mass, the black hole spin, or the mass accretion rate. In the case of a non-rotating black hole, we find that the total efficiency is of the order of 3 per cent dot{M} c^2, approximately a factor of 2 less than the efficiency of a standard thin accretion disc. The radiation flux in the funnel along the axis is highly super-Eddington, but only a small fraction of the energy released by accretion escapes in this region. The bulk of the 3 per cent dot{M} c^2 of energy emerges farther out in the disc, either in the form of photospheric emission or as a wind. In the case of a black hole with a spin parameter of 0.7, we find a larger efficiency of about 8 per cent dot{M} c^2. By comparing the relative importance of advective and diffusive radiation transport, we show that photon trapping is effective near the equatorial plane. However, near the disc surface, vertical transport of radiation by diffusion dominates. We compare the properties of our fiducial three-dimensional run with those of an equivalent two-dimensional axisymmetric model with a mean-field dynamo. The latter simulation runs nearly 100 times faster than the three-dimensional simulation, and gives very similar results for time-averaged properties of the accretion flow, but does not reproduce the time-variability.

  1. Magneto centrifugal winds from accretion discs around black hole binaries

    NASA Astrophysics Data System (ADS)

    Chakravorty, S.; Petrucci, P.-O.; Ferreira, J.; Henri, G.; Belmont, R.; Clavel, M.; Corbel, S.; Rodriguez, J.; Coriat, M.; Drappeau, S.; Malzac, J.

    2016-05-01

    We want to test if self-similar magneto-hydrodynamic (MHD) accretion-ejection models can explain the observational results for accretion disk winds in BHBs. In our models, the density at the base of the outflow from the accretion disk is not a free parameter but is determined by solving the full set of dynamical MHD equations without neglecting any physical term. Different MHD solutions were generated for different values of (a) the disk aspect ratio (ǎrepsilon) and (b) the ejection efficiency (p). We generated two kinds of MHD solutions depending on the absence (cold solution) or presence (warm solution) of heating at the disk surface. The cold MHD solutions are found to be inadequate to account for winds due to their low ejection efficiency. The warm solutions can have sufficiently high values of p (\\gtrsim 0.1) which is required to explain the observed physical quantities in the wind. The heating (required at the disk surface for the warm solutions) could be due to the illumination which would be more efficient in the Soft state. We found that in the Hard state a range of ionisation parameter is thermodynamically unstable, which makes it impossible to have any wind at all, in the Hard state. Our results would suggest that a thermo-magnetic process is required to explain winds in BHBs.

  2. Bolometric luminosity black hole growth time and slim accretion discs in active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Netzer, Hagai; Trakhtenbrot, Benny

    2014-02-01

    We investigate the accretion rate, bolometric luminosity, black hole (BH) growth time and BH spin in a large active galactic nucleus (AGN) sample under the assumption that all such objects are powered via thin or slim accretion discs (ADs). We use direct estimates of the mass accretion rate, dot{M}, to show that many currently used values of Lbol and L/LEdd are either underestimated or overestimated because they are based on bolometric correction factors that are adjusted to the properties of moderately accreting AGNs and do not take into account the correct combination of BH mass, spin and accretion rate. The consistent application of AD physics to our sample of Sloan Digital Sky Survey (SDSS) AGNs leads to the following findings. (1) Even the most conservative assumption about the radiative efficiency of fast-accreting BHs shows that many of these sources must contain slim ADs. We illustrate this by estimating the fraction of such objects at various redshifts. (2) Many previously estimated BH growth times are inconsistent with the AD theory. In particular, the growth times of the fastest accreting BHs were overestimated in the past by large factors with important consequences to AGN evolution. (3) Currently used bolometric correction factors for low accretion rate very massive SDSS BHs are inconsistent with the AD theory. Applying the AD set of assumptions to such objects, combined with standard photoionization calculations of broad emission lines, leads to the conclusion that many such objects must contain fast-spinning BHs.

  3. Simulations of overstable inertial-acoustic modes in black hole accretion discs

    NASA Astrophysics Data System (ADS)

    Fu, Wen; Lai, Dong

    2013-06-01

    We present two-dimensional inviscid hydrodynamic simulations of overstable inertial-acoustic oscillation modes (p modes) in black hole accretion discs. These global spiral waves are trapped in the innermost region of the disc, and are driven overstable by wave absorption at the corotation resonance (rc) when the gradient of the background disc vortensity (vorticity divided by surface density) at rc is positive and the disc inner boundary is sufficiently reflective. Previous linear calculations have shown that the growth rates of these modes can be as high as 10 per cent of the rotation frequency at the disc inner edge. We confirm these linear growth rates and the primary disc oscillation frequencies in our simulations when the mode amplitude undergoes exponential growth. We show that the mode growth saturates when the radial velocity perturbation becomes comparable to the disc sound speed. During the saturation stage, the primary disc oscillation frequency differs only slightly (by less than a few per cent) from the linear mode frequency. Sharp features in the fluid velocity profiles at this stage suggest that the saturation results from non-linear wave steepening and shock dissipation.

  4. Corotation resonance and overstable oscillations in black hole accretion discs: general relativistic calculations

    NASA Astrophysics Data System (ADS)

    Horák, Jiří; Lai, Dong

    2013-10-01

    We study the dynamics of spiral waves and oscillation modes in relativistic rotating discs around black holes. Generalizing the Newtonian theory, we show that wave absorption can take place at the corotation resonance, where the pattern frequency of the wave matches the background disc rotation rate. We derive the general relativistic expression for the disc vortensity (vorticity divided by surface density), which governs the behaviour of density perturbation near corotation. Depending on the gradient of the generalized disc vortensity, corotational wave absorption can lead to the amplification or damping of the spiral wave. We apply our general theory of relativistic wave dynamics to calculate the non-axisymmetric inertial-acoustic modes (also called p modes) trapped in the innermost region of a black hole accretion disc. Because general relativity changes the profiles of the radial epicyclic frequency and disc vortensity near the inner disc edge close to the black hole, these p modes can become overstable under appropriate conditions. We present the numerical results of the frequencies and growth rates of p modes for various black hole spin and model disc parameters (the surface density profile and sound speed), and discuss their implications for understanding the enigmatic high-frequency quasi-periodic oscillations observed in black hole X-ray binaries.

  5. Corotational instability, magnetic resonances and global inertial-acoustic oscillations in magnetized black hole accretion discs

    NASA Astrophysics Data System (ADS)

    Fu, Wen; Lai, Dong

    2011-01-01

    Low-order, non-axisymmetric p-modes (also referred as inertial-acoustic modes) in hydrodynamic accretion discs around black holes are plausible candidates for high-frequency quasi-periodic oscillations (QPOs) observed in a number of accreting black hole systems. These modes are trapped in the innermost region of the accretion disc, and are subject to global instabilities due to wave absorption at the corotation resonance (where the wave pattern frequency ω/m equals the disc rotation rate Ω), when the fluid vortensity, ζ=κ2/(2ΩΣ) (where κ and Σ are the radial epicyclic frequency and disc surface density, respectively), has a positive gradient. We investigate the effects of disc magnetic fields on the wave absorption at corotation and the related wave super-reflection of the corotation barrier, and on the overstability of disc p-modes. In general, in the presence of magnetic fields, the p-modes have the character of inertial-fast magnetosonic waves in their propagation zone. For discs with a pure toroidal field, the corotation resonance is split into two magnetic resonances, where the wave frequency in the corotating frame of the fluid, ?, matches the slow magnetosonic wave frequency. Significant wave energy/angular momentum absorption occurs at both magnetic resonances, but with opposite signs, such that one of them enhances the super-reflection while the other diminishes it. The combined effect of the two magnetic resonances is to reduce the super-reflection and the growth rate of the overstable p-modes. Our calculations show that even a subthermal toroidal field (with the magnetic pressure less than the gas pressure) may suppress the overstability of hydrodynamic (B= 0) p-modes. For accretion discs with mixed (toroidal and vertical) magnetic fields, two additional Alfvén resonances appear, where ? matches the local Alfvén wave frequency. The effect of these additional resonances is to further reduce or diminish the growth rate of p-modes. Our results

  6. Outflows from accretion discs formed in neutron star mergers: effect of black hole spin

    NASA Astrophysics Data System (ADS)

    Fernández, Rodrigo; Kasen, Daniel; Metzger, Brian D.; Quataert, Eliot

    2015-01-01

    The accretion disc that forms after a neutron star merger is a source of neutron-rich ejecta. The ejected material contributes to a radioactively powered electromagnetic transient, with properties that depend sensitively on the composition of the outflow. Here, we investigate how the spin of the black hole (BH) remnant influences mass ejection on the thermal and viscous time-scales. We carry out two-dimensional, time-dependent hydrodynamic simulations of merger remnant accretion discs including viscous angular momentum transport and approximate neutrino self-irradiation. The gravity of the spinning BH is included via a pseudo-Newtonian potential. We find that a disc around a spinning BH ejects more mass, up to a factor of several, relative to the non-spinning case. The enhanced mass-loss is due to energy release by accretion occurring deeper in the gravitational potential, raising the disc temperature and hence the rate of viscous heating in regions where neutrino cooling is ineffective. The mean electron fraction of the outflow increases moderately with BH spin due to a highly irradiated (though not neutrino-driven) wind component. While the bulk of the ejecta is still very neutron-rich, thus generating heavy r-process elements, the leading edge of the wind contains a small amount of Lanthanide-free material. This component can give rise to an ≲1 d blue optical `bump' in a kilonova light curve, even in the case of prompt BH formation, which may facilitate its detection.

  7. A test of truncation in the accretion discs of X-ray Binaries.

    NASA Astrophysics Data System (ADS)

    Eckersall, A.

    2016-06-01

    The truncated-disc model is generally used to help explain the change between the soft and hard states in X-ray Binaries, where the standard accretion disc is truncated in the inner regions and replaced by a radiatively inefficient accretion flow. There is still disagreement though in the extent of this truncation, particularly in at what point truncation begins. Here we analyze XMM EPIC-pn spectra in both the soft and hard states for a number of galactic XRBs, along with RGS data and the latest absorption and emission models to get an independent fit for the ISM column densities for each source. Specifically, we assume the 'canonical' model where the luminous accretion disc extends down to the innermost stable orbit at 6r_g, and construct a spectral model accounting for thermal, reflection and Compton processes ensuring consistent geometrical properties of the models. Rather than attempting to infer the inner disc location from spectral fitting and/or reflection models, we instead attempt a direct test of whether a consistent model will fit assuming no truncation. We discuss the implications for emission models of XRBs.

  8. MRI channel flows in vertically stratified models of accretion discs

    NASA Astrophysics Data System (ADS)

    Latter, Henrik N.; Fromang, Sebastien; Gressel, Oliver

    2010-08-01

    Simulations of the magnetorotational instability (MRI) in `unstratified' shearing boxes exhibit powerful coherent flows, whereby the fluid vertically splits into countermoving planar jets or `channels'. Channel flows correspond to certain axisymmetric linear MRI modes, and their preponderance follows from the remarkable fact that they are approximate non-linear solutions of the MHD equations in the limit of weak magnetic fields. We show in this paper, analytically and with one-dimensional numerical simulations, that this property is also shared by certain axisymmetric MRI modes in vertically stratified shearing boxes. These channel flows rapidly capture significant amounts of magnetic and kinetic energy, and thus are vulnerable to secondary shear instabilities. We examine these parasites in the vertically stratified context, and estimate the maximum amplitudes that channels attain before they are destroyed. These estimates suggest that a dominant channel flow will usually drive the disc's magnetic field to thermal strengths. The prominence of these flows and their destruction place enormous demands on simulations, but channels in their initial stages also offer a useful check on numerical codes. These benchmarks are especially valuable given the increasing interest in the saturation of the stratified MRI. Lastly, we speculate on the potential connection between `run-away' channel flows and outburst behaviour in protostellar and dwarf nova discs.

  9. Accretion of Phobos and Deimos in an extended debris disc stirred by transient moons

    NASA Astrophysics Data System (ADS)

    Rosenblatt, Pascal; Charnoz, Sébastien; Dunseath, Kevin M.; Terao-Dunseath, Mariko; Trinh, Antony; Hyodo, Ryuki; Genda, Hidenori; Toupin, Stéven

    2016-08-01

    Phobos and Deimos, the two small satellites of Mars, are thought either to be asteroids captured by the planet or to have formed in a disc of debris surrounding Mars following a giant impact. Both scenarios, however, have been unable to account for the current Mars system. Here we use numerical simulations to suggest that Phobos and Deimos accreted from the outer portion of a debris disc formed after a giant impact on Mars. In our simulations, larger moons form from material in the denser inner disc and migrate outwards due to gravitational interactions with the disc. The resulting orbital resonances spread outwards and gather dispersed outer disc debris, facilitating accretion into two satellites of sizes similar to Phobos and Deimos. The larger inner moons fall back to Mars after about 5 million years due to the tidal pull of the planet, after which the two outer satellites evolve into Phobos- and Deimos-like orbits. The proposed scenario can explain why Mars has two small satellites instead of one large moon. Our model predicts that Phobos and Deimos are composed of a mixture of material from Mars and the impactor.

  10. Integrated accretion disc angular momentum removal and astrophysical jet acceleration mechanism

    NASA Astrophysics Data System (ADS)

    Bellan, P. M.

    2016-06-01

    Ions and neutrals in the weakly ionized plasma of an accretion disc are tightly bound because of the high ion-neutral collision frequency. A cluster of a statistically large number of ions and neutrals behaves as a fluid element having the charge of the ions and the mass of the neutrals. This fluid element is effectively a metaparticle having such an extremely small charge-to-mass ratio that its cyclotron frequency can be of the order of the Kepler angular frequency. In this case, metaparticles with a critical charge-to-mass ratio can have zero canonical angular momentum. Zero canonical angular momentum metaparticles experience no centrifugal force and spiral inwards towards the central body. Accumulation of these inward spiralling metaparticles near the central body produces radially and axially outward electric fields. The axially outward electric field drives an out-of-plane poloidal electric current along arched poloidal flux surfaces in the highly ionized volume outside the disc. This out-of-plane current and its associated magnetic field produce forces that drive bidirectional astrophysical jets flowing normal to and away from the disc. The poloidal electric current circuit removes angular momentum from the accreting mass and deposits this removed angular momentum at near infinite radius in the disc plane. The disc region is an electric power source (E\\cdot J <0) while the jet region is an electric power sink (E\\cdot J>0).

  11. HEROIC: 3D general relativistic radiative post-processor with comptonization for black hole accretion discs

    NASA Astrophysics Data System (ADS)

    Narayan, Ramesh; Zhu, Yucong; Psaltis, Dimitrios; Saḑowski, Aleksander

    2016-03-01

    We describe Hybrid Evaluator for Radiative Objects Including Comptonization (HEROIC), an upgraded version of the relativistic radiative post-processor code HERO described in a previous paper, but which now Includes Comptonization. HEROIC models Comptonization via the Kompaneets equation, using a quadratic approximation for the source function in a short characteristics radiation solver. It employs a simple form of accelerated lambda iteration to handle regions of high scattering opacity. In addition to solving for the radiation field, HEROIC also solves for the gas temperature by applying the condition of radiative equilibrium. We present benchmarks and tests of the Comptonization module in HEROIC with simple 1D and 3D scattering problems. We also test the ability of the code to handle various relativistic effects using model atmospheres and accretion flows in a black hole space-time. We present two applications of HEROIC to general relativistic magnetohydrodynamics simulations of accretion discs. One application is to a thin accretion disc around a black hole. We find that the gas below the photosphere in the multidimensional HEROIC solution is nearly isothermal, quite different from previous solutions based on 1D plane parallel atmospheres. The second application is to a geometrically thick radiation-dominated accretion disc accreting at 11 times the Eddington rate. Here, the multidimensional HEROIC solution shows that, for observers who are on axis and look down the polar funnel, the isotropic equivalent luminosity could be more than 10 times the Eddington limit, even though the spectrum might still look thermal and show no signs of relativistic beaming.

  12. A transition in circumbinary accretion discs at a binary mass ratio of 1:25

    NASA Astrophysics Data System (ADS)

    D'Orazio, Daniel J.; Haiman, Zoltán; Duffell, Paul; MacFadyen, Andrew; Farris, Brian

    2016-07-01

    We study circumbinary accretion discs in the framework of the restricted three-body problem (R3Bp) and via numerically solving the height-integrated equations of viscous hydrodynamics. Varying the mass ratio of the binary, we find a pronounced change in the behaviour of the disc near mass ratio q ≡ Ms/Mp ˜ 0.04. For mass ratios above q = 0.04, solutions for the hydrodynamic flow transition from steady, to strongly fluctuating; a narrow annular gap in the surface density around the secondary's orbit changes to a hollow central cavity; and a spatial symmetry is lost, resulting in a lopsided disc. This phase transition is coincident with the mass ratio above which stable orbits do not exist around the L4 and L5 equilibrium points of the R3Bp. Using the DISCO code, we find that for thin discs, for which a gap or cavity can remain open, the mass ratio of the transition is relatively insensitive to disc viscosity and pressure. The q = 0.04 transition has relevance for the evolution of massive black hole binary+disc systems at the centres of galactic nuclei, as well as for young stellar binaries and possibly planets around brown dwarfs.

  13. Evolution of accretion discs around a kerr black hole using extended magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Foucart, Francois; Chandra, Mani; Gammie, Charles F.; Quataert, Eliot

    2016-02-01

    Black holes accreting well below the Eddington rate are believed to have geometrically thick, optically thin, rotationally supported accretion discs in which the Coulomb mean free path is large compared to GM/c2. In such an environment, the disc evolution may differ significantly from ideal magnetohydrodynamic (MHD) predictions. We present non-ideal global axisymmetric simulations of geometrically thick discs around a rotating black hole. The simulations are carried out using a new code GRIM, which evolves a covariant extended magnetohydrodynamics model derived by treating non-ideal effects as a perturbation of ideal MHD. Non-ideal effects are modelled through heat conduction along magnetic field lines, and a difference between the pressure parallel and perpendicular to the field lines. The model relies on an effective collisionality in the disc from wave-particle scattering and velocity-space (mirror and firehose) instabilities. We find that the pressure anisotropy grows to match the magnetic pressure, at which point it saturates due to the mirror instability. The pressure anisotropy produces outward angular momentum transport with a magnitude comparable to that of MHD turbulence in the disc, and a significant increase in the temperature in the wall of the jet. We also find that, at least in our axisymmetric simulations, conduction has a small effect on the disc evolution because (1) the heat flux is constrained to be parallel to the field and the field is close to perpendicular to temperature gradients, and (2) the heat flux is choked by an increase in effective collisionality associated with the mirror instability.

  14. Modelling accretion disc and stellar wind interactions: the case of Sgr A*

    NASA Astrophysics Data System (ADS)

    Christie, I. M.; Petropoulou, M.; Mimica, P.; Giannios, D.

    2016-07-01

    Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disc, the ram and thermal pressures of the disc terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind. With the employment of numerical hydrodynamic simulations, this model is both verified and extended to a region prone to Kelvin-Helmholtz instabilities. Because the characteristic wind and stellar velocities are in ˜108 cm s-1 range, the shocked wind may produce detectable X-rays via thermal bremsstrahlung emission. The application of this model to the pericentre passage of S2, the brightest member of the S-cluster, shows that the shocked wind produces roughly a month long X-ray flare with a peak luminosity of L ≈ 4 × 1033 erg s-1 for a stellar mass-loss rate, disc number density, and thermal pressure strength of dot{M}_w= 10^{-7} M_{⊙} yr^{-1}, nd = 105 cm-3, and α = 0.1, respectively. This peak luminosity is comparable to the quiescent X-ray emission detected from Sgr A* and is within the detection capabilities of current X-ray observatories. Its detection could constrain the density and thickness of the disc at a distance of ˜3000 gravitational radii from the supermassive black hole.

  15. Infalling clouds on to supermassive black hole binaries - I. Formation of discs, accretion and gas dynamics

    NASA Astrophysics Data System (ADS)

    Goicovic, F. G.; Cuadra, J.; Sesana, A.; Stasyszyn, F.; Amaro-Seoane, P.; Tanaka, T. L.

    2016-01-01

    There is compelling evidence that most - if not all - galaxies harbour a supermassive black hole (SMBH) at their nucleus; hence binaries of these massive objects are an inevitable product of the hierarchical evolution of structures in the Universe, and represent an important but thus-far elusive phase of galaxy evolution. Gas accretion via a circumbinary disc is thought to be important for the dynamical evolution of SMBH binaries, as well as in producing luminous emission that can be used to infer their properties. One plausible source of the gaseous fuel is clumps of gas formed due to turbulence and gravitational instabilities in the interstellar medium, that later fall towards and interact with the binary. In this context, we model numerically the evolution of turbulent clouds in near-radial infall on to equal-mass SMBH binaries, using a modified version of the SPH (smoothed particle hydrodynamics) code GADGET-3. We present a total of 12 simulations that explore different possible pericentre distances and relative inclinations, and show that the formation of circumbinary discs and discs around each SMBH (`mini-discs') depend on those parameters. We also study the dynamics of the formed discs, and the variability of the feeding rate on to the SMBHs in the different configurations.

  16. Kinematics and excitation of the molecular hydrogen accretion disc in NGC 1275

    NASA Astrophysics Data System (ADS)

    Scharwächter, J.; McGregor, P. J.; Dopita, M. A.; Beck, T. L.

    2013-03-01

    We report the results of high spatial and spectral resolution integral-field spectroscopy of the central ˜3 × 3 arcsec2 of the active galaxy NGC 1275 (Perseus A), based on observations with the Near-infrared Integral Field Spectrograph (NIFS) and the ALTitude conjugate Adaptive optics for the InfraRed (ALTAIR) adaptive-optics system on the Gemini North telescope. The circum-nuclear disc in the inner R ˜ 50 pc of NGC 1275 is seen in both the H2 and [Fe II] lines. The disc is interpreted as the outer part of a collisionally excited turbulent accretion disc. The kinematic major axis of the disc at a position angle of 68° is oriented perpendicular to the radio jet. A streamer-like feature to the south-west of the disc, detected in H2 but not in [Fe II], is discussed as one of possibly several molecular streamers, presumably falling into the nuclear region. Indications of an ionization structure within the disc are deduced from the He I and Brγ emission lines, which may partially originate from the inner portions of the accretion disc. The kinematics of these two lines agrees with the signature of the circum-nuclear disc, but both lines display a larger central velocity dispersion than the H2 line. The ro-vibrational H2 transitions from the core of NGC 1275 are indicative of thermal excitation caused by shocks and agree with excitation temperatures of ˜1360 and ˜4290 K for the lower and higher energy H2 transitions, respectively. The data suggest X-ray heating as the dominant excitation mechanism of [Fe II] emission in the core, while fast shocks are a possible alternative. The [Fe II] lines indicate an electron density of ˜4000 cm-3. The H2 disc is modelled using simulated NIFS data cubes of H2 emission from inclined discs in Keplerian rotation around a central mass. Assuming a disc inclination of 45° ± 10°, the best-fitting models imply a central mass of (8 + 7 - 2) × 108 M⊙. Taken as a black hole mass estimate, this value is larger than previous

  17. X-Ray Evidence for the Accretion Disc-Outflow Connection in 3C 111

    NASA Technical Reports Server (NTRS)

    Tombesi, Frank; Sambruna, R. M.; Reeves, J. N.; Reynolds, C. S.; Braito, V.

    2011-01-01

    We present the spectral analysis of three Suzaku X-ray Imaging Spectrometer observations of 3C III requested to monitor the predicted variability of its ultrafast outflow on approximately 7 d time-scales. We detect an ionized iron emission line in the first observation and a blueshifted absorption line in the second, when the flux is approximately 30 per cent higher. The location of the material is constrained at less than 0.006 pc from the variability. Detailed modelling supports an identification with ionized reflection off the accretion disc at approximately 20-100rg from the black hole and a highly ionized and massive ultrafast outflow with velocity approximately 0.1c, respectively. The outflow is most probably accelerated by radiation pressure, but additional magnetic thrust cannot be excluded. The measured high outflow rate and mechanical energy support the claims that disc outflows may have a significant feedback role. This work provides the first direct evidence for an accretion disc-outflow connection in a radio-loud active galactic nucleus, possibly linked also to the jet activity.

  18. Variabilities of gamma-ray bursts from black hole hyper-accretion discs

    NASA Astrophysics Data System (ADS)

    Lin, Da-Bin; Lu, Zu-Jia; Mu, Hui-Jun; Liu, Tong; Hou, Shu-Jin; Lü, Jing; Gu, Wei-Min; Liang, En-Wei

    2016-11-01

    The emission from black hole binaries (BHBs) and active galactic nuclei (AGNs) display significant aperiodic variabilities. The most promising explanation for these variabilities is the propagating fluctuations in the accretion flow. It is natural to expect that the mechanism driving variabilities in BHBs and AGNs may operate in a black hole hyper-accretion disc, which is believed to power gamma-ray bursts (GRBs). We study the variabilities of jet power in GRBs based on the model of propagating fluctuations. It is found that the variabilities of jet power and the temporal profile of erratic spikes in this scenario are similar to those in observed light curves of prompt gamma-ray emission of GRBs. Our results show that the mechanism driving X-ray variabilities in BHBs and AGNs may operate in the central engine to drive the variabilities of GRBs.

  19. Local and global aspects of the linear MRI in accretion discs

    NASA Astrophysics Data System (ADS)

    Latter, Henrik N.; Fromang, Sebastien; Faure, Julien

    2015-11-01

    We revisit the linear magnetorotational instability (MRI) in a cylindrical model of an accretion disc and uncover a number of attractive results overlooked in previous treatments. In particular, we elucidate the connection between local axisymmetric modes and global modes, and show that a local channel flow corresponds to the evanescent part of a global mode. In addition, we find that the global problem reproduces the local dispersion relation without approximation, a result that helps explain the success the local analysis enjoys in predicting global growth rates. MRI channel flows are non-linear solutions to the governing equations in the local shearing box. However, only a small subset of MRI modes share the same property in global disc models, providing further evidence that the prominence of channels in local boxes is artificial. Finally, we verify our results via direct numerical simulations with the Godunov code RAMSES.

  20. Emission line eclipse mapping of velocity fields in dwarf nova accretion discs

    NASA Astrophysics Data System (ADS)

    Makita, M.; Mineshige, S.

    2002-01-01

    We propose a new method, emission-line eclipse mapping, to map the velocity fields in an accretion disc. We apply the usual eclipse mapping technique to the light curves at each of 12-24 wavelengths across the line center to map the region with same line-of-sight velocity, from which we are able to plot the rotational velocity as a function of radius on the assumption of axisymmetric disc. We calculate time changes of the emission line profiles, assuming Keplerian rotation fields (vvarphi propto r-1/2) and the emissivity distribution of j propto r-3/2, and reconstruct emissivity profiles. The results show typically a `two-eye' pattern for high line-of-sight velocities and we can recover the relation, vvarphi propto d-1/2, where d is the separation of two lq eyes.'

  1. Inertial-acoustic oscillations of black hole accretion discs with large-scale poloidal magnetic fields

    NASA Astrophysics Data System (ADS)

    Yu, Cong; Lai, Dong

    2015-07-01

    We study the effect of large-scale magnetic fields on the non-axisymmetric inertial-acoustic modes (also called p modes) trapped in the innermost regions of accretion discs around black holes (BHs). These global modes could provide an explanation for the high-frequency quasi-periodic oscillations (HFQPOs) observed in BH X-ray binaries. There may be observational evidence for the presence of such large-scale magnetic fields in the discs since episodic jets are observed in the same spectral state when HFQPOs are detected. We find that a large-scale poloidal magnetic field can enhance the corotational instability and increase the growth rate of the purely hydrodynamic overstable p modes. In addition, we show that the frequencies of these overstable p modes could be further reduced by such magnetic fields, making them agree better with observations.

  2. The main sequences of NGC 2808: constraints on the early disc accretion scenario

    NASA Astrophysics Data System (ADS)

    Cassisi, Santi; Salaris, Maurizio

    2014-03-01

    A new scenario - early disc accretion - has been proposed very recently to explain the origin of the multiple population phenomenon in Galactic globular clusters. It envisages the possibility that a fraction of low- and very low-mass cluster stars may accrete the ejecta of interacting massive binary (and possibly also fast rotating massive) stars during the fully convective, pre-main sequence stage, to reproduce the CN and ONa anticorrelations observed among stars in individual clusters. This scenario is assumed to be able to explain the presence (and properties) of the multiple populations in the majority of globular clusters in the Milky Way. Here we have considered the well studied cluster NGC 2808, which displays a triple main sequence with well defined and separate He abundances. Knowledge of these abundances allowed us to put strong constraints on the He mass fraction and amount of matter to be accreted by low-mass pre-main sequence stars. We find that the minimum He mass fraction in the accreted gas has to be ~0.44 to produce the observed sequences and that at fixed initial mass of the accreting star, different efficiencies for the accretion are required to produce stars placed onto the multiple main sequences. This may be explained by differences in the orbital properties of the progenitors and/or different spatial distribution of intracluster gas with varying He abundances. Both O-Na and C-N anticorrelations appear naturally along the main sequences, once considering the predicted relationship between He and CNONa abundances in the ejecta of the polluters. As a consequence of the accretion, we predict no discontinuity between the abundance ranges covered by intermediate and blue main sequence stars, but we find a sizeable (several 0.1 dex) discontinuity of the N and Na abundances between objects on the intermediate and red main sequences. There is in principle enough polluting gas with the right He abundances to explain the observed main sequences by early

  3. Estimation of mass outflow rates from viscous relativistic accretion discs around black holes

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, Indranil; Kumar, Rajiv

    2016-07-01

    We investigated flow in Schwarzschild metric, around a non-rotating black hole and obtained self-consistent accretion-ejection solution in full general relativity. We covered the whole of parameter space in the advective regime to obtain shocked, as well as, shock-free accretion solution. We computed the jet streamline using von Zeipel surfaces and projected the jet equations of motion on to the streamline and solved them simultaneously with the accretion disc equations of motion. We found that steady shock cannot exist beyond α ≳ 0.06 in the general relativistic prescription, but is lower if mass-loss is considered too. We showed that for fixed outer boundary, the shock moves closer to the horizon with increasing viscosity parameter. The mass outflow rate increases as the shock moves closer to the black hole, but eventually decreases, maximizing at some intermediate value of shock location. The jet terminal speed increases with stronger shocks; quantitatively speaking, the terminal speed of jets vj∞ > 0.1 if rsh < 20rg. The maximum of the outflow rate obtained in the general relativistic regime is less than 6 per cent of the mass accretion rate.

  4. Flickering of accreting white dwarfs: the remarkable amplitude-flux relation and disc viscosity

    NASA Astrophysics Data System (ADS)

    Zamanov, R. K.; Boeva, S.; Latev, G.; Sokoloski, J. L.; Stoyanov, K. A.; Genkov, V.; Tsvetkova, S. V.; Tomov, T.; Antov, A.; Bode, M. F.

    2016-03-01

    We analyse optical photometric data of short term variability (flickering) of accreting white dwarfs in cataclysmic variables (KR Aur, MV Lyr, V794 Aql, TT Ari, V425 Cas), recurrent novae (RS Oph and T CrB) and jet-ejecting symbiotic stars (CH Cyg and MWC 560). We find that the amplitude-flux relationship is visible over four orders of magnitude, in the range of fluxes from 1029 to 1033 erg s-1 Å-1, as a `statistically perfect correlation with correlation coefficient 0.96 and p-value ˜10-28. In the above range, the amplitude of variability for any of our 9 objects is proportional to the flux level with (almost) one and the same factor of proportionality for all nine accreting white dwarfs with ΔF = 0.36(±0.05)Fav, σrms = 0.086(±0.011)Fav, and σrms/ΔF = 0.24 ± 0.02. Overall, our results indicate that the viscosity in the accretion discs is practically the same for all nine objects in our sample, in the mass accretion rate range 2 × 10-11 - 2 × 10-7 M⊙ yr-1.

  5. Powerful radiative jets in supercritical accretion discs around non-spinning black holes

    NASA Astrophysics Data System (ADS)

    Sądowski, Aleksander; Narayan, Ramesh

    2015-11-01

    We describe a set of simulations of supercritical accretion on to a non-rotating supermassive black hole (BH). The accretion flow takes the form of a geometrically thick disc with twin low-density funnels around the rotation axis. For accretion rates {gtrsim } 10 dot{M}_Edd, there is sufficient gas in the funnel to make this region optically thick. Radiation from the disc first flows into the funnel, after which it accelerates the optically thick funnel gas along the axis. The resulting jet is baryon loaded and has a terminal density-weighted velocity ≈0.3c. Much of the radiative luminosity is converted into kinetic energy by the time the escaping gas becomes optically thin. These jets are not powered by BHrotation or magnetic driving, but purely by radiation. Their characteristic beaming angle is ˜0.2 rad. For an observer viewing down the axis, the isotropic equivalent luminosity of total energy is as much as 1048 erg s- 1 for a 107 M⊙ BH accreting at 103 Eddington. Therefore, energetically, the simulated jets are consistent with observations of the most powerful tidal disruption events, e.g. Swift J1644. The jet velocity is, however, too low to match the Lorentz factor γ > 2 inferred in J1644. There is no such conflict in the case of other tidal disruption events. Since favourably oriented observers see isotropic equivalent luminosities that are highly super-Eddington, the simulated models can explain observations of ultraluminous X-ray sources, at least in terms of luminosity and energetics, without requiring intermediate-mass BHs.

  6. Global simulations of axisymmetric radiative black hole accretion discs in general relativity with a mean-field magnetic dynamo

    NASA Astrophysics Data System (ADS)

    Sądowski, Aleksander; Narayan, Ramesh; Tchekhovskoy, Alexander; Abarca, David; Zhu, Yucong; McKinney, Jonathan C.

    2015-02-01

    We present a mean-field model that emulates the magnetic dynamo operating in magnetized accretion discs. We have implemented this model in the general relativisic radiation magnetohydrodynamic (GRRMHD) code KORAL, using results from local shearing sheet simulations of the magnetorotational instability to fix the parameters of the dynamo. With the inclusion of this dynamo, we are able to run 2D axisymmetric GRRMHD simulations of accretion discs for arbitrarily long times. The simulated discs exhibit sustained turbulence, with the poloidal and toroidal magnetic field components driven towards a state similar to that seen in 3D studies. Using this dynamo code, we present a set of long-duration global simulations of super-Eddington, optically thick discs around non-spinning and spinning black holes. Super-Eddington discs around non-rotating black holes exhibit a surprisingly large efficiency, η ≈ 0.04, independent of the accretion rate, where we measure efficiency in terms of the total energy output, both radiation and mechanical, flowing out to infinity. This value significantly exceeds the efficiency predicted by slim disc models for these accretion rates. Super-Eddington discs around spinning black holes are even more efficient, and appear to extract black hole rotational energy through a process similar to the Blandford-Znajek mechanism. All the simulated models are characterized by highly super-Eddington radiative fluxes collimated along the rotation axis. We also present a set of simulations that were designed to have Eddington or slightly sub-Eddington accretion rates (dot{M} ≲ 2dot{M}_Edd). None of these models reached a steady state. Instead, the discs collapsed as a result of runaway cooling, presumably because of a thermal instability.

  7. X-ray variability of SS 433: effects of the supercritical accretion disc

    NASA Astrophysics Data System (ADS)

    Atapin, Kirill; Fabrika, Sergei; Medvedev, Aleksei; Vinokurov, Alexander

    2015-01-01

    We study a stochastic variability of SS 433 in the 10-4-5 × 10-2 Hz frequency range based on RXTE data, and on simultaneous observations with RXTE and optical telescopes. We find that the cross-correlation functions and power spectra depend drastically on the precession phase of the supercritical accretion disc. When the wind funnel of the disc is maximally open to the observer, a flat part emerges in the power spectrum; a break is observed at the frequency 1.7 × 10-3 Hz, with a power-law index β ≈ 1.67 at higher frequencies. The soft emission forming mostly in the jets lags behind the hard and optical emission. When the observer does not see the funnel and jets (the `edge-on' disc), the power spectrum is described by a single power-law with β ≈ 1.34 and no correlations between X-ray ranges are detected. We investigated two mechanisms to explain the observed variability at the open disc phase: (1) reflection of radiation at the funnel wall (X-rays and optical) and (2) the gas cooling in the jets (X-rays only). The X-ray variability is determined by the contribution of both mechanisms; however, the contribution of the jets is much higher. We found that the funnel size is (2-2.5) × 1012 cm, and the opening angle is ϑf ˜ 50°. X-ray jets may consist of three fractions with different densities: 8 × 1013, 3 × 1013 and 5 × 1011 cm-3, with most of the jet's mass falling within the latter fraction. We suppose that revealed flat part in the power spectrum may be related to an abrupt change in the disc structure and viscous time-scale at the spherization radius, because the accretion disc becomes thick at this radius, h/r ˜ 1. The extent of the flat spectrum depends on the variation of viscosity at the spherization radius.

  8. Low-mass gas envelopes around accreting cores embedded in radiative 3D discs

    NASA Astrophysics Data System (ADS)

    Lega, Elena; Lambrechts, Michiel

    2016-10-01

    Planets with a core mass larger than few Earth masses and a gaseous envelope not exceeding about 10% of the total mass budget are common. Such planets are present in the Solar System (Uranus, Neptune) and are frequently observed around other stars.Our knowledge about the evolution of gas envelopes is mainly based on 1D models. However, such models cannot investigate the complex interaction between the forming envelope and the surrounding gas disc.In this work we perform 3D hydrodynamics simulations accounting for energy transfer and radiative cooling using the FARGOCA code (Lega et al., MNRAS 440, 2014). In addition to the usually considered heatingsources, namely viscous and compressional heating, we have modeled the energy deposited by the accretion of solids.We show that the thermal evolution of the envelope of a 5 Earth mass core is mainly dominated by compressional heating for accretion rates lower than 5 Earth masses per 105 years.Additionally, we demonstrate efficient gas circulation through the envelope. Under certain conditions, the competition between gas circulation and cooling of the envelope can efficiently delay the onset of runaway accretion. This could help in explaining the population of planets with low-mass gas envelope.

  9. Resolution requirements for smoothed particle hydrodynamics simulations of self-gravitating accretion discs

    NASA Astrophysics Data System (ADS)

    Lodato, Giuseppe; Clarke, C. J.

    2011-06-01

    Stimulated by recent results by Meru & Bate, we revisit the issue of resolution requirements for simulating self-gravitating accretion discs with smoothed particle hydrodynamics (SPH). We show that all the results by Meru & Bate are actually consistent if they are interpreted as driven by resolution effects, therefore implying that the resolution criterion for cooling gaseous discs is a function of the imposed cooling rate. We discuss two possible numerical origins of such dependence, which are both consistent with the limited number of available data. Our results tentatively indicate that convergence for current simulations is being reached for a number of SPH particles approaching 10 million (for a disc mass of the order of 10 per cent of the central object mass), which would set the critical cooling time for fragmentation at about 15Ω-1, roughly a factor of 2 larger than previously thought. More in general, we discuss the extent to which the large number of recent numerical results are reliable or not. We argue that those results that pertain to the dynamics associated with gravitational instabilities (such as the locality of angular momentum transport, and the relationship between density perturbation and induced stress) are robust, while those pertaining to the thermodynamics of the system (such as the determination of the critical cooling time for fragmentation) can be affected by poor resolution.

  10. HERO - A 3D general relativistic radiative post-processor for accretion discs around black holes

    NASA Astrophysics Data System (ADS)

    Zhu, Yucong; Narayan, Ramesh; Sadowski, Aleksander; Psaltis, Dimitrios

    2015-08-01

    HERO (Hybrid Evaluator for Radiative Objects) is a 3D general relativistic radiative transfer code which has been tailored to the problem of analysing radiation from simulations of relativistic accretion discs around black holes. HERO is designed to be used as a post-processor. Given some fixed fluid structure for the disc (i.e. density and velocity as a function of position from a hydrodynamic or magnetohydrodynamic simulation), the code obtains a self-consistent solution for the radiation field and for the gas temperatures using the condition of radiative equilibrium. The novel aspect of HERO is that it combines two techniques: (1) a short-characteristics (SC) solver that quickly converges to a self-consistent disc temperature and radiation field, with (2) a long-characteristics (LC) solver that provides a more accurate solution for the radiation near the photosphere and in the optically thin regions. By combining these two techniques, we gain both the computational speed of SC and the high accuracy of LC. We present tests of HERO on a range of 1D, 2D, and 3D problems in flat space and show that the results agree well with both analytical and benchmark solutions. We also test the ability of the code to handle relativistic problems in curved space. Finally, we discuss the important topic of ray defects, a major limitation of the SC method, and describe our strategy for minimizing the induced error.

  11. A toy model for magnetic connection in black hole accretion disc

    NASA Astrophysics Data System (ADS)

    Wang, Ding-Xiong; Ye, Yong-Chun; Li, Yang; Liu, Dong-Mei

    2007-01-01

    A toy model for magnetic connection in black hole (BH) accretion disc is discussed based on a poloidal magnetic field generated by a single electric current flowing around a Kerr BH in the equatorial plane. We discuss the effects of the coexistence of two kinds of magnetic connection (MC) arising, respectively, from (1) the closed field lines connecting the BH horizon with the disc (henceforth MCHD) and (2) the closed field lines connecting the plunging region with the disc (henceforth MCPD). The magnetic field configuration is constrained by conservation of magnetic flux and a criterion of the screw instability of the magnetic field. Two parameters λ and αm are introduced to describe our model instead of resolving the complicated magnetohydrodynamic equations. Compared with MCHD, energy and angular momentum of the plunging particles are extracted via MCPD more effectively, provided that the BH spin is not very high. It turns out that negative energy can be delivered to the BH by the plunging particles without violating the second law of BH thermodynamics, however it cannot be realized via MCPD in a stable way.

  12. Linear and non-linear evolution of the vertical shear instability in accretion discs

    NASA Astrophysics Data System (ADS)

    Nelson, Richard P.; Gressel, Oliver; Umurhan, Orkan M.

    2013-11-01

    We analyse the stability and non-linear dynamics of power-law accretion disc models. These have mid-plane densities that follow radial power laws and have either temperature or entropy distributions that are strict power-law functions of cylindrical radius, R. We employ two different hydrodynamic codes to perform high-resolution 2D axisymmetric and 3D simulations that examine the long-term evolution of the disc models as a function of the power-law indices of the temperature or entropy, the disc scaleheight, the thermal relaxation time of the fluid and the disc viscosity. We present an accompanying stability analysis of the problem, based on asymptotic methods, that we use to guide our interpretation of the simulation results. We find that axisymmetric disc models whose temperature or entropy profiles cause the equilibrium angular velocity to vary with height are unstable to the growth of perturbations whose most obvious character is modes with horizontal and vertical wavenumbers that satisfy |kR/kZ| ≫ 1. Instability occurs only when the thermodynamic response of the fluid is isothermal, or the thermal evolution time is comparable to or shorter than the local dynamical time-scale. These discs appear to exhibit the Goldreich-Schubert-Fricke or `vertical shear' linear instability. Closer inspection of the simulation results uncovers the growth of two distinct modes. The first are characterized by very short radial wavelength perturbations that grow rapidly at high latitudes in the disc, and descend down towards the mid-plane on longer time-scales. We refer to these as `finger modes' because they display kR/kZ ≫ 1. The second appear at slightly later times in the main body of the disc, including near the mid-plane. These `body modes' have somewhat longer radial wavelengths. Early on they manifest themselves as fundamental breathing modes, but quickly become corrugation modes as symmetry about the mid-plane is broken. The corrugation modes are a prominent feature

  13. Mass-loss from advective accretion disc around rotating black holes

    NASA Astrophysics Data System (ADS)

    Aktar, Ramiz; Das, Santabrata; Nandi, Anuj

    2015-11-01

    We examine the properties of the outflowing matter from an advective accretion disc around a spinning black hole. During accretion, rotating matter experiences centrifugal pressure-supported shock transition that effectively produces a virtual barrier around the black hole in the form of post-shock corona (hereafter PSC). Due to shock compression, PSC becomes hot and dense that eventually deflects a part of the inflowing matter as bipolar outflows because of the presence of extra thermal gradient force. In our approach, we study the outflow properties in terms of the inflow parameters, namely specific energy (E) and specific angular momentum (λ) considering the realistic outflow geometry around the rotating black holes. We find that spin of the black hole (ak) plays an important role in deciding the outflow rate R_{dot{m}} (ratio of mass flux of outflow to inflow); in particular, R_{dot{m}} is directly correlated with ak for the same set of inflow parameters. It is found that a large range of the inflow parameters allows global accretion-ejection solutions, and the effective area of the parameter space (E, λ) with and without outflow decreases with black hole spin (ak). We compute the maximum outflow rate (R^{max}_{dot{m}}) as a function of black hole spin (ak) and observe that R^{max}_{dot{m}} weakly depends on ak that lies in the range ˜10-18 per cent of the inflow rate for the adiabatic index (γ) with 1.5 ≥ γ ≥ 4/3. We present the observational implication of our approach while studying the steady/persistent jet activities based on the accretion states of black holes. We discuss that our formalism seems to have the potential to explain the observed jet kinetic power for several Galactic black hole sources and active galactic nuclei.

  14. Radiation-dominated boundary layer between an accretion disc and the surface of a neutron star: theory and observations

    NASA Astrophysics Data System (ADS)

    Gilfanov, M. R.; Sunyaev, R. A.

    2014-04-01

    Observations of low-mass X-ray binaries in our Galaxy and external galaxies have drawn attention to the accretion disc boundary layer where the accreting matter slows down from its Keplerian orbital velocity of about half of the speed of light to a neutron star's rotational velocity and in which it releases about half of its gravitational energy. Correspondingly, a hot spectral component appears in the emission of accreting neutron stars, which is absent in accreting black holes. We review different approaches to the problem of the radiation-dominated boundary layer. In particular, we consider the theory of a levitating spreading layer, which assumes that the accreting matter slows down while spreading over the neutron star surface.

  15. Magnetohydrodynamic Turbulence in Accretion Discs: A Test Case for Petascale Computing in Astrophysics

    NASA Astrophysics Data System (ADS)

    Joos, M.; Fromang, S.; Méheut, H.

    2015-10-01

    Angular momentum transport in accretion discs is one of the major issues of modern astrophysics and is crucial to understand as various astrophysical problematics as black hole dynamics or planet formation. Angular momentum transport relies on magnetohydrodynamic (MHD) turbulence, responsible for the non-linear evolution of the magneto-rotational instability (MRI). 3D simulations are essential to determine the physical properties of the flow resulting from that instability. In particular, the angular momentum transport rate induced by the MRI is difficult to estimate, depending on dissipation rates which are linked to viscous and resistive scales. These dissipation scales can be much smaller than the typical scale of the system and to simulate flows with such properties is very challenging. We recently realized a simulation on a BlueGene/Q with the smallest viscous dissipation coefficient ever reached. We discuss the challenges encountered in this context and the developments realized regarding efficient parallel Input/Output, hybridation and porting on GPGPU.

  16. The signature of the magnetorotational instability in the Reynolds and Maxwell stress tensors in accretion discs

    NASA Astrophysics Data System (ADS)

    Pessah, Martin E.; Chan, Chi-Kwan; Psaltis, Dimitrios

    2006-10-01

    The magnetorotational instability is thought to be responsible for the generation of magnetohydrodynamic turbulence that leads to enhanced outward angular momentum transport in accretion discs. Here, we present the first formal analytical proof showing that, during the exponential growth of the instability, the mean (averaged over the disc scaleheight) Reynolds stress is always positive, the mean Maxwell stress is always negative, and hence the mean total stress is positive and leads to a net outward flux of angular momentum. More importantly, we show that the ratio of the Maxwell to the Reynolds stresses during the late times of the exponential growth of the instability is determined only by the local shear and does not depend on the initial spectrum of perturbations or the strength of the seed magnetic field. Even though we derived this property of the stress tensors for the exponential growth of the instability in incompressible flows, numerical simulations of shearing boxes show that this characteristic is qualitatively preserved under more general conditions, even during the saturated turbulent state generated by the instability.

  17. Long-term quasi-periodicity of 4U 1636-536 resulting from accretion disc instability

    NASA Astrophysics Data System (ADS)

    Wisniewicz, Mateusz; Zdziarski, Andrzej; Janiuk, Agnieszka; Rosinska, Dorota; Slowikowska, Agnieszka

    2016-07-01

    We present the results of a study of the low-mass X-ray binary 4U 1636-536. We have performed temporal analysis of all available RXTE/ASM, RXTE/PCA, Swift/BAT and MAXI data. We have confirmed the previously discovered quasi-periodicity of ˜45 d present during ˜2004, however we found it continued to 2006. At other epochs, the quasi-periodicity is only transient, and the quasi-period, if present, drifts. We have then applied a time-dependent accretion disc model to the interval with the significant X-ray quasi-periodicity. For our best model, the period and the amplitude of the theoretical light curve agree well with that observed. The modelled quasi-periodicity is due to the hydrogen thermal-ionization instability occurring in outer regions of the accretion disc. The model parameters are the average mass accretion rate (estimated from the light curves), and the accretion disc viscosity parameters, α_{cold} and α_{hot}, for the hot and cold phases, respectively. Our best model gives relatively low values of α_{cold} and α_{hot}.

  18. The mass donor star and the accretion disc of the dwarf nova V2051 Ophiuchi in the infrared

    NASA Astrophysics Data System (ADS)

    Wojcikiewicz, Eduardo; Baptista, Raymundo; Ribeiro, Tiago

    2016-07-01

    We report the analysis of infrared JHK_s high speed photometry of the dwarf nova V2051 Oph in quiescence. We model the ellipsoidal variations in the light curve to measure the fluxes of the mass donor star. Its colors are consistent with an M8 ± 1 spectral type with an equivalent blackbody temperature of T_{bb}= (2700± 300) K, in agreement with spectroscopic measurements and with theoretical expectation for donor stars at the same orbital period. We use the mass donor star fluxes and the Barnes & Evans relation to find a photometric parallax distance of (102 ± 16) pc to the binary. At this distance the outbursts of V2051 Oph occur at disc temperatures everywhere lower than the minimum/critical temperature predicted by the disc instability model, underscoring previous suggestions that they are powered by mass transfer bursts. We subtract the contribution of the mass donor star and apply eclipse mapping techniques to the remaining light curve in order to investigate the structure and emission of its accretion disc. The infrared accretion disc is bright and 'blue' in the inner regions and becomes progressively fainter and redder with increasing radii, indicating that the disc temperature decreases with radius. Bulges in the eclipse shape, more prominent in the H and K_s bands, lead to asymmetric arcs in the eclipse maps reminiscent of the spiral arms found in disc maps of outbursting dwarf novae. The arcs show an azimuthal extent of ˜90^o, extend from the intermediate to the outer disc regions (0.3-0.4 R_{L1}, where R_{L1} is the distance from disc center to the inner lagrangian point), and account for ≃ 30 per cent of the total flux in the H and K_s bands.

  19. Comparison of ejection events in the jet and accretion disc outflows in 3C 111

    NASA Astrophysics Data System (ADS)

    Tombesi, F.; Sambruna, R. M.; Marscher, A. P.; Jorstad, S. G.; Reynolds, C. S.; Markowitz, A.

    2012-07-01

    We present a comparison of the parameters of accretion disc outflows and the jet of the broad-line radio galaxy 3C 111 on subparsec (sub-pc) scales. We make use of published X-ray observations of ultra-fast outflows (UFOs) and new 43-GHz Very Long Baseline Array images to track the jet knot ejection. We find that the superluminal jet coexists with the mildly relativistic outflows on sub-pc scales, possibly indicating a transverse stratification of a global flow. The two are roughly in pressure equilibrium, with the UFOs potentially providing additional support for the initial jet collimation. The UFOs are much more massive than the jet, but their kinetic power is probably about an order of magnitude lower, at least for the observations considered here. However, their momentum flux is equivalent and both of them are powerful enough to exert a concurrent feedback impact on the surrounding environment. A link between these components is naturally predicted in the context of magnetohydrodynamic models for jet/outflow formation. However, given the high radiation throughput of active galactic nuclei, radiation pressure should also be taken into account. From the comparison with the long-term 2-10 keV Rossi X-ray Timing Explorer light curve, we find that the UFOs are preferentially detected during periods of increasing flux. We also find the possibility to place the UFOs within the known X-ray dips-jet ejection cycles, which has been shown to be a strong proof of the disc-jet connection, in analogue with stellar mass black holes. However, given the limited number of observations presently available, these relations are only tentative and additional spectral monitoring is needed to test them conclusively.

  20. Comparison of Ejection Events in the Jet and Accretion Disc Outflows in 3C 111

    NASA Technical Reports Server (NTRS)

    Tombesi, F.; Sambruna, R. M.; Marscher, A. P.; Jorstad, S. G.; Reynolds, C. S.; Markowtiz, A.

    2012-01-01

    We present a comparison of the parameters of accretion disc outflows and the jet of the broad-line radio galaxy 3C 111 on sub-pc scales. We make use of published X-ray observations of ultra-fast outflows (UFOs) and new 43 GHz VLBA images to track the jet knots ejection. We find that the superluminal jet coexists with the mildly relativistic outflows on sub-pc scales, possibly indicating a transverse stratification of a global flow. The two are roughly in pressure equilibrium, with the UFOs potentially providing additional support for the initial jet collimation. The UFOs are much more massive than the jet, but their kinetic power is probably about an order of magnitude lower, at least for the observations considered here. However, their momentum flux is equivalent and both of them are powerful enough to exert a concurrent feedback impact on the surrounding environment. A link between these components is naturally predicted in the context of MHD models for jet/outflow formation. However, given the high radiation throughput of AGNs, radiation pressure should also be taken into account. From the comparison with the long-term 2-10 keV RXTE light curve we find that the UFOs are preferentially detected during periods of increasing flux. We also find the possibility to place the UFOs within the known X-ray dips-jet ejection cycles, which has been shown to be a strong proof of the disc-jet connection, in analogue with stellar-mass black holes. However, given the limited number of observations presently available, these relations are only tentative and additional spectral monitoring is needed to test them conclusively.

  1. SOAR observations of the high-viscosity accretion disc of the dwarf nova V4140 Sagitarii in quiescence and in outburst

    NASA Astrophysics Data System (ADS)

    Baptista, Raymundo; Borges, Bernardo W.; Oliveira, Alexandre S.

    2016-09-01

    We report the analysis of 22 B-band light curves of the dwarf nova V4140 Sgr obtained with SOI/SOAR during two nights along the decline of a superoutburst in 2006 Sep 12-24 and in quiescence over 50 days following the superoutburst. Three-dimensional eclipse mapping of the outburst light curves indicates that the accretion disc is elliptical (eccentricity e = 0.13) and that superhump maximum occurs when the mass donor star is aligned with the bulge of the elliptical disc. The accretion disc is geometrically thin both in outburst and in quiescence; it fills the primary Roche lobe in outburst and shrinks to about half this size in quiescence. The stability of the eclipse shape, width and depth along quiescence and the derived disc surface brightness distribution indicate that the quiescent accretion disc is in a high-viscosity, steady-state. Flickering mapping of the quiescent data reveal that the low-frequency flickering arises from an azimuthally-extended stream-disc impact region at disc rim and from the innermost disc region, whereas the high-frequency flickering originates in the accretion disc. Assuming the disc-related flickering to be caused by fluctuations in the energy dissipation rate induced by magneto-hydrodynamic turbulence (Geertsema & Achterberg 1992), we find that the quiescent disc viscosity parameter is large α ≃ 0.2 - 0.4 at all radii. The high-viscosity quiescent disc and the inferred low disc temperatures in superoutburst are inconsistent with expectations of the disc-instability model, and lead to the conclusion that the outbursts of V4140 Sgr are powered by mass transfer bursts from its donor star.

  2. Collective molecular dissipation on Navier-Stokes macroscopic scales: Accretion disc viscous modeling in SPH

    NASA Astrophysics Data System (ADS)

    Lanzafame, Giuseppe

    2015-02-01

    In the nonlinear Navier-Stokes viscous flow dynamics, physical damping is mathematically accomplished by a braking term in the momentum equation, corresponding to a heating term in the energy equation, both responsible of the conversion of mechanical energy into heat. In such two terms, it is essential the role of the viscous stress tensor, relative to contiguous macroscopic moving flow components, depending on the macroscopic viscosity coefficient ν. A working formulation for ν can always be found analytically, tuning some arbitrary parameters in the current known formulations, according to the geometry, morphology and physics of the flow. Instead, in this paper, we write an alternative hybrid formulation for ν, where molecular parameters are also included. Our expression for ν has a more physical interpretation of the internal damping in dilute gases because the macroscopic viscosity is related to the small scale molecular dissipation, not strictly dependent on the flow morphology, as well as it is free of any arbitrary parameter. Results for some basic 2D tests are shown in the smoothed particle hydrodynamics (SPH) framework. An application to the 3D accretion disc modeling for low mass cataclysmic variables is also discussed. Consequences of the macroscopic viscosity coefficient reformulation in a more strictly physical terms on the thermal conductivity coefficient for dilute gases are also discussed.

  3. Active galactic nuclei at z ˜ 1.5 - III. Accretion discs and black hole spin

    NASA Astrophysics Data System (ADS)

    Capellupo, D. M.; Netzer, H.; Lira, P.; Trakhtenbrot, B.; Mejía-Restrepo, J.

    2016-07-01

    This is the third paper in a series describing the spectroscopic properties of a sample of 39 AGN at z ˜ 1.5, selected to cover a large range in black hole mass (MBH) and Eddington ratio (L/LEdd). In this paper, we continue the analysis of the VLT/X-shooter observations of our sample with the addition of nine new sources. We use an improved Bayesian procedure, which takes into account intrinsic reddening, and improved MBH estimates, to fit thin accretion disc (AD) models to the observed spectra and constrain the spin parameter (a*) of the central black holes. We can fit 37 out of 39 AGN with the thin AD model, and for those with satisfactory fits, we obtain constraints on the spin parameter of the BHs, with the constraints becoming generally less well defined with decreasing BH mass. Our spin parameter estimates range from ˜-0.6 to maximum spin for our sample, and our results are consistent with the `spin-up' scenario of BH spin evolution. We also discuss how the results of our analysis vary with the inclusion of non-simultaneous GALEX photometry in our thin AD fitting. Simultaneous spectra covering the rest-frame optical through far-UV are necessary to definitively test the thin AD theory and obtain the best constraints on the spin parameter.

  4. Line and continuum radiation from the outer region of accretion discs in active galactic nuclei. I - Preliminary considerations

    NASA Astrophysics Data System (ADS)

    Collin-Souffrin, S.

    1987-06-01

    The structure and emission of the optically thin region of steady accretion discs in Active Galactic Nuclei (AGN) is investigated. It is shown that this region is located far from the center (R/RG very large 102). If its only energy source is provided by accretion, the temperature is very low (1000 - 2000K) and therefore it cannot be identified with the broad line emitting region (BLR). The overall emission of the optically thin region is negligible, except in the infrared at a few microns, where it gives some contribution of the "5 μ-bump". However it is found that, if the disc is heated by the down scattered part of the non-thermal continuum observed in AGN, the physical parameters of the optically thin region satisfy the requirements of photoionization models for the line emission. Hard X-ray heating of the external regions of accretion discs is the source of the "missing energy" in the budget of the BLR (Collin-Souffrin, 1986) and moreover gives rise to an intense infrared thermal continuum able to account for the 5 μ bump. Finally this model could solve the "Fell problem".

  5. An accretion disc-irradiation hybrid model for the optical/UV variability in radio-quiet quasars

    NASA Astrophysics Data System (ADS)

    Liu, Hui; Li, Shuang-Liang; Gu, Minfeng; Guo, Hengxiao

    2016-10-01

    The optical/ultraviolet (UV) variability of quasars has been discovered to be correlated with other quasar properties, such as luminosity, black hole mass and rest-frame wavelength. However, the origin of variability has been a puzzle so far. In this work, we upgrade the accretion disc model, which assumed the variability is caused by the change of global mass accretion rate, by constraining the disc size to match the viscous time-scale of accretion disc to the variability time-scale observed and by including the irradiation/X-ray reprocessing to make the emitted spectrum become steeper. We find this hybrid model can reproduce the observed bluer-when-brighter trend quite well, which is used to validate the theoretical model by several works recently. The traditional correlation between the variability amplitude and rest-frame wavelength can also be well fitted by our model. In addition, a weak positive correlation between variability amplitude and black hole mass is present, qualitatively consistent with recent observations.

  6. Probing the Inner Relativistic Accretion Disc in 4u 1705-44 with RXTE and Xmm-Newton

    NASA Astrophysics Data System (ADS)

    di Salvo, Tiziana

    We propose to observe the X-ray burster Low Mass X-ray Binary 4U 1705- 44 with RXTE simultaneously with XMM-Newton for 200 ks. This observation will give us the possibility to confirm the disc reflection origin of the relativistic iron line observed by XMM in this source extending the spectral energy response to 200 keV and giving us the possibility to fit the broad band spectrum with self-consistent reflection models. The RXTE observation will also give us the possibility to detect kHz QPOs and to test the paradigm that their frequencies, as envisaged by most of the models, correspond to the Keplerian frequency at the inner accretion disc. This can be done by comparing the inner disc radius derived by the kHz QPO frequencies with that derived by fitting the relativistic iron line profile.

  7. Super- and sub-Eddington accreting massive black holes: a comparison of slim and thin accretion discs through study of the spectral energy distribution

    NASA Astrophysics Data System (ADS)

    Castelló-Mor, N.; Netzer, H.; Kaspi, S.

    2016-05-01

    We employ optical and ultraviolet (UV) observations to present spectral energy distributions (SEDs) for two reverberation-mapped samples of super-Eddington and sub-Eddington active galactic nuclei (AGN) with similar luminosity distributions. The samples are fitted with accretion disc (AD) models in order to look for SED differences that depend on the Eddington ratio. The fitting takes into account measured black hole (BH) mass and accretion rates, BH spin and intrinsic reddening of the sources. All objects in both groups can be fitted by thin AD models over the range 0.2-1 μm with reddening as a free parameter. The intrinsic reddening required to fit the data are relatively small, E(B - V) ≤ 0.2 mag, except for one source. Super-Eddington AGN seems to require more reddening. The distribution of E(B - V) is similar to what is observed in larger AGN samples. The best-fitting disc models recover very well the BH mass and accretion for the two groups. However, the SEDs are very different, with super-Eddington sources requiring much more luminous far-UV continuum. The exact amount depends on the possible saturation of the UV radiation in slim discs. In particular, we derive for the super-Eddington sources a typical bolometric correction at 5100 Å of 60-150 compared with a median of ˜20 for the sub-Eddington AGN. The measured torus luminosity relative to λLλ(5100 Å) are similar in both groups. The αOX distribution is similar too. However, we find extremely small torus covering factors for super-Eddington sources, an order of magnitude smaller than those of sub-Eddington AGN. The small differences between the groups regarding the spectral range 0.2-22 μm, and the significant differences related to the part of the SED that we cannot observe may be consistent with some slim disc models. An alternative explanation is that present day slim-disc models overestimate the far-UV luminosity of such objects by a large amount.

  8. Accretion disc dynamo activity in local simulations spanning weak-to-strong net vertical magnetic flux regimes

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    Strongly magnetized accretion discs around black holes have attractive features that may explain enigmatic aspects of X-ray binary behaviour. The structure and evolution of these discs are governed by a dynamo-like mechanism, which channels part of the accretion power liberated by the magnetorotational instability (MRI) into an ordered toroidal magnetic field. To study dynamo activity, we performed three-dimensional, stratified, isothermal, ideal magnetohydrodynamic shearing box simulations. The strength of the self-sustained toroidal magnetic field depends on the net vertical magnetic flux, which we vary across almost the entire range over which the MRI is linearly unstable. We quantify disc structure and dynamo properties as a function of the initial ratio of mid-plane gas pressure to vertical magnetic field pressure, β _0^mid = p_gas / p_B. For 10^5 ≥ β _0^mid ≥ 10 the effective α-viscosity parameter scales as a power law. Dynamo activity persists up to and including β _0^mid = 10^2, at which point the entire vertical column of the disc is magnetic pressure dominated. Still stronger fields result in a highly inhomogeneous disc structure, with large density fluctuations. We show that the turbulent steady state βmid in our simulations is well matched by the analytic model of Begelman et al. describing the creation and buoyant escape of toroidal field, while the vertical structure of the disc can be broadly reproduced using this model. Finally, we discuss the implications of our results for observed properties of X-ray binaries.

  9. Transport of magnetic flux and the vertical structure of accretion discs - II. Vertical profile of the diffusion coefficients

    NASA Astrophysics Data System (ADS)

    Guilet, Jérôme; Ogilvie, Gordon I.

    2013-04-01

    We investigate the radial transport of magnetic flux in a thin accretion disc, the turbulence being modelled by effective diffusion coefficients (viscosity and resistivity). Both turbulent diffusion and advection by the accretion flow contribute to flux transport, and they are likely to act in opposition. We study the consequences of the vertical variation of the diffusion coefficients, due to a varying strength of the turbulence. For this purpose, we consider three different vertical profiles of these coefficients. The first one is aimed at mimicking the turbulent stress profile observed in numerical simulations of magnetohydrodynamic turbulence in stratified discs. This enables us to confirm the robustness of the main result of Paper I obtained for uniform diffusion coefficients that, for weak magnetic fields, the contribution of the accretion flow to the transport velocity of magnetic flux is much larger than the transport velocity of mass. We then consider the presence of a dead zone around the equatorial plane where the physical resistivity is high while the turbulent viscosity is low. We find that it amplifies the previous effect: weak magnetic fields can be advected orders of magnitude faster than mass, for dead zones with a large vertical extension. The ratio of advection to diffusion, determining the maximum inclination of the field at the surface of the disc, is however not much affected. Finally, we study the effect of a non-turbulent layer at the surface of the disc, which has been suggested as a way to reduce the diffusion of the magnetic flux. We find that the reduction of the diffusion requires the conducting layer to extend below the height at which the magnetic pressure equals the thermal pressure. As a consequence, if the absence of turbulence is caused by the large-scale magnetic field, the highly conducting layer is inefficient at reducing the diffusion.

  10. Discovery of 15 Myr Old pre-Main Sequence Stars with Active Accretion and Sizeable Discs in NGC 6611

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, N.; Guarcello, M. G.; Bonito, R.

    2012-01-01

    Attention is given to a population of 110 stars with prominent near-infrared (NIR) excess in the NGC 6611 cluster of the Eagle Nebula that have optical colours typical of pre-main sequence (PMS) stars older than 10 Myr. In principle, their V-I colours would be consistent with those of young PMS objects (< 1 Myr), whose radiation is heavily obscured by a circumstellar disc seen at high inclination and in small part scattered towards the observer by the back side of the disc. However, using theoretical models it is shown here that objects of this type can only account for a few percent of this population. In fact, the spatial distribution of these objects, their X-ray luminosities, their optical brightness and their positions in the colour-magnitude diagram unambiguously indicate that most of these stars are intrinsically older than 10 Myr. Ages range from 8 to 30 Myr with a median value of 15 Myr. This is the largest homogeneous sample to date of Galactic PMS stars considerably older than 10 Myr that are still actively accreting from a circumstellar disc and it allows us to set a lower limit of 5% to the disc frequency at 15 Myr in NGC 6611. These values imply a characteristic exponential lifetime of 5 Myr for disc dissipation.

  11. Convergence of smoothed particle hydrodynamics simulations of self-gravitating accretion discs: sensitivity to the implementation of radiative cooling

    NASA Astrophysics Data System (ADS)

    Rice, W. K. M.; Forgan, D. H.; Armitage, P. J.

    2012-02-01

    Recent simulations of self-gravitating accretion discs, carried out using a three-dimensional smoothed particle hydrodynamics (SPH) code by Meru & Bate, have been interpreted as implying that three-dimensional global discs fragment much more easily than would be expected from a two-dimensional local model. Subsequently, global and local two-dimensional models have been shown to display similar fragmentation properties, leaving it unclear whether the three-dimensional results reflect a physical effect or a numerical problem associated with the treatment of cooling or artificial viscosity in SPH. Here, we study how fragmentation of self-gravitating disc flows in SPH depends upon the implementation of cooling. We run disc simulations that compare a simple cooling scheme, in which each particle loses energy based upon its internal energy per unit mass, with a method in which the cooling is derived from a smoothed internal energy density field. For the simple per particle cooling scheme, we find a significant increase in the minimum cooling time-scale for fragmentation with increasing resolution, matching previous results. Switching to smoothed cooling, however, results in lower critical cooling time-scales, and tentative evidence for convergence at the highest spatial resolution tested. We conclude that precision studies of fragmentation using SPH require careful consideration of how cooling (and, probably, artificial viscosity) is implemented, and that the apparent non-convergence of the fragmentation boundary seen in prior simulations is likely a numerical effect. In real discs, where cooling is physically smoothed by radiative transfer effects, the fragmentation boundary is probably displaced from the two-dimensional value by a factor that is only of the order of unity.

  12. HST Spatially Resolved Spectra of the Accretion Disc and Gas Stream of the Nova-Like Variable UX Ursae Majoris

    NASA Technical Reports Server (NTRS)

    Baptista, Raymundo; Horne, Keith; Wade, Richard A.; Hubeny, Ivan; Long, Knox S.; Rutten, Rene G. M.

    1998-01-01

    Time-resolved eclipse spectroscopy of the nova-like variable UX UMa obtained with the Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) on 1994 August and November is analysed with eclipse mapping techniques to produce spatially resolved spectra of its accretion disk and gas stream as a function of distance from the disk centre. The inner accretion disk is characterized by a blue continuum filled with absorption bands and lines, which cross over to emission with increasing disk radius, similar to that reported at optical wavelengths. The comparison of spatially resolved spectra at different azimuths reveals a significant asymmetry in the disk emission at ultraviolet (UV) wavelengths, with the disk side closest to the secondary star showing pronounced absorption by an 'iron curtain' and a Balmer jump in absorption. These results suggest the existence of an absorbing ring of cold gas whose density and/or vertical scale increase with disk radius. The spectrum of the infalling gas stream is noticeably different from the disc spectrum at the same radius suggesting that gas overflows through the impact point at the disk rim and continues along the stream trajectory, producing distinct emission down to 0.1 R(sub LI). The spectrum of the uneclipsed light shows prominent emission lines of Lyalpha, N v lambda1241, SiIV Lambda 1400, C IV Lambda 1550, HeII Lambda 1640, and MgII Lambda 2800, and a UV continuum rising towards longer wavelengths. The Balmer jump appears clearly in emission indicating that the uneclipsed light has an important contribution from optically thin gas. The lines and optically thin continuum emission are most probably emitted in a vertically extended disk chromosphere + wind. The radial temperature profiles of the continuum maps are well described by a steady-state disc model in the inner and intermediate disk regions (R greater than or equal to 0.3R(sub LI) ). There is evidence of an increase in the mass accretion rate from August to November

  13. The dead zone size limits in a proto-stellar accretion disc model heated by the damping of Alfvén waves

    NASA Astrophysics Data System (ADS)

    Jatenco-Pereira, V.

    2015-05-01

    Heating of proto-stellar accretion discs has been studied by several authors. Jatenco-Pereira (Mon. Not. R. Astron. Soc. 431:3150, 2013) proposed a disc model with two heating mechanisms: the "anomalous" viscosity considered in terms of the α-prescription and the damping of Alfvén waves. As the discs are composed of dust, it was considered that when charged dust particles acquire the same (cyclotron) frequency as the waves, a resonance occurs that leads to the damping of the waves. Here we show that the increase in the temperature of the disc midplane implies in the reduction of the size of the quiescent region in proto-stellar discs and compare it with the actual position of the solar system planets.

  14. X-ray coherent pulsations during a sub-luminous accretion disc state of the transitional millisecond pulsar XSS J12270-4859

    NASA Astrophysics Data System (ADS)

    Papitto, A.; de Martino, D.; Belloni, T. M.; Burgay, M.; Pellizzoni, A.; Possenti, A.; Torres, D. F.

    2015-04-01

    We present the first detection of X-ray coherent pulsations from the transitional millisecond pulsar XSS J12270-4859, while it was in a sub-luminous accretion disc state characterized by a 0.5-10 keV luminosity of 5 × 1033 erg s-1 (assuming a distance of 1.4 kpc). Pulsations were observed by XMM-Newton at an rms amplitude of (7.7 ± 0.5) per cent with a second harmonic stronger than the fundamental frequency, and were detected when the source is neither flaring nor dipping. The most likely interpretation of this detection is that matter from the accretion disc was channelled by the neutron star magnetosphere and accreted on to its polar caps. According to standard disc accretion theory, for pulsations to be observed the mass inflow rate in the disc was likely larger than the amount of plasma actually reaching the neutron star surface; an outflow launched by the fast rotating magnetosphere then probably took place, in agreement with the observed broad-band spectral energy distribution. We also report about the non-detection of X-ray pulsations during a recent observation performed while the source behaved as a rotationally-powered radio pulsar.

  15. The effects of high density on the X-ray spectrum reflected from accretion discs around black holes

    NASA Astrophysics Data System (ADS)

    García, Javier A.; Fabian, Andrew C.; Kallman, Timothy R.; Dauser, Thomas; Parker, Michael L.; McClintock, Jeffrey E.; Steiner, James F.; Wilms, Jörn

    2016-10-01

    Current models of the spectrum of X-rays reflected from accretion discs around black holes and other compact objects are commonly calculated assuming that the density of the disc atmosphere is constant within several Thomson depths from the irradiated surface. An important simplifying assumption of these models is that the ionization structure of the gas is completely specified by a single, fixed value of the ionization parameter ξ, which is the ratio of the incident flux to the gas density. The density is typically fixed at ne = 1015 cm-3. Motivated by observations, we consider higher densities in the calculation of the reflected spectrum. We show by computing model spectra for ne ≳ 1017 cm-3 that high-density effects significantly modify reflection spectra. The main effect is to boost the thermal continuum at energies ≲ 2 keV. We discuss the implications of these results for interpreting observations of both active galactic nuclei and black hole binaries. We also discuss the limitations of our models imposed by the quality of the atomic data currently available.

  16. Time-dependent models of accretion discs with nuclear burning following the tidal disruption of a white dwarf by a neutron star

    NASA Astrophysics Data System (ADS)

    Margalit, Ben; Metzger, Brian D.

    2016-09-01

    We construct time-dependent one-dimensional (vertically averaged) models of accretion discs produced by the tidal disruption of a white dwarf (WD) by a binary neutron star (NS) companion. Nuclear reactions in the disc mid-plane burn the WD matter to increasingly heavier elements at sequentially smaller radii, releasing substantial energy which can impact the disc dynamics. A model for disc outflows is employed, by which cooling from the outflow balances other sources of heating (viscous, nuclear) in regulating the Bernoulli parameter of the mid-plane to a fixed value ≲0. We perform a comprehensive parameter study of the compositional yields and velocity distributions of the disc outflows for WDs of different initial compositions. For C/O WDs, the radial composition profile of the disc evolves self-similarly in a quasi-steady-state manner, and is remarkably robust to model parameters. The nucleosynthesis in helium WD discs does not exhibit this behaviour, which instead depends sensitively on factors controlling the disc mid-plane density (e.g. the strength of the viscosity, α). By the end of the simulation, a substantial fraction of the WD mass is unbound in outflows at characteristic velocities of ˜109 cm s-1. The outflows from WD-NS merger discs contain 10-4-3 × 10-3 M⊙ of radioactive 56Ni, resulting in fast (˜ week long) dim (˜1040 erg s-1) optical transients; shock heating of the ejecta by late-time outflows may increase the peak luminosity to ˜1043 erg s-1. The accreted mass on to the NS is probably not sufficient to induce gravitational collapse, but may be capable of spinning up the NS to periods of ˜10 ms, illustrating the feasibility of this channel in forming isolated millisecond pulsars.

  17. Testing black hole neutrino-dominated accretion discs for long-duration gamma-ray bursts

    NASA Astrophysics Data System (ADS)

    Song, Cui-Ying; Liu, Tong; Gu, Wei-Min; Tian, Jian-Xiang

    2016-05-01

    Long-duration gamma-ray bursts (LGRBs) are generally considered to originate from the massive collapsars. It is believed that the central engine of gamma-ray bursts (GRBs) is a neutrino-dominated accretion flow (NDAF) around a rotating stellar-mass black hole (BH). The neutrino annihilation above the NDAF is a feasible mechanism to power GRB. In this work, we analyse the distributions of the isotropic gamma-ray-radiated energy and jet kinetic energy of 48 LGRBs. According to the NDAF and fireball models, we estimate the mean accreted masses of LGRBs in our sample to investigate whether the NDAFs can power LGRBs with the reasonable BH parameters and conversion efficiency of neutrino annihilation. The results indicate that most of the values of the accreted masses are less than 5 M⊙ for the extreme Kerr BHs and high conversion efficiency. It suggests that the NDAFs may be suitable for most of LGRBs except for some extremely high energy sources.

  18. Accretion disc-corona and jet emission from the radio-loud narrow-line Seyfert 1 galaxy RX J1633.3+4719

    NASA Astrophysics Data System (ADS)

    Mallick, Labani; Dewangan, G. C.; Gandhi, P.; Misra, R.; Kembhavi, A. K.

    2016-08-01

    We perform X-ray/ultraviolet (UV) spectral and X-ray variability studies of the radio-loud narrow-line Seyfert 1 (NLS1) galaxy RX J1633.3+4719 using XMM-Newton and Suzaku observations from 2011 and 2012. The 0.3-10 keV spectra consist of an ultrasoft component described by an accretion disc blackbody (kT_in = 39.6^{+11.2}_{-5.5} eV) and a power law due to the thermal Comptonization (Γ = 1.96^{+0.24}_{-0.31}) of the disc emission. The disc temperature inferred from the soft excess is at least a factor of 2 lower than that found for the canonical soft excess emission from radio-quiet NLS1s. The UV spectrum is described by a power law with photon index 3.05^{+0.56}_{-0.33}. The observed UV emission is too strong to arise from the accretion disc or the host galaxy, but can be attributed to a jet. The X-ray emission from RX J1633.3+4719 is variable with fractional variability amplitude Fvar = 13.5 ± 1.0 per cent. In contrast to radio-quiet active galactic nuclei (AGN), X-ray emission from the source becomes harder with increasing flux. The fractional rms variability increases with energy and the rms spectrum is well described by a constant disc component and a variable power-law continuum with the normalization and photon index being anticorrelated. Such spectral variability cannot be caused by variations in the absorption and must be intrinsic to the hot corona. Our finding of possible evidence for emission from the inner accretion disc, jet and hot corona from RX J1633.3+4719 in the optical to X-ray bands makes this object an ideal target to probe the disc-jet connection in AGN.

  19. Accretion disc geometry evolution of GRS 1915+105 during its plataeu states

    NASA Astrophysics Data System (ADS)

    Sarathi Pal, Partha; Gopal Dutta, Broja; Chakrabarti, Sandip Kumar

    2016-07-01

    The evolution of Time-lags are correlated with the accretion geometry during Plateau states of GRS 1915+105. We find that the lag spectrum for the χ_3 class is different from that of χ_1, χ_2 and χ_4 classes. Hard lags occur only when Comptonizing efficiency (CE) is about 0.9% for different plateau states and its evolution follows the sequence of class transitions suggested on the basis of CE parameter. We conclude that the variation of time lags could be due to change of size of the CENBOL which is often triggered by Compton cooling process.

  20. A relativistically smeared spectrum in the neutron star X-ray binary 4U 1705-44: looking at the inner accretion disc with X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    di Salvo, T.; D'Aí, A.; Iaria, R.; Burderi, L.; Dovčiak, M.; Karas, V.; Matt, G.; Papitto, A.; Piraino, S.; Riggio, A.; Robba, N. R.; Santangelo, A.

    2009-10-01

    Iron emission lines at 6.4-6.97 keV, identified with fluorescent Kα transitions, are among the strongest discrete features in the X-ray band. These are therefore one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent XMM-Newton observation of the X-ray burster 4U 1705-44, where we clearly detect a relativistically smeared iron line at about 6.7 keV, testifying with high statistical significance that the line profile is distorted by high-velocity motion in the accretion disc. As expected from disc reflection models, we also find a significant absorption edge at about 8.3 keV; this feature appears to be smeared, and is compatible with being produced in the same region where the iron line is produced. From the line profile, we derive the physical parameters of the inner accretion disc with large precision. The line is identified with the Kα transition of highly ionized iron, FeXXV, the inner disc radius is Rin = 14 +/- 2 Rg (where Rg is the Gravitational radius, GM/c2), the emissivity dependence from the disc radius is r-2.27+/-0.08, the inclination angle with respect to the line of sight is i = 39° +/- 1°. Finally, the XMM-Newton spectrum shows evidences of other low-energy emission lines, which again appear broad and their profiles are compatible with being produced in the same region where the iron line is produced.

  1. Revisiting linear dynamics of non-axisymmetric perturbations in weakly magnetized accretion discs

    NASA Astrophysics Data System (ADS)

    Mamatsashvili, G. R.; Chagelishvili, G. D.; Bodo, G.; Rossi, P.

    2013-11-01

    We investigate the linear dynamics of non-axisymmetric perturbations in incompressible, vertically stratified Keplerian discs threaded by a weak non-zero net vertical magnetic field in the local shearing box approximation. Perturbations are decomposed into shearing waves or spatial harmonics whose temporal evolution is then followed via numerical integration of the linearized ideal magnetohydrodynamic equations of the shearing box. There are two basic modes in the system - inertia-gravity waves and magnetic mode, which displays the magnetorotational instability (MRI). Distinct from previous related studies, we introduce `eigen-variables' characterizing each (counter-propagating) component of the inertia-gravity and magnetic modes, which are governed by a set of four first-order coupled ordinary differential equations. This allows us to identify a new process of linear coupling of the two above non-axisymmetric modes due to the disc's differential rotation. We also carry out a comparative analysis of the dynamics of non-axisymmetric and axisymmetric magnetic mode perturbations. It is demonstrated that the growth of `optimal' and close-to-optimal non-axisymmetric harmonics of this mode, having transient nature, can prevail over the exponential growth of axisymmetric ones (i.e. over the axisymmetric MRI) during dynamical time. A possible implication of this result for axisymmetric channel solutions emerging in numerical simulations is discussed. In particular, the formation of the (axisymmetric) channel may be affected/impeded by non-axisymmetric modes already at the early linear stage leading to its untimely disruption - the outcome strongly depends on the amplitude and spectrum of initial perturbation. Thus, this competition may result in an uncertainty in the magnetic mode's non-linear dynamics. Even so, we consider that incompressible perturbations, in the final part, speculate on the dynamics in the compressible case. It is shown that a maximum growth of non

  2. Colours of black holes: infrared flares from the hot accretion disc in XTE J1550-564

    NASA Astrophysics Data System (ADS)

    Poutanen, Juri; Veledina, Alexandra; Revnivtsev, Mikhail G.

    2014-12-01

    Outbursts of the black hole (BH) X-ray binaries are dramatic events occurring in our Galaxy approximately once a year. They are detected by the X-ray telescopes and often monitored at longer wavelengths. We analyse the X-ray and optical/infrared (OIR) light curves of the BH binary XTE J1550-564 during the 2000 outburst. By using the observed extreme colours as well as the characteristic decay time-scales of the OIR and X-ray light curves, we put strong constraints on the extinction towards the source. We accurately separate the contributions to the OIR flux of the irradiated accretion disc and a non-thermal component. We show that the OIR non-thermal component appears during the X-ray state transitions both during the rising and the decaying part of the outburst at nearly the same X-ray hardness but at luminosities differing by a factor of 3. The line marking the quenching/recovery of the non-thermal component at the X-ray hardness-flux diagram seems to coincide with the `jet line' that marks the presence of the compact radio jet. The inferred spectral shape and the evolution of the non-thermal component during the outburst, however, are not consistent with the jet origin, but are naturally explained in terms of the hybrid hot flow scenario, where non-thermal electrons emit synchrotron radiation in the OIR band. This implies a close, possibly causal connection between the presence of the hot flow and the compact jet. We find that the non-thermal component is hardening during the hard state at the decaying stage of the outburst, which indicates that the acceleration efficiency is a steep function of radius at low accretion rate.

  3. Irradiation of an Accretion Disc by a Jet: General Properties and Implications for Spin Measurements of Black Holes

    NASA Technical Reports Server (NTRS)

    T.Dauser; Garcia, J.; Wilms, J.; Boeck, M.; Brenneman, L. W.; Falanga, M.; Fukumura, Keigo; Reynolds, C. S.

    2013-01-01

    X-ray irradiation of the accretion disc leads to strong reflection features, which are then broadened and distorted by relativistic effects. We present a detailed, general relativistic approach to model this irradiation for different geometries of the primary X-ray source. These geometries include the standard point source on the rotational axis as well as more jet-like sources, which are radially elongated and accelerating. Incorporating this code in the RELLINE model for relativistic line emission, the line shape for any configuration can be predicted. We study how different irradiation geometries affect the determination of the spin of the black hole. Broad emission lines are produced only for compact irradiating sources situated close to the black hole. This is the only case where the black hole spin can be unambiguously determined. In all other cases the line shape is narrower, which could either be explained by a low spin or an elongated source. We conclude that for those cases and independent of the quality of the data, no unique solution for the spin exists and therefore only a lower limit of the spin value can be given

  4. On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

    NASA Astrophysics Data System (ADS)

    Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

    2016-05-01

    The dynamical response of edge waves under the influence of self-gravity is examined in an idealized two-dimensional model of a proto-stellar disc, characterized in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius r0. The fluid in basic state is prescribed to rotate with a Keplerian profile $\\Omega_k(r)\\sim r^{-3/2}$ modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabilizer irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non- Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density, in addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect . Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

  5. Large-scale magnetic field in the accretion discs of young stars: the influence of magnetic diffusion, buoyancy and Hall effect

    NASA Astrophysics Data System (ADS)

    Khaibrakhmanov, S. A.; Dudorov, A. E.; Parfenov, S. Yu.; Sobolev, A. M.

    2016-09-01

    We investigate the fossil magnetic field in the accretion and protoplanetary discs using the Shakura and Sunyaev approach. The distinguishing feature of this study is the accurate solution of the ionization balance equations and the induction equation with Ohmic diffusion, magnetic ambipolar diffusion, buoyancy and the Hall effect. We consider the ionization by cosmic rays, X-rays and radionuclides, radiative recombinations, recombinations onto dust grains, and also thermal ionization. The buoyancy appears as the additional mechanism of magnetic flux escape in the steady-state solution of the induction equation. Calculations show that Ohmic diffusion and magnetic ambipolar diffusion constraint the generation of the magnetic field inside the `dead' zones. The magnetic field in these regions is quasi-vertical. The buoyancy constraints the toroidal magnetic field strength close to the disc inner edge. As a result, the toroidal and vertical magnetic fields become comparable. The Hall effect is important in the regions close to the borders of the `dead' zones because electrons are magnetized there. The magnetic field in these regions is quasi-radial. We calculate the magnetic field strength and geometry for the discs with accretion rates (10^{-8}-10^{-6}) {M}_{⊙} {yr}^{-1}. The fossil magnetic field geometry does not change significantly during the disc evolution while the accretion rate decreases. We construct the synthetic maps of dust emission polarized due to the dust grain alignment by the magnetic field. In the polarization maps, the `dead' zones appear as the regions with the reduced values of polarization degree in comparison to those in the adjacent regions.

  6. XMM-Newton observations of UW CrB: detection of X-ray bursts and evidence for accretion disc evolution

    NASA Astrophysics Data System (ADS)

    Hakala, Pasi; Ramsay, Gavin; Muhli, Panu; Charles, Phil; Hannikainen, Diana; Mukai, Koji; Vilhu, Osmi

    2005-01-01

    UW CrB (MS 1603+2600) is a peculiar short-period X-ray binary that exhibits extraordinary optical behaviour. The shape of the optical light curve of the system changes drastically from night to night, without any changes in overall brightness. Here we report X-ray observations of UW CrB obtained with XMM-Newton. We find evidence for several X-ray bursts, confirming a neutron star primary. This considerably strengthens the case that UW CrB is an accretion disc corona system located at a distance of at least 5-7 kpc (3-5 kpc above the Galactic plane). The X-ray and Optical Monitor (ultraviolet-optical) light curves show remarkable shape variation from one observing run to another, which we suggest are due to large-scale variations in the accretion disc shape resulting from a warp that periodically obscures the optical and soft X-ray emission. This is also supported by the changes in phase-resolved X-ray spectra.

  7. SAD effects on grantsmanship.

    PubMed

    Lozano, George A

    2015-01-01

    SAD is a state of depression induced by a lack of sufficient sunlight that occurs at high latitudes during the fall and winter. SAD causes people to be risk-adverse. Granting agencies of high latitude countries should time high-risk research competitions so they do not coincide with the SAD months.

  8. Particle acceleration from an inner accretion disc into compact corona and further out: case of an organised magnetic field near a supermassive black hole

    NASA Astrophysics Data System (ADS)

    Karas, Vladimir; Kopacek, Ondrej; Kunneriath, Devaky; Kovar, Jiri; Slany, Petr

    2016-04-01

    Upcoming observational techniques in X-rays and millimeter spectral bands will allow to probe the inner corona of accretion discs near supermassive black holes. Size of this region only a few gravitational radii has been inferred from various circumstantial evidence. To populate ithe region with particles, pair-creation in ergosphere and transport of particles via accretion have been invoked.Electromagnetic fields are a likely agent of acceleration in strong gravity of a rotating black hole. We put forward a scenario with an organised component of the magnetic field near a supermassive black hole. An emergent flow of particles may be induced in a preferentially bi-polar direction. Our mechanism does not seem to be capable of producing ultra-high energy cosmic rays but it does expel particles along unbound trajectories.The mentioned concept is relevant also from a purely theoretical viewpoint of dynamical properties of particle motion in General Relativity, namely, the onset of chaos near a black hole. We conclude that the role of black-hole spin in setting the chaos is more complicated than initially thought (based on http://arxiv.org/abs/1408.2452).

  9. Why Am I So Sad?

    MedlinePlus

    ... Chloe & Nurb Meet The Brain (Movie) Quiz: Do You Need a Flu Shot? Got Homework? Here's Help White House Lunch Recipes Why Am I So Sad? KidsHealth > For Kids > Why Am I So Sad? ... Do Kids Feel Sad About? Are Sad Feelings Normal? How Can You Deal With Sad Feelings? en español ¿Por qué ...

  10. Dynamics of Astrophysical Discs

    NASA Astrophysics Data System (ADS)

    Sellwood, J. A.

    2004-01-01

    Preface; Names and addresses of participants; Conference photograph; 1. Spiral waves in Saturn's rings; 2. Structure of the Uranian rings; 3. Planetary rings: theory; 4. Simulations of light scattering in planetary rings; 5. Accretion discs around young stellar objects and the proto-Sun; 6. The ß Pictoris disc: a planetary rather than a protoplanetary one; 7. Optical polarimetry and thermal imaging of the disc axound ß Pictoris; 8. Observations of discs around protostars and young stars; 9. VLA observations of ammonia towaxd moleculax outflow sources; 10. Derivation of the physical properties of molecular discs by an MEM method; 11. Masers associated with discs around young stars; 12. The nature of polarisation discs axound young stars; 13. The correlation between the main parameters of the interstellar gas (including Salpeter's spectrum of masses) as a result of the development of turbulent Rossby waves; 14. Discs in cataclysmic variables and X-ray binaries; 15. A disc instability model for soft X-ray transients containing black holes; 16. X-ray variability from the accretion disc of NGC 5548; 17. Viscously heated coronae and winds around accretion discs; 18. Optical emission line profiles of symbiotic stars; 19. The effect of formation of Fell in winds confined to discs for luminous stars; 20. Observational evidence for accretion discs in active galactic nuclei; 21. The fuelling of active galactic nuclei by non-axisynlinetric instabilities; 22. The circum-nuclear disc in the Galactic centre; 23. Non-axisymmetric instabilities in thin self-gravitating differentially rotating gaseous discs; 24. Non-linear evolution of non-axisymmetric perturbations in thin self-gravitating gaseous discs; 25. Eccentric gravitational instabilities in nearly Keplerian discs; 26. Gravity mode instabilities in accretion tori; 27. The stability of viscous supersonic shear flows - critical Reynolds numbers and their implications for accretion discs; 28. Asymptotic analysis of overstable

  11. The broad emission-line region: the confluence of the outer accretion disc with the inner edge of the dusty torus

    NASA Astrophysics Data System (ADS)

    Goad, M. R.; Korista, K. T.; Ruff, A. J.

    2012-11-01

    We have investigated the observational characteristics of a class of broad emission line region (BLR) geometries that connect the outer accretion disc with the inner edge of the dusty toroidal obscuring region (TOR). We suggest that the BLR consists of photoionized gas of densities which allow for efficient cooling by ultraviolet (UV)/optical emission lines and of incident continuum fluxes which discourage the formation of grains, and that such gas occupies the range of distance and scale height between the continuum-emitting accretion disc and the dusty TOR. As a first approximation, we assume a population of clouds illuminated by ionizing photons from the central source, with the scale height of the illuminated clouds growing with increasing radial distance, forming an effective surface of a 'bowl'. Observer lines of sight which peer into the bowl lead to a Type 1 active galactic nuclei (AGN) spectrum. We assume that the gas dynamics are dominated by gravity, and we include in this model the effects of transverse Doppler shift (TDS), gravitational redshift (GR) and scale-height-dependent macroturbulence. Our simple model reproduces many of the commonly observed phenomena associated with the central regions of AGN, including (i) the shorter than expected continuum-dust delays (geometry), (ii) the absence of response in the core of the optical recombination lines on short time-scales (geometry/photoionization), (iii) an enhanced redwing response on short time-scales (GR and TDS), (iv) the observed differences between the delays for high- and low-ionization lines (photoionization), (v) identifying one of the possible primary contributors to the observed line widths for near face-on systems even for purely transverse motion (GR and TDS), (vi) a mechanism responsible for producing Lorentzian profiles (especially in the Balmer and Mg II emission lines) in low-inclination systems (turbulence), (vii) the absence of significant continuum-emission-line delays between the

  12. Sad music induces pleasant emotion.

    PubMed

    Kawakami, Ai; Furukawa, Kiyoshi; Katahira, Kentaro; Okanoya, Kazuo

    2013-01-01

    In general, sad music is thought to cause us to experience sadness, which is considered an unpleasant emotion. As a result, the question arises as to why we listen to sad music if it evokes sadness. One possible answer to this question is that we may actually feel positive emotions when we listen to sad music. This suggestion may appear to be counterintuitive; however, in this study, by dividing musical emotion into perceived emotion and felt emotion, we investigated this potential emotional response to music. We hypothesized that felt and perceived emotion may not actually coincide in this respect: sad music would be perceived as sad, but the experience of listening to sad music would evoke positive emotions. A total of 44 participants listened to musical excerpts and provided data on perceived and felt emotions by rating 62 descriptive words or phrases related to emotions on a scale that ranged from 0 (not at all) to 4 (very much). The results revealed that the sad music was perceived to be more tragic, whereas the actual experiences of the participants listening to the sad music induced them to feel more romantic, more blithe, and less tragic emotions than they actually perceived with respect to the same music. Thus, the participants experienced ambivalent emotions when they listened to the sad music. After considering the possible reasons that listeners were induced to experience emotional ambivalence by the sad music, we concluded that the formulation of a new model would be essential for examining the emotions induced by music and that this new model must entertain the possibility that what we experience when listening to music is vicarious emotion.

  13. Sad music induces pleasant emotion

    PubMed Central

    Kawakami, Ai; Furukawa, Kiyoshi; Katahira, Kentaro; Okanoya, Kazuo

    2013-01-01

    In general, sad music is thought to cause us to experience sadness, which is considered an unpleasant emotion. As a result, the question arises as to why we listen to sad music if it evokes sadness. One possible answer to this question is that we may actually feel positive emotions when we listen to sad music. This suggestion may appear to be counterintuitive; however, in this study, by dividing musical emotion into perceived emotion and felt emotion, we investigated this potential emotional response to music. We hypothesized that felt and perceived emotion may not actually coincide in this respect: sad music would be perceived as sad, but the experience of listening to sad music would evoke positive emotions. A total of 44 participants listened to musical excerpts and provided data on perceived and felt emotions by rating 62 descriptive words or phrases related to emotions on a scale that ranged from 0 (not at all) to 4 (very much). The results revealed that the sad music was perceived to be more tragic, whereas the actual experiences of the participants listening to the sad music induced them to feel more romantic, more blithe, and less tragic emotions than they actually perceived with respect to the same music. Thus, the participants experienced ambivalent emotions when they listened to the sad music. After considering the possible reasons that listeners were induced to experience emotional ambivalence by the sad music, we concluded that the formulation of a new model would be essential for examining the emotions induced by music and that this new model must entertain the possibility that what we experience when listening to music is vicarious emotion. PMID:23785342

  14. The star formation history and accretion-disc fraction among the K-type members of the Scorpius-Centaurus OB association

    NASA Astrophysics Data System (ADS)

    Pecaut, Mark J.; Mamajek, Eric E.

    2016-09-01

    We present results of a spectroscopic survey for new K- and M-type members of Scorpius-Centaurus (Sco-Cen), the nearest OB Association (˜100-200 pc). Using an X-ray, proper motion and colour-magnitude selected sample, we obtained spectra for 361 stars, for which we report spectral classifications and Li and Hα equivalent widths. We identified 156 new members of Sco-Cen, and recovered 51 previously published members. We have combined these with previously known members to form a sample of 493 solar-mass (˜0.7-1.3 M⊙) members of Sco-Cen. We investigated the star formation history of this sample, and re-assessed the ages of the massive main-sequence turn-off and the G-type members in all three subgroups. We performed a census for circumstellar discs in our sample using WISE infrared data and find a protoplanetary disc fraction for K-type stars of 4.4^{+1.6}_{-0.9} per cent for Upper Centaurus-Lupus and Lower Centaurus-Crux at ˜16 Myr and 9.0^{+4.0}_{-2.2} per cent for Upper Scorpius at ˜10 Myr. These data are consistent with a protoplanetary disc e-folding time-scale of ˜4-5 Myr for ˜1 M⊙ stars, twice that previously quoted, but consistent with the Bell et al. revised age scale of young clusters. Finally, we construct an age map of Scorpius-Centaurus which clearly reveals substructure consisting of concentrations of younger and older stars. We find evidence for strong age gradients within all three subgroups. None of the subgroups are consistent with being simple, coeval populations which formed in single bursts, but likely represents a multitude of smaller star formation episodes of hundreds to tens of stars each.

  15. Sad Music Moves Those Who Are Empathetic

    MedlinePlus

    ... https://medlineplus.gov/news/fullstory_160987.html Sad Music Moves Those Who Are Empathetic They become engrossed ... 15, 2016 (HealthDay News) -- Many people find sad music relaxing but to those who are very empathetic, ...

  16. Mass Accretion Rate of Rotating Viscous Accretion Flow

    NASA Astrophysics Data System (ADS)

    Park, Myeong-Gu

    2009-11-01

    The mass accretion rate of transonic spherical accretion flow onto compact objects such as black holes is known as the Bondi accretion rate, which is determined only by the density and the temperature of gas at the outer boundary. A rotating accretion flow has angular momentum, which modifies the flow profile from the spherical Bondi flow, and hence its mass accretion rate, but most work on disc accretion has taken the mass flux to be given with the relation between that parameter and external conditions left uncertain. Within the framework of a slim α disk, we have constructed global solutions of the rotating, viscous, hot accretion flow in the Paczyński-Wiita potential and determined its mass accretion rate as a function of density, temperature, and angular momentum of gas at the outer boundary. We find that the low angular momentum flow resembles the spherical Bondi flow and its mass accretion rate approaches the Bondi accretion rate for the same density and temperature at the outer boundary. The high angular momentum flow on the other hand is the conventional hot accretion disk with advection, but its mass accretion rate can be significantly smaller than the Bondi accretion rate with the same boundary conditions. We also find that solutions exist only within a limited range of dimensionless mass accretion rate \\dot{m} ≡ \\dot{M}/\\dot{M}_B, where \\dot{M} is the mass accretion rate and \\dot{M}_B is the Bondi accretion rate: when the temperature at the outer boundary is equal to the virial temperature, solutions exist only for 0.05 ≲ \\dot{m} ≤ 1 when α = 0.01. We also find that the dimensionless mass accretion rate is roughly independent of the radius of the outer boundary but inversely proportional to the angular momentum at the outer boundary and proportional to the viscosity parameter, \\dot{m} ≃ 9.0 α λ^{-1} when 0.1 ≲ \\dot{m} ≲ 1, where the dimensionless angular momentum measure λ ≡ l out/lB is the specific angular momentum of gas at

  17. MASS ACCRETION RATE OF ROTATING VISCOUS ACCRETION FLOW

    SciTech Connect

    Park, Myeong-Gu

    2009-11-20

    The mass accretion rate of transonic spherical accretion flow onto compact objects such as black holes is known as the Bondi accretion rate, which is determined only by the density and the temperature of gas at the outer boundary. A rotating accretion flow has angular momentum, which modifies the flow profile from the spherical Bondi flow, and hence its mass accretion rate, but most work on disc accretion has taken the mass flux to be given with the relation between that parameter and external conditions left uncertain. Within the framework of a slim alpha disk, we have constructed global solutions of the rotating, viscous, hot accretion flow in the Paczynski-Wiita potential and determined its mass accretion rate as a function of density, temperature, and angular momentum of gas at the outer boundary. We find that the low angular momentum flow resembles the spherical Bondi flow and its mass accretion rate approaches the Bondi accretion rate for the same density and temperature at the outer boundary. The high angular momentum flow on the other hand is the conventional hot accretion disk with advection, but its mass accretion rate can be significantly smaller than the Bondi accretion rate with the same boundary conditions. We also find that solutions exist only within a limited range of dimensionless mass accretion rate m-dotident toM-dot/M-dot{sub B}, where M-dot is the mass accretion rate and M-dot{sub B} is the Bondi accretion rate: when the temperature at the outer boundary is equal to the virial temperature, solutions exist only for 0.05approxaccretion rate is roughly independent of the radius of the outer boundary but inversely proportional to the angular momentum at the outer boundary and proportional to the viscosity parameter, m-dotapprox =9.0 alphalambda{sup -1} when 0.1 approx

  18. Using SAD data in Phaser

    SciTech Connect

    Read, Randy J. McCoy, Airlie J.

    2011-04-01

    SAD data can be used in Phaser to solve novel structures, supplement molecular-replacement phase information or identify anomalous scatterers from a final refined model. Phaser is a program that implements likelihood-based methods to solve macromolecular crystal structures, currently by molecular replacement or single-wavelength anomalous diffraction (SAD). SAD phasing is based on a likelihood target derived from the joint probability distribution of observed and calculated pairs of Friedel-related structure factors. This target combines information from the total structure factor (primarily non-anomalous scattering) and the difference between the Friedel mates (anomalous scattering). Phasing starts from a substructure, which is usually but not necessarily a set of anomalous scatterers. The substructure can also be a protein model, such as one obtained by molecular replacement. Additional atoms are found using a log-likelihood gradient map, which shows the sites where the addition of scattering from a particular atom type would improve the likelihood score. An automated completion algorithm adds new sites, choosing optionally among different atom types, adds anisotropic B-factor parameters if appropriate and deletes atoms that refine to low occupancy. Log-likelihood gradient maps can also identify which atoms in a refined protein structure are anomalous scatterers, such as metal or halide ions. These maps are more sensitive than conventional model-phased anomalous difference Fouriers and the iterative completion algorithm is able to find a significantly larger number of convincing sites.

  19. P-mode oscillation on slim discs

    NASA Astrophysics Data System (ADS)

    Xue, Li; Lu, Ju-Fu

    2016-02-01

    We numerically investigate the thermally unstable accretion discs around spinning black holes with different spins. We adopted an additional evolutionary viscosity equation to replace the standard alpha-prescription based on the results of two MHD simulations. We find an interesting oscillation when accretion switches to slim disc mode. The oscillation arises from the sonic point of accretion flow and propagates outwards. We mimic the bolometric light-curve and find a series of harmonics on its power spectrum. The frequency ratio of those harmonics is a regular integer series. The lowest frequency of the harmonics is identical to the prediction of trapped p-mode in QPO theory.

  20. Using SAD data in Phaser.

    PubMed

    Read, Randy J; McCoy, Airlie J

    2011-04-01

    Phaser is a program that implements likelihood-based methods to solve macromolecular crystal structures, currently by molecular replacement or single-wavelength anomalous diffraction (SAD). SAD phasing is based on a likelihood target derived from the joint probability distribution of observed and calculated pairs of Friedel-related structure factors. This target combines information from the total structure factor (primarily non-anomalous scattering) and the difference between the Friedel mates (anomalous scattering). Phasing starts from a substructure, which is usually but not necessarily a set of anomalous scatterers. The substructure can also be a protein model, such as one obtained by molecular replacement. Additional atoms are found using a log-likelihood gradient map, which shows the sites where the addition of scattering from a particular atom type would improve the likelihood score. An automated completion algorithm adds new sites, choosing optionally among different atom types, adds anisotropic B-factor parameters if appropriate and deletes atoms that refine to low occupancy. Log-likelihood gradient maps can also identify which atoms in a refined protein structure are anomalous scatterers, such as metal or halide ions. These maps are more sensitive than conventional model-phased anomalous difference Fouriers and the iterative completion algorithm is able to find a significantly larger number of convincing sites. PMID:21460452

  1. The formation of discs in clusters

    NASA Astrophysics Data System (ADS)

    Clark, Paul C.

    2010-11-01

    We review the properties of the discs that form around ‘sink particles’ in smoothed particle hydrodynamics (SPH) simulations of cluster formation, similar to those of Bate et al. (2003) and Bonnell et al. (2004), and compare them to the observed properties of discs in nearby star-forming regions. Contrary to previous suggestions, discs can form and survive in such an environment, despite the chaotic effects of competitive accretion. We find the discs are typically massive, with ratios of disc mass to central object mass of around 0.1, or higher, being typical. Naturally, the evolution of these discs is dominated by gravitational torques, and the more massive examples exhibit strong m=2 spiral modes. We also find that they can continuously grow over a period of 100,000 years, provided the central object is a single sink particle and the local density of sink particles is low. Discs that form around sink particles in the very centres of clusters tend to be shorter lived, but a single star can lose and gain a disc several times during the main accretion phase. However due to the nature of the turbulence in the cluster, the disc orientation can change dramatically over this time period, since disc-sink systems can accrete from counter-rotating envelopes. Since the competitive accretion process brings in material from large distances, the associated angular momentum can be higher than one would expect for an isolated star formation model. As such, we find that the discs are typically several hundred of AUs in extent, with the largest keplerian structures having radii of ~ 2000AU.

  2. Friendship and the Socialization of Sadness

    ERIC Educational Resources Information Center

    Tillery, Rachel; Cohen, Robert; Parra, Gilbert R.; Kitzmann, Katherine M.; Sharp, Katianne M. Howard

    2015-01-01

    Children's ability to manage the expression of sadness is critical to their development and adjustment. Although parents have been the primary focus of research examining sadness socialization, many acknowledge the influence of other agents such as children's peers. The present research evaluated one type of emotion socialization--reactions to…

  3. Proto-planetary disc evolution and dispersal

    NASA Astrophysics Data System (ADS)

    Rosotti, Giovanni Pietro

    2015-05-01

    Planets form from gas and dust discs in orbit around young stars. The timescale for planet formation is constrained by the lifetime of these discs. The properties of the formed planetary systems depend thus on the evolution and final dispersal of the discs, which is the main topic of this thesis. Observations reveal the existence of a class of discs called "transitional", which lack dust in their inner regions. They are thought to be the last stage before the complete disc dispersal, and hence they may provide the key to understanding the mechanisms behind disc evolution. X-ray photoevaporation and planet formation have been studied as possible physical mechanisms responsible for the final dispersal of discs. However up to now, these two phenomena have been studied separately, neglecting any possible feedback or interaction. In this thesis we have investigated what is the interplay between these two processes. We show that the presence of a giant planet in a photo-evaporating disc can significantly shorten its lifetime, by cutting the inner regions from the mass reservoir in the exterior of the disc. This mechanism produces transition discs that for a given mass accretion rate have larger holes than in models considering only X-ray photo-evaporation, constituting a possible route to the formation of accreting transition discs with large holes. These discs are found in observations and still constitute a puzzle for the theory. Inclusion of the phenomenon called "thermal sweeping", a violent instability that can destroy a whole disc in as little as 10 4 years, shows that the outer disc left can be very short-lived (depending on the X-ray luminosity of the star), possibly explaining why very few non accreting transition discs are observed. However the mechanism does not seem to be efficient enough to reconcile with observations. In this thesis we also show that X-ray photo-evaporation naturally explains the observed correlation between stellar masses and accretion

  4. Accretion on to Magnetic White Dwarfs

    NASA Astrophysics Data System (ADS)

    Wickramasinghe, Dayal

    2014-01-01

    The Magnetic Cataclysmic Variables (MCVs) are close interacting binaries where mass is transferred from a late type secondary star to a magnetic white dwarf. Two modes of accretion can be identified depending on the strength of the magnetic field, the mass transfer rate and orbital parameters. (a) Disced Accretion: In the Intermediate polars (IPs), the mass transfer stream circularises and forms an accretion disc. Material couples on to field lines in a narrow inner transition region where the velocity in the orbital plane changes from Keplerian to co-rotation (b) Discless Accretion: In the polars, the accretion stream is disrupted by the magnetic field before it can circularise. Material couples on to field lines via an inner transition region where the velocity changes from essentially free fall to co-rotation. The polars have no counterparts in neutron star systems and their study provides unique insights into the complex nature of the magnetospheric boundary. The observed properties of accretion shocks at the white dwarf surface such as the anomalous soft-X-ray excess and its time variability provide strong support for the hypothesis that under certain circumstances the field channelled funnel flow is "blobby". This has been attributed to interchange instabilities such as the Magnetic Rayleigh-Taylor instability in the shocked gas at the stream-magnetosphere boundary where the stream fragments into discrete clumps of gas. As the clumps penetrate into the magnetosphere, they are shredded into smaller mass blobs via the Kelvin-Helmholtz instability that then couple on to field lines over an extended inner transition region in the orbital plane. The more massive blobs penetrate deep into the photosphere of the white dwarf releasing their energy as a reprocessed soft-X-ray black body component. Although similar instabilities are expected in the inner transition region in disced accretion albeit on a different scale there has been no direct observational evidence

  5. On the evolution of the protolunar disc.

    PubMed

    Ward, William R

    2014-09-13

    The structure and viscous evolution of a post-impact, protolunar disc is examined. The equations for a silicate disc in two-phase (vapour-liquid) equilibrium are employed to derive an analytical solution to vertical structure. Both a vertically mixed phase disc and a stratified disc, where a magma layer exists in the mid-plane surrounded by a vapour reservoir, are considered. The former largely reproduces the low gas mass fraction, x≪1, profiles of the disc described in earlier literature that proposed that the disc would hover on the brink of gravitational instability. In the latter, the vapour layer has x∼1 and is generally gravitationally stable, while the magma layer is vigorously unstable. The viscous evolution of the stratified model is then explored. Initially, the disc quickly settles to a quasi-steady state with a vapour reservoir containing the majority of the disc mass. The magma layer viscously spreads on a time scale of approximately 3-4 years, during which vapour continuously condenses into droplets that settle to the mid-plane, maintaining the magma surface density in spite of disc spreading. Material flowing inwards is accreted by the Earth; material flowing outwards past the Roche boundary can become incorporated into accreting moonlets. This evolution persists until the vapour reservoir is depleted in approximately 50-100 years, depending on its initial mass. PMID:25114314

  6. Jet and disc luminosities in tidal disruption events

    NASA Astrophysics Data System (ADS)

    Piran, Tsvi; Sądowski, Aleksander; Tchekhovskoy, Alexander

    2015-10-01

    Tidal disruption events (TDEs) explore the whole range of accretion rates and configurations. A challenging question is what the corresponding light curves of these events are. We explore numerically the disc luminosity and the conditions within the inner region of the disc using a fully general relativistic slim disc model. Those conditions determine the magnitude of the magnetic field that engulfs the black hole and this, in turn, determines the Blandford-Znajek jet power. We estimate this power in two different ways and show that they are self-consistent. We find, as expected earlier from analytic arguments , that neither the disc luminosity nor the jet power follows the accretion rate throughout the disruption event. The disc luminosity varies only logarithmically with the accretion rate at super-Eddington luminosities. The jet power follows initially the accretion rate but remains constant after the transition from super- to sub-Eddington. At lower accretion rates at the end of the magnetically arrested disc (MAD) phase, the disc becomes thin and the jet may stop altogether. These new estimates of the jet power and disc luminosity that do not simply follow the mass fallback rate should be taken into account when searching for TDEs and analysing light curves of TDE candidates. Identification of some of the above-mentioned transitions may enable us to estimate better TDE parameters.

  7. Sudden Arrhythmia Death Syndromes (SADS) Foundation

    MedlinePlus

    ... SADS Foundation and John Hopkins Hospital Division of Cardiology are hosting a family support and educational meeting ... Baltimore/DC area families with cardiac arrhythmias. Sports Cardiology & Sudden Cardiac Arrest in the Young Conference 01/ ...

  8. Magnetic cataclysmic variable accretion flows

    NASA Astrophysics Data System (ADS)

    Norton, A. J.; Butters, O. W.; Parker, T. L.; Wynn, G. A.

    2007-08-01

    We have used a magnetic accretion model to investigate the accretion flows of magnetic cataclysmic variables (mCVs) throughout a range of parameter space. The results of our numerical simulations demonstrate that broadly four types of flow are possible: discs, streams, rings and propellers. We show that the equilibrium spin periods in asynchronous mCVs, for a given orbital period and magnetic moment, occur where the flow changes from a type characterised by spin-up (i.e. disc or stream) to one characterised by spin-down (i.e. propeller or ring). `Triple points' occur in the plane of spin-to-orbital period ratio versus magnetic moment, at which stream-disc-propeller flows or stream-ring-propeller flows can co-exist. The first of these is identified as corresponding to when the corotation radius is equal to the circularisation radius, and the second as where the corotation radius is equal to the distance from white dwarf to the L1 point. If mCVs are accreting at their equilibrium spin rates, then for a mass ratio of 0.5, those with Pspin/Porb <~ 0.10 will be disc-like, those with 0.10 <~ Pspin/Porb <~ 0.55 will be stream-like, and those with Pspin/Porb ~ 0.55 will be ring-like. In each case, some material is also lost from the binary in order to maintain angular momentum balance. The spin to orbital period ratio at which the systems transition between these flow types decreases as the mass ratio of the stellar components increases, and vice versa.

  9. Accretion characteristics in intermediate polars

    NASA Astrophysics Data System (ADS)

    Parker, Tracey Louise

    This thesis concerns the class of interacting binaries known as intermediate polars (IPs). These are semi-detached magnetic cataclysmic variable systems in which a red dwarf secondary transfers material via Roche lobe overflow onto a white dwarf (WD). The magnetic field of the white dwarf (~10 6 to 10 7 Gauss) plays an important part in determining the type of accretion flow from the secondary. In chapter 1, I discuss binary systems in general, moving on to a more in depth look at Intermediate polars (IPs), their geometry and characteristics, ending with a brief look at all known IPs to date. In the first part of the thesis I present an analysis of the X-ray lightcurves in 16 IPs in order to examine the possible cause of the orbital modulation. I show that X-ray orbital modulation is widespread amongst IN, but not ubiquitous. The orbital modulation is most likely due to photoelectric absorption in material at the edge of the accretion disk. Assuming a random distribution of inclination angles, the fact that such a modulation is seen in seven systems out of sixteen studied (plus two eclipsing systems) implies that modulations are visible at inclination angles in excess of 60°. It is also apparent that these modulations can appear and disappear on timescales of ~years or months in an individual system, which may be evidence for precessing, tilted accretion disks. In the second half of the thesis I use a particle hydrodynamical code known as HyDisc, to investigate the accretion flows in IPs, as a function of parameter space for two dipole models. One where we assume that the density and size scale of the blobs being accreted are constant which we refer to as the n 6 model, and the other where the size scale and density of the accreted blobs are not constant referred to as the n 3 model. I show that the accretion flow can take the form of an accretion disk, accretion stream, propeller accretion and ring accretion for the n 3 model and stream and disk accretion in the

  10. The slimming effect of advection on black-hole accretion flows

    NASA Astrophysics Data System (ADS)

    Lasota, J.-P.; Vieira, R. S. S.; Sadowski, A.; Narayan, R.; Abramowicz, M. A.

    2016-03-01

    Context. At super-Eddington rates accretion flows onto black holes have been described as slim (aspect ratio H/R ≲ 1) or thick (H/R> 1) discs, also known as tori or (Polish) doughnuts. The relation between the two descriptions has never been established, but it was commonly believed that at sufficiently high accretion rates slim discs inflate, becoming thick. Aims: We wish to establish under what conditions slim accretion flows become thick. Methods: We use analytical equations, numerical 1 + 1 schemes, and numerical radiative MHD codes to describe and compare various accretion flow models at very high accretion rates. Results: We find that the dominant effect of advection at high accretion rates precludes slim discs becoming thick. Conclusions: At super-Eddington rates accretion flows around black holes can always be considered slim rather than thick.

  11. Cloning and functional characterization of SAD genes in potato.

    PubMed

    Li, Fei; Bian, Chun Song; Xu, Jian Fei; Pang, Wan Fu; Liu, Jie; Duan, Shao Guang; Lei, Zun-Guo; Jiwan, Palta; Jin, Li-Ping

    2015-01-01

    Stearoyl-acyl carrier protein desaturase (SAD), locating in the plastid stroma, is an important fatty acid biosynthetic enzyme in higher plants. SAD catalyzes desaturation of stearoyl-ACP to oleyl-ACP and plays a key role in determining the homeostasis between saturated fatty acids and unsaturated fatty acids, which is an important player in cold acclimation in plants. Here, four new full-length cDNA of SADs (ScoSAD, SaSAD, ScaSAD and StSAD) were cloned from four Solanum species, Solanum commersonii, S. acaule, S. cardiophyllum and S. tuberosum, respectively. The ORF of the four SADs were 1182 bp in length, encoding 393 amino acids. A sequence alignment indicated 13 amino acids varied among the SADs of three wild species. Further analysis showed that the freezing tolerance and cold acclimation capacity of S. commersonii are similar to S. acaule and their SAD amino acid sequences were identical but differed from that of S. cardiophyllum, which is sensitive to freezing. Furthermore, the sequence alignments between StSAD and ScoSAD indicated that only 7 different amino acids at residues were found in SAD of S. tuberosum (Zhongshu8) against the protein sequence of ScoSAD. A phylogenetic analysis showed the three wild potato species had the closest genetic relationship with the SAD of S. lycopersicum and Nicotiana tomentosiformis but not S. tuberosum. The SAD gene from S. commersonii (ScoSAD) was cloned into multiple sites of the pBI121 plant binary vector and transformed into the cultivated potato variety Zhongshu 8. A freeze tolerance analysis showed overexpression of the ScoSAD gene in transgenic plants significantly enhanced freeze tolerance in cv. Zhongshu 8 and increased their linoleic acid content, suggesting that linoleic acid likely plays a key role in improving freeze tolerance in potato plants. This study provided some new insights into how SAD regulates in the freezing tolerance and cold acclimation in potato. PMID:25825911

  12. Gamma-burst emission from neutron-star accretion

    NASA Technical Reports Server (NTRS)

    Colgate, S. A.; Petschek, A. G.; Sarracino, R.

    1983-01-01

    A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without a magnetic field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge separation is required to drag electrons into the star with the nuclei against the flux of photons leaking out through the accreting matter. The photon number is not increased substantially by Bremsstrahlung or any other process. It is suggested that instability in an accretion disc might provide the infalling matter required.

  13. The role of thermodynamics in disc fragmentation

    NASA Astrophysics Data System (ADS)

    Stamatellos, Dimitris; Whitworth, Anthony P.

    2009-12-01

    Thermodynamics play an important role in determining the way a protostellar disc fragments to form planets, brown dwarfs and low-mass stars. We explore the effect that different treatments of radiative transfer have in simulations of fragmenting discs. Three prescriptions for the radiative transfer are used: (i) the diffusion approximation of Stamatellos et al.; (ii) the barotropic equation of state (EOS) of Goodwin et al. and (iii) the barotropic EOS of Bate et al. The barotropic approximations capture the general evolution of the density and temperature at the centre of each proto-fragment but (i) they do not make any adjustments for particular circumstances of a proto-fragment forming in the disc and (ii) they do not take into account thermal inertia effects that are important for fast-forming proto-fragments in the outer disc region. As a result, the number of fragments formed in the disc and their properties are different, when a barotropic EOS is used. This is important not only for disc studies but also for simulations of collapsing turbulent clouds, as in many cases in such simulations stars form with discs that subsequently fragment. We also examine the difference in the way proto-fragments condense out in the disc at different distances from the central star using the diffusion approximation and following the collapse of each proto-fragment until the formation of the second core (ρ ~= 10-3gcm-3). We find that proto-fragments forming closer to the central star tend to form earlier and evolve faster from the first to the second core than proto-fragments forming in the outer disc region. The former have a large pool of material in the inner disc region that they can accrete from and grow in mass. The latter accrete more slowly and they are hotter because they generally form in a quick abrupt event.

  14. From birth to death of protoplanetary discs: modelling their formation, evolution and dispersal

    NASA Astrophysics Data System (ADS)

    Kimura, Shigeo S.; Kunitomo, Masanobu; Takahashi, Sanemichi Z.

    2016-09-01

    The formation, evolution and dispersal processes of protoplanetary discs are investigated and the disc lifetime is estimated. The gravitational collapse of a pre-stellar core forms both a central star and a protoplanetary disc. The central star grows by accretion from the disc and irradiation by the central star heats up the disc and generates a thermal wind, which results in the disc's dispersal. Using the one-dimensional diffusion equation, we calculate the evolution of protoplanetary discs numerically. To calculate the disc evolution from formation to dispersal, we add source and sink terms that represent gas accretion from pre-stellar cores and photoevaporation, respectively. We find that the disc lifetimes of typical pre-stellar cores are around 2-4 million years (Myr). A pre-stellar core with high angular momentum forms a larger disc with a long lifetime, while a disc around an X-ray-luminous star has a short lifetime. Integrating disc lifetimes under various masses and angular velocities of pre-stellar cores and X-ray luminosities of young stellar objects, we obtain the disc fraction at a given stellar age and mean lifetime of the disc. Our model indicates that the mean lifetime of a protoplanetary disc is 3.7 Myr, which is consistent with the observational estimate from young stellar clusters. We also find that the dispersion of X-ray luminosity is needed to reproduce the observed disc fraction.

  15. Entrepreneurialism at the University of Novi Sad

    ERIC Educational Resources Information Center

    Stankovic, Fuada

    2006-01-01

    What does being an entrepreneurial university mean? The University of Novi Sad in Serbia is taken as an example of how one University in a transition country, which was lacking tradition in entrepreneurial practices, is striving to become an entrepreneurial university. Examples of new practices are also described such as the establishment of a…

  16. The paradox of music-evoked sadness: an online survey.

    PubMed

    Taruffi, Liila; Koelsch, Stefan

    2014-01-01

    This study explores listeners' experience of music-evoked sadness. Sadness is typically assumed to be undesirable and is therefore usually avoided in everyday life. Yet the question remains: Why do people seek and appreciate sadness in music? We present findings from an online survey with both Western and Eastern participants (N = 772). The survey investigates the rewarding aspects of music-evoked sadness, as well as the relative contribution of listener characteristics and situational factors to the appreciation of sad music. The survey also examines the different principles through which sadness is evoked by music, and their interaction with personality traits. Results show 4 different rewards of music-evoked sadness: reward of imagination, emotion regulation, empathy, and no "real-life" implications. Moreover, appreciation of sad music follows a mood-congruent fashion and is greater among individuals with high empathy and low emotional stability. Surprisingly, nostalgia rather than sadness is the most frequent emotion evoked by sad music. Correspondingly, memory was rated as the most important principle through which sadness is evoked. Finally, the trait empathy contributes to the evocation of sadness via contagion, appraisal, and by engaging social functions. The present findings indicate that emotional responses to sad music are multifaceted, are modulated by empathy, and are linked with a multidimensional experience of pleasure. These results were corroborated by a follow-up survey on happy music, which indicated differences between the emotional experiences resulting from listening to sad versus happy music. This is the first comprehensive survey of music-evoked sadness, revealing that listening to sad music can lead to beneficial emotional effects such as regulation of negative emotion and mood as well as consolation. Such beneficial emotional effects constitute the prime motivations for engaging with sad music in everyday life.

  17. The Paradox of Music-Evoked Sadness: An Online Survey

    PubMed Central

    Taruffi, Liila; Koelsch, Stefan

    2014-01-01

    This study explores listeners’ experience of music-evoked sadness. Sadness is typically assumed to be undesirable and is therefore usually avoided in everyday life. Yet the question remains: Why do people seek and appreciate sadness in music? We present findings from an online survey with both Western and Eastern participants (N = 772). The survey investigates the rewarding aspects of music-evoked sadness, as well as the relative contribution of listener characteristics and situational factors to the appreciation of sad music. The survey also examines the different principles through which sadness is evoked by music, and their interaction with personality traits. Results show 4 different rewards of music-evoked sadness: reward of imagination, emotion regulation, empathy, and no “real-life” implications. Moreover, appreciation of sad music follows a mood-congruent fashion and is greater among individuals with high empathy and low emotional stability. Surprisingly, nostalgia rather than sadness is the most frequent emotion evoked by sad music. Correspondingly, memory was rated as the most important principle through which sadness is evoked. Finally, the trait empathy contributes to the evocation of sadness via contagion, appraisal, and by engaging social functions. The present findings indicate that emotional responses to sad music are multifaceted, are modulated by empathy, and are linked with a multidimensional experience of pleasure. These results were corroborated by a follow-up survey on happy music, which indicated differences between the emotional experiences resulting from listening to sad versus happy music. This is the first comprehensive survey of music-evoked sadness, revealing that listening to sad music can lead to beneficial emotional effects such as regulation of negative emotion and mood as well as consolation. Such beneficial emotional effects constitute the prime motivations for engaging with sad music in everyday life. PMID:25330315

  18. Dynamics of core accretion

    NASA Astrophysics Data System (ADS)

    Nelson, Andrew F.; Ruffert, Maximilian

    2013-02-01

    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 however, as defined by locally isothermal or

  19. 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

  20. 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

  1. Enjoying Sad Music: Paradox or Parallel Processes?

    PubMed

    Schubert, Emery

    2016-01-01

    Enjoyment of negative emotions in music is seen by many as a paradox. This article argues that the paradox exists because it is difficult to view the process that generates enjoyment as being part of the same system that also generates the subjective negative feeling. Compensation theories explain the paradox as the compensation of a negative emotion by the concomitant presence of one or more positive emotions. But compensation brings us no closer to explaining the paradox because it does not explain how experiencing sadness itself is enjoyed. The solution proposed is that an emotion is determined by three critical processes-labeled motivational action tendency (MAT), subjective feeling (SF) and Appraisal. For many emotions the MAT and SF processes are coupled in valence. For example, happiness has positive MAT and positive SF, annoyance has negative MAT and negative SF. However, it is argued that in an aesthetic context, such as listening to music, emotion processes can become decoupled. The decoupling is controlled by the Appraisal process, which can assess if the context of the sadness is real-life (where coupling occurs) or aesthetic (where decoupling can occur). In an aesthetic context sadness retains its negative SF but the aversive, negative MAT is inhibited, leaving sadness to still be experienced as a negative valanced emotion, while contributing to the overall positive MAT. Individual differences, mood and previous experiences mediate the degree to which the aversive aspects of MAT are inhibited according to this Parallel Processing Hypothesis (PPH). The reason for hesitancy in considering or testing PPH, as well as the preponderance of research on sadness at the exclusion of other negative emotions, are discussed. PMID:27445752

  2. Enjoying Sad Music: Paradox or Parallel Processes?

    PubMed

    Schubert, Emery

    2016-01-01

    Enjoyment of negative emotions in music is seen by many as a paradox. This article argues that the paradox exists because it is difficult to view the process that generates enjoyment as being part of the same system that also generates the subjective negative feeling. Compensation theories explain the paradox as the compensation of a negative emotion by the concomitant presence of one or more positive emotions. But compensation brings us no closer to explaining the paradox because it does not explain how experiencing sadness itself is enjoyed. The solution proposed is that an emotion is determined by three critical processes-labeled motivational action tendency (MAT), subjective feeling (SF) and Appraisal. For many emotions the MAT and SF processes are coupled in valence. For example, happiness has positive MAT and positive SF, annoyance has negative MAT and negative SF. However, it is argued that in an aesthetic context, such as listening to music, emotion processes can become decoupled. The decoupling is controlled by the Appraisal process, which can assess if the context of the sadness is real-life (where coupling occurs) or aesthetic (where decoupling can occur). In an aesthetic context sadness retains its negative SF but the aversive, negative MAT is inhibited, leaving sadness to still be experienced as a negative valanced emotion, while contributing to the overall positive MAT. Individual differences, mood and previous experiences mediate the degree to which the aversive aspects of MAT are inhibited according to this Parallel Processing Hypothesis (PPH). The reason for hesitancy in considering or testing PPH, as well as the preponderance of research on sadness at the exclusion of other negative emotions, are discussed.

  3. Enjoying Sad Music: Paradox or Parallel Processes?

    PubMed Central

    Schubert, Emery

    2016-01-01

    Enjoyment of negative emotions in music is seen by many as a paradox. This article argues that the paradox exists because it is difficult to view the process that generates enjoyment as being part of the same system that also generates the subjective negative feeling. Compensation theories explain the paradox as the compensation of a negative emotion by the concomitant presence of one or more positive emotions. But compensation brings us no closer to explaining the paradox because it does not explain how experiencing sadness itself is enjoyed. The solution proposed is that an emotion is determined by three critical processes—labeled motivational action tendency (MAT), subjective feeling (SF) and Appraisal. For many emotions the MAT and SF processes are coupled in valence. For example, happiness has positive MAT and positive SF, annoyance has negative MAT and negative SF. However, it is argued that in an aesthetic context, such as listening to music, emotion processes can become decoupled. The decoupling is controlled by the Appraisal process, which can assess if the context of the sadness is real-life (where coupling occurs) or aesthetic (where decoupling can occur). In an aesthetic context sadness retains its negative SF but the aversive, negative MAT is inhibited, leaving sadness to still be experienced as a negative valanced emotion, while contributing to the overall positive MAT. Individual differences, mood and previous experiences mediate the degree to which the aversive aspects of MAT are inhibited according to this Parallel Processing Hypothesis (PPH). The reason for hesitancy in considering or testing PPH, as well as the preponderance of research on sadness at the exclusion of other negative emotions, are discussed. PMID:27445752

  4. Do you remember your sad face? The roles of negative cognitive style and sad mood.

    PubMed

    Caudek, Corrado; Monni, Alessandra

    2013-01-01

    We studied the effects of negative cognitive style, sad mood, and facial affect on the self-face advantage in a sample of 66 healthy individuals (mean age 26.5 years, range 19-47 years). The sample was subdivided into four groups according to inferential style and responsivity to sad mood induction. Following a sad mood induction, we examined the effect on working memory of an incidental association between facial affect, facial identity, and head-pose orientation. Overall, head-pose recognition was more accurate for the self-face than for nonself face (self-face advantage, SFA). However, participants high in negative cognitive style who experienced higher levels of sadness displayed a stronger SFA for sad expressions than happy expressions. The remaining participants displayed an opposite bias (a stronger SFA for happy expressions than sad expressions), or no bias. These findings highlight the importance of trait-vulnerability status in the working memory biases related to emotional facial expressions.

  5. Use of the SADS diagnostic interview in evaluating legal insanity.

    PubMed

    Rogers, R; Thatcher, A; Cavanaugh, J L

    1984-11-01

    Examined clinical usefulness of the SADS diagnostic interview in evaluations of criminal responsibility. Findings, based on 78 SADS evaluations from a specialized forensic clinic, indicated that SADS successfully differentiated between sane and insane evaluatees. These differences were found primilarily in the severity of psychotic symptoms and overall level of psychological impairment. In addition, preliminary data on institutionalized and outpatient Ss suggested the potential applicability of the SADS for assessing the general psychological functioning of insane patients in treatment.

  6. Unresolved Anger and Sadness: Identifying Vocal Acoustical Correlates

    ERIC Educational Resources Information Center

    Rochman, Daniel; Diamond, Gary M.; Amir, Ofer

    2008-01-01

    The authors conducted 2 studies to identify the vocal acoustical correlates of unresolved anger and sadness among women reporting unresolved anger toward an attachment figure. In Study 1, participants (N = 17) were induced to experience and express anger then sadness or sadness then anger. In Study 2, a 2nd group of participants (N = 22) underwent…

  7. Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances

    NASA Astrophysics Data System (ADS)

    Snaith, O.; Haywood, M.; Di Matteo, P.; Lehnert, M. D.; Combes, F.; Katz, D.; Gómez, A.

    2015-06-01

    We develop a chemical evolution model to study the star formation history of the Milky Way. Our model assumes that the Milky Way has formed from a closed-box-like system in the inner regions, while the outer parts of the disc have experienced some accretion. Unlike the usual procedure, we do not fix the star formation prescription (e.g. Kennicutt law) to reproduce the chemical abundance trends. Instead, we fit the abundance trends with age to recover the star formation history of the Galaxy. Our method enables us to recover the star formation history of the Milky Way in the first Gyrs with unprecedented accuracy in the inner (R < 7-8 kpc) and outer (R > 9-10 kpc) discs, as sampled in the solar vicinity. We show that half the stellar mass formed during the thick-disc phase in the inner galaxy during the first 4-5 Gyr. This phase was followed by a significant dip in star formation activity (at 8-9 Gyr) and a period of roughly constant lower-level star formation for the remaining 8 Gyr. The thick-disc phase has produced as many metals in 4 Gyr as the thin-disc phase in the remaining 8 Gyr. Our results suggest that a closed-box model is able to fit all the available constraints in the inner disc. A closed-box system is qualitatively equivalent to a regime where the accretion rate maintains a high gas fraction in the inner disc at high redshift. In these conditions the SFR is mainly governed by the high turbulence of the interstellar medium. By z ~ 1 it is possible that most of the accretion takes place in the outer disc, while the star formation activity in the inner disc is mostly sustained by the gas that is not consumed during the thick-disc phase and the continuous ejecta from earlier generations of stars. The outer disc follows a star formation history very similar to that of the inner disc, although initiated at z ~ 2, about 2 Gyr before the onset of the thin-disc formation in the inner disc.

  8. The inner cavity of the circumnuclear disc

    NASA Astrophysics Data System (ADS)

    Blank, M.; Morris, M. R.; Frank, A.; Carroll-Nellenback, J. J.; Duschl, W. J.

    2016-06-01

    The circumnuclear disc (CND) orbiting the Galaxy's central black hole is a reservoir of material that can ultimately provide energy through accretion, or form stars in the presence of the black hole, as evidenced by the stellar cluster that is presently located at the CND's centre. In this paper, we report the results of a computational study of the dynamics of the CND. The results lead us to question two paradigms that are prevalent in previous research on the Galactic Centre. The first is that the disc's inner cavity is maintained by the interaction of the central stellar cluster's strong winds with the disc's inner rim, and secondly, that the presence of unstable clumps in the disc implies that the CND is a transient feature. Our simulations show that, in the absence of a magnetic field, the interaction of the wind with the inner disc rim actually leads to a filling of the inner cavity within a few orbital time-scales, contrary to previous expectations. However, including the effects of magnetic fields stabilizes the inner disc rim against rapid inward migration. Furthermore, this interaction causes instabilities that continuously create clumps that are individually unstable against tidal shearing. Thus the occurrence of such unstable clumps does not necessarily mean that the disc is itself a transient phenomenon. The next steps in this investigation are to explore the effect of the magnetorotational instability on the disc evolution and to test whether the results presented here persist for longer time-scales than those considered here.

  9. The Origin and Evolution of Transition Discs: Successes, Problems, and Open Questions

    NASA Astrophysics Data System (ADS)

    Owen, James E.

    2016-02-01

    Transition discs are protoplanetary discs that show evidence for large holes or wide gaps (with widths comparable to their radii) in their dust component. These discs could be giving us clues about the disc destruction mechanism or hints about the location and time-scales for the formation of planets. However, at the moment there remain key gaps in our theoretical understanding. The vast majority of transition discs are accreting onto their central stars, indicating that-at least close to the star-dust has been depleted from the gas by a very large amount. In this review, we discuss evidence for two distinct populations of transition discs: mm-faint-those with low mm-fluxes, small holes (≲ 10 AU), and low accretion rates (~ 10-10 - 10-9 M⊙ yr-1) and mm-bright-discs with large mm-fluxes, large holes (≳ 20 AU), and high accretion rates ~ 10-8 M⊙ yr-1. MM-faint transition discs are consistent with what would naively be expected from a disc undergoing dispersal; however, mm-bright discs are not, and are likely to be rare and long-lived objects. We discuss the two commonly proposed mechanisms for creating transition discs: photoevaporation and planet-disc interactions, with a particular emphasis on how they would evolve in these models, comparing these predictions to the observed population. More theoretical work on explaining the lack of optically thick, non-accreting transition discs is required in both the photoevaporation and planetary hypothesis, before we can start to use transition discs to constrain models of planet formation. Finally, we suggest that the few discs with primordial looking spectral energy distribution, but serendipitously imaged showing large cavities in the mm (e.g. MWC758 and WSB 60) may represent a hidden population of associated objects. Characterising and understanding how these objects fit into the overall paradigm may allow us to unravel the mystery of transition discs.

  10. Spacetime Average Density (SAD) cosmological measures

    SciTech Connect

    Page, Don N.

    2014-11-01

    The measure problem of cosmology is how to obtain normalized probabilities of observations from the quantum state of the universe. This is particularly a problem when eternal inflation leads to a universe of unbounded size so that there are apparently infinitely many realizations or occurrences of observations of each of many different kinds or types, making the ratios ambiguous. There is also the danger of domination by Boltzmann Brains. Here two new Spacetime Average Density (SAD) measures are proposed, Maximal Average Density (MAD) and Biased Average Density (BAD), for getting a finite number of observation occurrences by using properties of the Spacetime Average Density (SAD) of observation occurrences to restrict to finite regions of spacetimes that have a preferred beginning or bounce hypersurface. These measures avoid Boltzmann brain domination and appear to give results consistent with other observations that are problematic for other widely used measures, such as the observation of a positive cosmological constant.

  11. Binary accretion rates: dependence on temperature and mass ratio

    NASA Astrophysics Data System (ADS)

    Young, M. D.; Clarke, C. J.

    2015-09-01

    We perform a series of 2D smoothed particle hydrodynamics simulations of gas accretion on to binaries via a circumbinary disc, for a range of gas temperatures and binary mass ratios (q). We show that increasing the gas temperature increases the accretion rate on to the primary for all values of the binary mass ratio: for example, for q = 0.1 and a fixed binary separation, an increase of normalized sound speed by a factor of 5 (from our `cold' to `hot' simulations) changes the fraction of the accreted gas that flows on to the primary from 10 to ˜40 per cent. We present a simple parametrization for the average accretion rate of each binary component accurate to within a few per cent and argue that this parametrization (rather than those in the literature based on warmer simulations) is relevant to supermassive black hole accretion and all but the widest stellar binaries. We present trajectories for the growth of q during circumbinary disc accretion and argue that the period distribution of stellar `twin' binaries is strong evidence for the importance of circumbinary accretion. We also show that our parametrization of binary accretion increases the minimum mass ratio needed for spin alignment of supermassive black holes to q ˜ 0.4, with potentially important implications for the magnitude of velocity kicks acquired during black hole mergers.

  12. Slim accretion disks

    SciTech Connect

    Abramowicz, M.A.; Czerny, B.; Lasota, J.P.; Szuszkiewicz, E.

    1988-09-01

    A new branch of equilibrium solutions for stationary accretion disks around black holes is found. These solutions correspond to moderately super-Eddington accretion rates. The existence of the new branch is a consequence of an additional cooling due to general relativistic Roche lobe overflow and horizontal advection of heat. On an accretion rate versus surface density plane the new branch forms, together with the two standard branches (corresponding to the Shakura-Sunyaev accretion disk models) a characteristically S-shaped curve. This could imply a limit cycle-type behavior for black hole accretion flows with accretion rates close ot the Eddington one. 29 references.

  13. Artificial Disc Replacement

    MedlinePlus

    ... treat this condition, alternatives to disc replacement include fusion, nonoperative care or no treatment. Typically, surgery is ... operative treatment for disc pain has been spinal fusion. This is a surgical procedure in which disc ...

  14. The structure of protoplanetary discs around evolving young stars

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Johansen, Anders; Lambrechts, Michiel; Morbidelli, Alessandro

    2015-03-01

    The formation of planets with gaseous envelopes takes place in protoplanetary accretion discs on time scales of several million years. Small dust particles stick to each other to form pebbles, pebbles concentrate in the turbulent flow to form planetesimals and planetary embryos and grow to planets, which undergo substantial radial migration. All these processes are influenced by the underlying structure of the protoplanetary disc, specifically the profiles of temperature, gas scale height, and density. The commonly used disc structure of the minimum mass solar nebula (MMSN) is a simple power law in all these quantities. However, protoplanetary disc models with both viscous and stellar heating show several bumps and dips in temperature, scale height, and density caused by transitions in opacity, which are missing in the MMSN model. These play an important role in the formation of planets, since they can act as sweet spots for forming planetesimals via the streaming instability and affect the direction and magnitude of type-I migration. We present 2D simulations of accretion discs that feature radiative cooling and viscous and stellar heating, and they are linked to the observed evolutionary stages of protoplanetary discs and their host stars. These models allow us to identify preferred planetesimal and planet formation regions in the protoplanetary disc as a function of the disc's metallicity, accretion rate, and lifetime. We derive simple fitting formulae that feature all structural characteristics of protoplanetary discs during the evolution of several Myr. These fits are straightforward for applying to modelling any growth stage of planets where detailed knowledge of the underlying disc structure is required. Appendix A is available in electronic form at http://www.aanda.org

  15. 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

  16. Redundant disc

    NASA Technical Reports Server (NTRS)

    Barack, W. N.; Domas, P. A.; Beekman, S. W. (Inventor)

    1978-01-01

    A rotatable disc is described that consists of parallel plates tightly joined together for rotation about a hub. Each plate is provided with several angularly projecting spaced lands. The lands of each plate are interposed in alternating relationship between the lands of the next adjacent plate. In this manner, circumferential displacement of adjacent sectors in any one plate is prevented in the event that a crack develops. Each plate is redundantly sized so that, in event of structural failure of one plate, the remaining plates support a proportionate share of the load of the failed plate. The plates are prevented from separating laterally through the inclusion of generally radially extending splines which are inserted to interlock cooperating, circumferentially adjacent lands.

  17. Characteristics of transonic spherical symmetric accretion flow in Schwarzschild-de Sitter and Schwarzschild anti-de Sitter backgrounds, in pseudo-general relativistic paradigm

    NASA Astrophysics Data System (ADS)

    Ghosh, Shubhrangshu; Banik, Prabir

    2015-07-01

    In this paper, we present a complete work on steady state spherically symmetric Bondi type accretion flow in the presence of cosmological constant (Λ) in both Schwarzschild-de Sitter (SDS) and Schwarzschild anti-de Sitter (SADS) backgrounds considering an isolated supermassive black hole (SMBH), with the inclusion of a simple radiative transfer scheme, in the pseudo-general relativistic paradigm. We do an extensive analysis on the transonic behavior of the Bondi type accretion flow onto the cosmological BHs including a complete analysis of the global parameter space and the stability of flow, and do a complete study of the global family of solutions for a generic polytropic flow. Bondi type accretion flow in SADS background renders multiplicity in its transonic behavior with inner "saddle" type and outer "center" type sonic points, with the transonic solutions forming closed loops or contours. There is always a limiting value for ∣Λ∣ up to which we obtain valid stationary transonic solutions, which correspond to both SDS and SADS geometries; this limiting value moderately increases with the increasing radiative efficiency of the flow, especially correspond to Bondi type accretion flow in SADS background. Repulsive Λ suppresses the Bondi accretion rate by an order of magnitude for relativistic Bondi type accretion flow for a certain range in temperature, and with a marginal increase in the Bondi accretion rate if the corresponding accretion flow occurs in SADS background. However, for a strongly radiative Bondi type accretion flow with high mass accretion rate, the presence of cosmological constant do not much influence the corresponding Bondi accretion rate of the flow. Our analysis show that the relic cosmological constant has a substantial effect on Bondi type accretion flow onto isolated SMBHs and their transonic solutions beyond length-scale of kiloparsecs, especially if the Bondi type accretion occurs onto the host supergiant ellipticals or central

  18. Astro- and cosmochemical consequences of accretion bursts - I. The D/H ratio of water

    NASA Astrophysics Data System (ADS)

    Owen, James E.; Jacquet, Emmanuel

    2015-02-01

    The D/H ratio of water in protostellar systems is a result of both inheritance from the parent molecular cloud and isotopic exchange in the disc. A possibly widespread feature of disc evolution, ignored in previous studies, is accretion bursts (or FU Orionis outbursts), which may thermally process a large fraction of the water. One proposed underlying mechanism for FU Orionis outbursts relies on the presence of a magnetically dead zone. Here we examine the evolution of (D/H)water in 1D simulations of a disc's evolution that includes dead zones and infall from an envelope with given D/H ratio in the infalling water (˜10-3), and compare the results with similar calculations without dead zones. We find that the accretion bursts result in a significantly lower (D/H)water ratio and a more extended region (radius up to ˜1-3 au) where water is equilibrated with hydrogen gas (D/H = 2 × 10-5), when compared to burst-free models. Solar system constraints suggest that our solar nebula either experienced no accretion bursts and had a Schmidt number ≲ 0.2 or had a Schmidt number closer to `nominal' values (˜1) and experienced several accretion bursts. Finally, future observations of (D/H)water in protoplanetary discs will allow inferences about angular momentum properties of the disc during disc building and the role of accretion bursts.

  19. Sadness, Suicidality and Grades. NBER Working Paper No. 16239

    ERIC Educational Resources Information Center

    DeSimone, Jeffrey S.

    2010-01-01

    This study examines the past year relationship between GPA and experiencing a combination of two primary depression symptoms, feeling sad and losing interest in usual activities for at least two consecutive weeks, among high school students during 2001-2009. The GPA loss associated with sadness, as defined above, falls from slightly less than a…

  20. Childhood and Adult Sexual Abuse, Rumination on Sadness, and Dysphoria

    ERIC Educational Resources Information Center

    Conway, Michael; Mendelson, Morris; Giannopoulos, Constantina; Csank, Patricia A. R.; Holm, Susan L.

    2004-01-01

    Objective: The study addressed the hypothesis that adults reporting sexual abuse are more likely to exhibit a general tendency to ruminate on sadness. The relations between reported abuse, rumination on sadness, and dysphoria were also examined. Method: Undergraduate students (101 women and 100 men) reported on childhood and adult sexual abuse and…

  1. Use of the SADS Diagnostic Interview in Evaluating Legal Insanity.

    ERIC Educational Resources Information Center

    Rogers, Richard; And Others

    1984-01-01

    Examined clinical usefulness of the Schedule of Affective Disorders and Schizophrenia (SADS) diagnostic interview in evaluations of criminal responsibility. Findings, based on 78 evaluations from a forensic clinic, indicated that SADS successfully differentiated between sane and insane evaluatees. Differences were primarily in severity of symptoms…

  2. On the energy dissipation rate at the inner edge of circumbinary discs

    NASA Astrophysics Data System (ADS)

    Terquem, Caroline; Papaloizou, John C. B.

    2016-10-01

    We study, by means of numerical simulations and analysis, the details of the accretion process from a disc onto a binary system. We show that energy is dissipated at the edge of a circumbinary disc and this is associated with the tidal torque that maintains the cavity: angular momentum is transferred from the binary to the disc through the action of compressional shocks and viscous friction. These shocks can be viewed as being produced by fluid elements which drift into the cavity and, before being accreted, are accelerated onto trajectories that send them back to impact the disc. The rate of energy dissipation is approximately equal to the product of potential energy per unit mass at the disc's inner edge and the accretion rate, estimated from the disc parameters just beyond the cavity edge, that would occur without the binary. For very thin discs, the actual accretion rate onto the binary may be significantly less. We calculate the energy emitted by a circumbinary disc taking into account energy dissipation at the inner edge and also irradiation arising there from reprocessing of light from the stars. We find that, for tight PMS binaries, the SED is dominated by emission from the inner edge at wavelengths between 1-4 and 10 μm. This may apply to systems like CoRoT 223992193 and V1481 Ori.

  3. Can I solve my structure by SAD phasing? Anomalous signal in SAD phasing

    PubMed Central

    Terwilliger, Thomas C.; Bunkóczi, Gábor; Hung, Li-Wei; Zwart, Peter H.; Smith, Janet L.; Akey, David L.; Adams, Paul D.

    2016-01-01

    A key challenge in the SAD phasing method is solving a structure when the anomalous signal-to-noise ratio is low. A simple theoretical framework for describing measurements of anomalous differences and the resulting useful anomalous correlation and anomalous signal in a SAD experiment is presented. Here, the useful anomalous correlation is defined as the correlation of anomalous differences with ideal anomalous differences from the anomalous substructure. The useful anomalous correlation reflects the accuracy of the data and the absence of minor sites. The useful anomalous correlation also reflects the information available for estimating crystallographic phases once the substructure has been determined. In contrast, the anomalous signal (the peak height in a model-phased anomalous difference Fourier at the coordinates of atoms in the anomalous substructure) reflects the information available about each site in the substructure and is related to the ability to find the substructure. A theoretical analysis shows that the expected value of the anomalous signal is the product of the useful anomalous correlation, the square root of the ratio of the number of unique reflections in the data set to the number of sites in the substructure, and a function that decreases with increasing values of the atomic displacement factor for the atoms in the substructure. This means that the ability to find the substructure in a SAD experiment is increased by high data quality and by a high ratio of reflections to sites in the substructure, and is decreased by high atomic displacement factors for the substructure. PMID:26960122

  4. Appearance of Keplerian discs orbiting Kerr superspinars

    NASA Astrophysics Data System (ADS)

    Stuchlík, Zdeněk; Schee, Jan

    2010-11-01

    We study optical phenomena related to the appearance of Keplerian accretion discs orbiting Kerr superspinars predicted by string theory. The superspinar exterior is described by standard Kerr naked singularity geometry breaking the black hole limit on the internal angular momentum (spin). We construct local photon escape cones for a variety of orbiting sources that enable us to determine the superspinars silhouette in the case of distant observers. We show that the superspinar silhouette depends strongly on the assumed edge where the external Kerr spacetime is joined to the internal spacetime governed by string theory and significantly differs from the black hole silhouette. The appearance of the accretion disc is strongly dependent on the value of the superspinar spin in both their shape and frequency shift profile. Apparent extension of the disc grows significantly with the growing spin, while the frequency shift grows with the descending spin. This behaviour differs substantially from the appearance of discs orbiting black holes enabling thus, at least in principle, to distinguish clearly the Kerr superspinars and black holes. In vicinity of a Kerr superspinar the non-escaped photons have to be separated to those captured by the superspinar and those being trapped in its strong gravitational field leading to self-illumination of the disc that could even influence its structure and cause self-reflection effect of radiation of the disc. The amount of trapped photons grows with descending superspinar spin. We thus can expect significant self-illumination effects in the field of Kerr superspinars with near-extreme spin a ~ 1.

  5. Disc-planet interactions in subkeplerian discs

    NASA Astrophysics Data System (ADS)

    Paardekooper, S.-J.

    2009-11-01

    Context: One class of protoplanetary disc models, the X-wind model, predicts strongly subkeplerian orbital gas velocities, a configuration that can be sustained by magnetic tension. Aims: We investigate disc-planet interactions in these subkeplerian discs, focusing on orbital migration for low-mass planets and gap formation for high-mass planets. Methods: We use linear calculations and nonlinear hydrodynamical simulations to measure the torque and look at gap formation. In both cases, the subkeplerian nature of the disc is treated as a fixed external constraint. Results: We show that, depending on the degree to which the disc is subkeplerian, the torque on low-mass planets varies between the usual type I torque and the one-sided outer Lindblad torque, which is also negative but an order of magnitude stronger. In strongly subkeplerian discs, corotation effects can be ignored, making migration fast and inward. Gap formation near the planet's orbit is more difficult in such discs, since there are no resonances close to the planet accommodating angular momentum transport. The location of the gap is shifted inwards with respect to the planet, leaving the planet on the outside of a surface density depression. Conclusions: Depending on the degree to which a protoplanetary disc is subkeplerian, disc-planet interactions can be very different from the usual Keplerian picture, making these discs in general more hazardous for young planets.

  6. Relevance of jet emitting disc physics to microquasars: application to Cygnus X-1

    NASA Astrophysics Data System (ADS)

    Petrucci, P. O.; Ferreira, J.; Henri, G.; Malzac, J.; Foellmi, C.

    2010-11-01

    Context. Interpretation of the X-ray spectra of X-ray binaries during their hard states requires a hot, optically thin medium. There are several accretion disc models that account for this aspect. However, none is designed to simultaneously explain powerful jets detected during these states. Aims: A new quasi-Keplerian hot accretion disc solution, a jet emitting disc (JED hereafter), which is part of a global disc-jet MHD structure producing stationary super-alfvénic ejection, is investigated here. Its radiative and energetic properties are then compared to the observational constraints found in Cygnus X-1. Methods: We solve the disc energy equation by balancing the local heating term with advection and cooling by synchrotron, bremsstrahlung, and Comptonization processes. The heating term, disc density, accretion velocity, and magnetic field amplitude were taken from published self-similar models of accretion-ejection structures. Both optically thin and thick regimes are considered in a one-temperature, gas-supported disc. Results: Three branches of solutions are found to be possible at a given radius, but we only investigate the hot, optically thin and geometrically slim solutions. These solutions give simultaneously and consistently the radiative and energetics properties of the disc-jet system. They are able to reproduce the global accretion-ejection properties of Cygnus X-1 very well, namely its X-ray spectral emission, jet power, and jet velocity. About half of the released accretion power is used to produce two mildly relativistic (v/c≃ 0.5) jets, and for a luminosity of about 1% of the Eddington luminosity, the JED temperature and optical depth are close to what is observed in the hard state of Cygnus X-1. Conclusions: The accretion and ejection properties of JEDs agree with the observations of the prototypical black hole binary Cygnus X-1. The JED solutions are likely to be relevant to the whole class of microquasars.

  7. The pleasures of sad music: a systematic review.

    PubMed

    Sachs, Matthew E; Damasio, Antonio; Habibi, Assal

    2015-01-01

    Sadness is generally seen as a negative emotion, a response to distressing and adverse situations. In an aesthetic context, however, sadness is often associated with some degree of pleasure, as suggested by the ubiquity and popularity, throughout history, of music, plays, films and paintings with a sad content. Here, we focus on the fact that music regarded as sad is often experienced as pleasurable. Compared to other art forms, music has an exceptional ability to evoke a wide-range of feelings and is especially beguiling when it deals with grief and sorrow. Why is it, then, that while human survival depends on preventing painful experiences, mental pain often turns out to be explicitly sought through music? In this article we consider why and how sad music can become pleasurable. We offer a framework to account for how listening to sad music can lead to positive feelings, contending that this effect hinges on correcting an ongoing homeostatic imbalance. Sadness evoked by music is found pleasurable: (1) when it is perceived as non-threatening; (2) when it is aesthetically pleasing; and (3) when it produces psychological benefits such as mood regulation, and empathic feelings, caused, for example, by recollection of and reflection on past events. We also review neuroimaging studies related to music and emotion and focus on those that deal with sadness. Further exploration of the neural mechanisms through which stimuli that usually produce sadness can induce a positive affective state could help the development of effective therapies for disorders such as depression, in which the ability to experience pleasure is attenuated. PMID:26257625

  8. The pleasures of sad music: a systematic review.

    PubMed

    Sachs, Matthew E; Damasio, Antonio; Habibi, Assal

    2015-01-01

    Sadness is generally seen as a negative emotion, a response to distressing and adverse situations. In an aesthetic context, however, sadness is often associated with some degree of pleasure, as suggested by the ubiquity and popularity, throughout history, of music, plays, films and paintings with a sad content. Here, we focus on the fact that music regarded as sad is often experienced as pleasurable. Compared to other art forms, music has an exceptional ability to evoke a wide-range of feelings and is especially beguiling when it deals with grief and sorrow. Why is it, then, that while human survival depends on preventing painful experiences, mental pain often turns out to be explicitly sought through music? In this article we consider why and how sad music can become pleasurable. We offer a framework to account for how listening to sad music can lead to positive feelings, contending that this effect hinges on correcting an ongoing homeostatic imbalance. Sadness evoked by music is found pleasurable: (1) when it is perceived as non-threatening; (2) when it is aesthetically pleasing; and (3) when it produces psychological benefits such as mood regulation, and empathic feelings, caused, for example, by recollection of and reflection on past events. We also review neuroimaging studies related to music and emotion and focus on those that deal with sadness. Further exploration of the neural mechanisms through which stimuli that usually produce sadness can induce a positive affective state could help the development of effective therapies for disorders such as depression, in which the ability to experience pleasure is attenuated.

  9. The pleasures of sad music: a systematic review

    PubMed Central

    Sachs, Matthew E.; Damasio, Antonio; Habibi, Assal

    2015-01-01

    Sadness is generally seen as a negative emotion, a response to distressing and adverse situations. In an aesthetic context, however, sadness is often associated with some degree of pleasure, as suggested by the ubiquity and popularity, throughout history, of music, plays, films and paintings with a sad content. Here, we focus on the fact that music regarded as sad is often experienced as pleasurable. Compared to other art forms, music has an exceptional ability to evoke a wide-range of feelings and is especially beguiling when it deals with grief and sorrow. Why is it, then, that while human survival depends on preventing painful experiences, mental pain often turns out to be explicitly sought through music? In this article we consider why and how sad music can become pleasurable. We offer a framework to account for how listening to sad music can lead to positive feelings, contending that this effect hinges on correcting an ongoing homeostatic imbalance. Sadness evoked by music is found pleasurable: (1) when it is perceived as non-threatening; (2) when it is aesthetically pleasing; and (3) when it produces psychological benefits such as mood regulation, and empathic feelings, caused, for example, by recollection of and reflection on past events. We also review neuroimaging studies related to music and emotion and focus on those that deal with sadness. Further exploration of the neural mechanisms through which stimuli that usually produce sadness can induce a positive affective state could help the development of effective therapies for disorders such as depression, in which the ability to experience pleasure is attenuated. PMID:26257625

  10. Native sulfur/chlorine SAD phasing for serial femtosecond crystallography

    SciTech Connect

    Nakane, Takanori; Song, Changyong; Suzuki, Mamoru; Nango, Eriko; Kobayashi, Jun; Masuda, Tetsuya; Inoue, Shigeyuki; Mizohata, Eiichi; Nakatsu, Toru; Tanaka, Tomoyuki; Tanaka, Rie; Shimamura, Tatsuro; Tono, Kensuke; Joti, Yasumasa; Kameshima, Takashi; Hatsui, Takaki; Yabashi, Makina; Nureki, Osamu; Iwata, So; Sugahara, Michihiro

    2015-11-27

    Sulfur SAD phasing facilitates the structure determination of diverse native proteins using femtosecond X-rays from free-electron lasers via serial femtosecond crystallography. Serial femtosecond crystallography (SFX) allows structures to be determined with minimal radiation damage. However, phasing native crystals in SFX is not very common. Here, the structure determination of native lysozyme from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of sulfur and chlorine at a wavelength of 1.77 Å is successfully demonstrated. This sulfur SAD method can be applied to a wide range of proteins, which will improve the determination of native crystal structures.

  11. Can I solve my structure by SAD phasing? Anomalous signal in SAD phasing

    DOE PAGES

    Terwilliger, Thomas C.; Bunkóczi, Gábor; Hung, Li-Wei; Zwart, Peter H.; Smith, Janet L.; Akey, David L.; Adams, Paul D.

    2016-03-01

    A key challenge in the SAD phasing method is solving a structure when the anomalous signal-to-noise ratio is low. We present a simple theoretical framework for describing measurements of anomalous differences and the resulting useful anomalous correlation and anomalous signal in a SAD experiment. Here, the useful anomalous correlation is defined as the correlation of anomalous differences with ideal anomalous differences from the anomalous substructure. The useful anomalous correlation reflects the accuracy of the data and the absence of minor sites. The useful anomalous correlation also reflects the information available for estimating crystallographic phases once the substructure has been determined.more » In contrast, the anomalous signal (the peak height in a model-phased anomalous difference Fourier at the coordinates of atoms in the anomalous substructure) reflects the information available about each site in the substructure and is related to the ability to find the substructure. A theoretical analysis shows that the expected value of the anomalous signal is the product of the useful anomalous correlation, the square root of the ratio of the number of unique reflections in the data set to the number of sites in the substructure, and a function that decreases with increasing values of the atomic displacement factor for the atoms in the substructure. In conclusion, this means that the ability to find the substructure in a SAD experiment is increased by high data quality and by a high ratio of reflections to sites in the substructure, and is decreased by high atomic displacement factors for the substructure.« less

  12. Black hole accretion.

    PubMed

    Narayan, Ramesh; Quataert, Eliot

    2005-01-01

    Black holes are most often detected by the radiation produced when they gravitationally pull in surrounding gas, in a process called accretion. The efficiency with which the hot gas radiates its thermal energy strongly influences the geometry and dynamics of the accretion flow. Both radiatively efficient thin disks and radiatively inefficient thick disks are observed. When the accreting gas gets close to the central black hole, the radiation it produces becomes sensitive to the spin of the hole and the presence of an event horizon. Analysis of the luminosities and spectra of accreting black holes has yielded tantalizing evidence for both rotating holes and event horizons. Numerical simulations imply that the relativistic jets often seen from accreting black holes may be powered in part by the spin of the hole. PMID:15637269

  13. Effect of regulating anger and sadness on decision-making.

    PubMed

    Szasz, Paul Lucian; Hofmann, Stefan G; Heilman, Renata M; Curtiss, Joshua

    2016-11-01

    The aim of the current study was to investigate the effects of reappraisal, acceptance, and rumination for regulating anger and sadness on decision-making. Participants (N = 165) were asked to recall two autobiographical events in which they felt intense anger and sadness, respectively. Participants were then instructed to reappraise, accept, ruminate, or not use any strategies to regulate their feelings of anger and sadness. Following this manipulation, risk aversion, and decision-making strategies were measured using a computer-based measure of risk-taking and a simulated real-life decision-making task. Participants who were instructed to reappraise their emotions showed the least anger and sadness, the most adaptive decision-making strategies, but the least risk aversion as compared to the participants in the other conditions. These findings suggest that emotion regulation strategies of negative affective states have an immediate effect on decision-making and risk-taking behaviors. PMID:27438753

  14. Effect of regulating anger and sadness on decision-making.

    PubMed

    Szasz, Paul Lucian; Hofmann, Stefan G; Heilman, Renata M; Curtiss, Joshua

    2016-11-01

    The aim of the current study was to investigate the effects of reappraisal, acceptance, and rumination for regulating anger and sadness on decision-making. Participants (N = 165) were asked to recall two autobiographical events in which they felt intense anger and sadness, respectively. Participants were then instructed to reappraise, accept, ruminate, or not use any strategies to regulate their feelings of anger and sadness. Following this manipulation, risk aversion, and decision-making strategies were measured using a computer-based measure of risk-taking and a simulated real-life decision-making task. Participants who were instructed to reappraise their emotions showed the least anger and sadness, the most adaptive decision-making strategies, but the least risk aversion as compared to the participants in the other conditions. These findings suggest that emotion regulation strategies of negative affective states have an immediate effect on decision-making and risk-taking behaviors.

  15. Beat the Winter Blues: Shedding Light on Seasonal Sadness

    MedlinePlus

    ... exit disclaimer . Subscribe Beat the Winter Blues Shedding Light on Seasonal Sadness As the days get shorter, ... clock” responds to cues in your surroundings, especially light and darkness. During the day, your brain sends ...

  16. Turbine disc sealing assembly

    DOEpatents

    Diakunchak, Ihor S.

    2013-03-05

    A disc seal assembly for use in a turbine engine. The disc seal assembly includes a plurality of outwardly extending sealing flange members that define a plurality of fluid pockets. The sealing flange members define a labyrinth flow path therebetween to limit leakage between a hot gas path and a disc cavity in the turbine engine.

  17. Native sulfur/chlorine SAD phasing for serial femtosecond crystallography.

    PubMed

    Nakane, Takanori; Song, Changyong; Suzuki, Mamoru; Nango, Eriko; Kobayashi, Jun; Masuda, Tetsuya; Inoue, Shigeyuki; Mizohata, Eiichi; Nakatsu, Toru; Tanaka, Tomoyuki; Tanaka, Rie; Shimamura, Tatsuro; Tono, Kensuke; Joti, Yasumasa; Kameshima, Takashi; Hatsui, Takaki; Yabashi, Makina; Nureki, Osamu; Iwata, So; Sugahara, Michihiro

    2015-12-01

    Serial femtosecond crystallography (SFX) allows structures to be determined with minimal radiation damage. However, phasing native crystals in SFX is not very common. Here, the structure determination of native lysozyme from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of sulfur and chlorine at a wavelength of 1.77 Å is successfully demonstrated. This sulfur SAD method can be applied to a wide range of proteins, which will improve the determination of native crystal structures.

  18. Native sulfur/chlorine SAD phasing for serial femtosecond crystallography

    PubMed Central

    Nakane, Takanori; Song, Changyong; Suzuki, Mamoru; Nango, Eriko; Kobayashi, Jun; Masuda, Tetsuya; Inoue, Shigeyuki; Mizohata, Eiichi; Nakatsu, Toru; Tanaka, Tomoyuki; Tanaka, Rie; Shimamura, Tatsuro; Tono, Kensuke; Joti, Yasumasa; Kameshima, Takashi; Hatsui, Takaki; Yabashi, Makina; Nureki, Osamu; Iwata, So; Sugahara, Michihiro

    2015-01-01

    Serial femtosecond crystallography (SFX) allows structures to be determined with minimal radiation damage. However, phasing native crystals in SFX is not very common. Here, the structure determination of native lysozyme from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of sulfur and chlorine at a wavelength of 1.77 Å is successfully demonstrated. This sulfur SAD method can be applied to a wide range of proteins, which will improve the determination of native crystal structures. PMID:26627659

  19. Standardized mood induction with happy and sad facial expressions.

    PubMed

    Schneider, F; Gur, R C; Gur, R E; Muenz, L R

    1994-01-01

    The feasibility of applying ecologically valid and socially relevant emotional stimuli in a standardized fashion to obtain reliable mood changes in healthy subjects was examined. The stimuli consisted of happy and sad facial expressions varying in intensity. Two mood-induction procedures (happy and sad, each consisting of 40 slides) were administered to 24 young healthy subjects, who were instructed to look at each slide (self-paced) and try to feel the happy or sad mood expressed by the person in the picture. On an emotional self-rating scale, subjects rated themselves as relatively happier during the happy mood-induction condition and as relatively sadder during the sad mood-induction condition. Conversely, they reported that they were less happy during the sad mood-induction condition and less sad during the happy mood-induction condition. The effects were generalized to positive and negative affect as measured by the Positive and Negative Affect Scale. The intraindividual variability in the effect was very small. In a retest study after 1 month, the mood-induction effects showed good stability over time. The results encourage the use of this mood-induction procedure as a neurobehavioral probe in physiologic neuroimaging studies for investigating the neural substrates of emotional experience.

  20. Density, Velocity and Ionization Structure in Accretion-Disc Winds

    NASA Technical Reports Server (NTRS)

    Sonneborn, George (Technical Monitor); Long, Knox

    2004-01-01

    This was a project to exploit the unique capabilities of FUSE to monitor variations in the wind- formed spectral lines of the luminous, low-inclination, cataclysmic variables(CV) -- RW Sex. (The original proposal contained two additional objects but these were not approved.) These observations were intended to allow us to determine the relative roles of density and ionization state changes in the outflow and to search for spectroscopic signatures of stochastic small-scale structure and shocked gas. By monitoring the temporal behavior of blue-ward extended absorption lines with a wide range of ionization potentials and excitation energies, we proposed to track the changing physical conditions in the outflow. We planned to use a new Monte Carlo code to calculate the ionization structure of and radiative transfer through the CV wind. The analysis therefore was intended to establish the wind geometry, kinematics and ionization state, both in a time-averaged sense and as a function of time.

  1. Rotating Bondi Accretion Flow

    NASA Astrophysics Data System (ADS)

    Park, Myeong-Gu; Han, Du-Hwan

    2016-06-01

    The characteristics of accretion flow onto a black hole are determined by the physical condition of gas at large radius. When the gas has no angular momentum and is polytropic, the accretion flow becomes the classic Bondi flow. The mass accretion rate in such case is an eigenvalue and uniquely determined by the density and the temperature of the surrounding gas for a given black hole mass. When the gas has angular momentum above some critical value, the angular momentum of the gas should be removed by viscosity to reach the black hole horizon. We study, within the slim disk approximation, rotating polytropic accretion flow with alpha viscosity as an an extension of the Bondi flow. The characteristics of the accretion flow are now determined by the temperature, density, and angular momentum of the gas at the outer boundary. We explore the effects of the viscosity parameter and the outer boundary radius on the physical characteristic of the flow, especially on the mass accretion rate, and compare the result with previous works of Park (2009) and Narayan & Fabian (2011).

  2. In-House Zinc SAD Phasing at Cu Kα Edge

    PubMed Central

    Kim, Min-Kyu; Lee, Sangmin; An, Young Jun; Jeong, Chang-Sook; Ji, Chang-Jun; Lee, Jin-Won; Cha, Sun-Shin

    2013-01-01

    De novo zinc single-wavelength anomalous dispersion (Zn-SAD) phasing has been demonstrated with the 1.9 Å resolution data of glucose isomerase and 2.6 Å resolution data of Staphylococcus aureus Fur (SaFur) collected using in-house Cu Kα X-ray source. The successful in-house Zn-SAD phasing of glucose isomerase, based on the anomalous signals of both zinc ions introduced to crystals by soaking and native sulfur atoms, drove us to determine the structure of SaFur, a zinc-containing transcription factor, by Zn-SAD phasing using in-house X-ray source. The abundance of zinc-containing proteins in nature, the easy zinc derivatization of the protein surface, no need of synchrotron access, and the successful experimental phasing with the modest 2.6 Å resolution SAD data indicate that in-house Zn-SAD phasing can be widely applicable to structure determination. PMID:23686432

  3. Inner disc obscuration in GRS 1915+105 based on relativistic slim disc model

    NASA Astrophysics Data System (ADS)

    Vierdayanti, K.; Sadowski, A.; Mineshige, S.; Bursa, M.

    2013-11-01

    We study the observational signatures of the relativistic slim disc of 10 M⊙ black hole, in a wide range of mass accretion rate, dot{m}, dimensionless spin parameter, a*, and viewing angle, i. In general, the innermost temperature, Tin, increases with the increase of i for a fixed value of dot{m} and a*, due to the Doppler effect. However, for i > 50° and dot{m}>dot{m}_turn, Tin starts to decrease with the increase of dot{m}. This is a result of self-obscuration - the radiation from the innermost hot part of the disc is blocked by the surrounding cooler part. The value of dot{m}_turn and the corresponding luminosities depend on a* and i. Such obscuration effects cause an interesting behaviour on the disc luminosity (Ldisc)-Tin plane for high inclinations. In addition to the standard disc branch which appears below dot{m}_turn and which obeys L_disc ∝ T_in4 relation, another branch above dot{m}_turn, which is nearly horizontal, may be observed at luminosities close to the Eddington luminosity. We show that these features are likely observed in a Galactic X-ray source, GRS 1915+105. We support a high spin parameter (a* > 0.9) for GRS 1915+105 since otherwise the high value of Tin and small size of the emitting region (rin < 1rS) cannot be explained.

  4. Implications of pebble accretion on the composition of hot and cold Jupiters

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Johansen, Anders; Madhusudhan, Nikku

    2016-10-01

    The formation of the planetary cores of gas giants via the accretion of planetesimals takes very long and is not compatible with the lifetime of protoplanetary discs (Levison et al. 2010). This time-scale problem can be solved through the accretion of pebbles onto a planetary seed. Contrary to planetesimals, pebbles feel the headwind from the gas which robs them of angular momentum allowing an efficient growth from the entire Hill sphere, which reduces the growth time-scale by several orders of magnitude (Lambrechts & Johansen, 2012; 2014). However, pebble accretion self-terminates when the planets start to open a partial gap in the disc, which accelerates the gas outside of the planets orbit to super-Keplerian speeds and thus stops the flow of pebbles onto the planetary core (Lambrechts et al. 2014). Typically this mass is of the order of 10-20 Earth masses, depending on the local disc properties. The planet can then start to accrete a gaseous envelope without a pollution of pebbles. During its growth, the planet migrates through the disc, which evolves in time (Bitsch et al. 2015a,b).Different volatile species like CO2 or H2O have different condensation temperatures and are thus present in either solid or gaseous form at different locations in the disc. A pebble accreting planet can thus only accrete volatiles that are in solid form, while a gas accreting planet will only accrete volatiles which are in gaseous form. Therefore the final chemical composition of the planetary atmosphere of a giant planet is strongly influenced by the formation location of the initial planetary seed and its subsequent migration path through the disc. Additionally, the envelope can be enriched through the erosion of the planetary core.I will discuss the implications of the formation of planets via pebble accretion and their subsequent migration through the disc on the composition of gas giants. In particular I will focus on the carbon to oxygen ratio of hot Jupiters around other stars

  5. Computer disc revolution.

    PubMed

    Nunnally, R H

    1994-05-01

    CD-ROM Computer Discs with read only memory are etched in polycarbonate discs that permit storage of up to 400,000 pages on a single disc. Use of this technology supplemented by access to the National Library of Medicine or a large information service brings the medical library to the rural physician's office. This allows pertinent journal information to be applied to day-to-day office practice. PMID:8034564

  6. Do Poor Readers Feel Angry, Sad, and Unpopular?

    PubMed Central

    Morgan, Paul L.; Farkas, George; Wu, Qiong

    2015-01-01

    We investigated whether being poorly skilled in reading contributes to children’s self-reported feelings of anger, distractibility, anxiety, sadness, loneliness, and social isolation. Data were analyzed from a longitudinal sub-sample of children (N=2,751) participating in the Early Childhood Longitudinal Study—Kindergarten Cohort. Multi-level logistic regression analyses indicated that poor readers in 3rd grade were more likely to consider themselves as angry, distractible, sad, lonely, and unpopular in 5th grade than those who had not been poor readers in 3rd grade. About 20% of 3rd grade poor readers reported feeling angry and unpopular in 5th grade. Being poorly skilled in mathematics increased children’s risk of feeling sad or lonely, but not of feeling angry, distractible, or unpopular. The results provide additional empirical evidence that reading failure contributes to generalized socio-emotional maladjustment in young children. PMID:26180489

  7. On the formation of a quasi-stationary twisted disc after a tidal disruption event

    NASA Astrophysics Data System (ADS)

    Xiang-Gruess, M.; Ivanov, P. B.; Papaloizou, J. C. B.

    2016-08-01

    We investigate misaligned accretion discs formed after tidal disruption events that occur when a star encounters a supermassive black hole. We employ the linear theory of warped accretion discs to find the shape of a disc for which the stream arising from the disrupted star provides a source of angular momentum that is misaligned with that of the black hole. For quasi-steady configurations we find that when the warp diffusion or propagation time is large compared to the local mass accretion time and/or the natural disc alignment radius is small, misalignment is favoured. These results have been verified using SPH simulations. We also simulated 1D model discs including gas and radiation pressure. As accretion rates initially exceed the Eddington limit the disc is initially advection dominated. Assuming the α model for the disc, where it can be thermally unstable it subsequently undergoes cyclic transitions between high and low states. During these transitions the aspect ratio varies from ˜1 to ˜10-3 which is reflected in changes in the degree of disc misalignment at the stream impact location. For maximal black hole rotation and sufficiently large values of viscosity parameter α > ˜0.01 - 0.1 the ratio of the disc inclination to that of the initial stellar orbit is estimated to be 0.1 - 0.2 in the advection dominated state, while reaching of order unity in the low state. Misalignment descreases with decrease of α, but increases as the black hole rotation parameter decreases. Thus, it is always significant when the latter is small.

  8. Outwards migration for planets in stellar irradiated 3D discs

    NASA Astrophysics Data System (ADS)

    Lega, E.; Morbidelli, A.; Bitsch, B.; Crida, A.; Szulágyi, J.

    2015-09-01

    For the very first time we present 3D simulations of planets embedded in stellar irradiated discs. It is well known that thermal effects could reverse the direction of planetary migration from inwards to outwards, potentially saving planets in the inner, optically thick parts of the protoplanetary disc. When considering stellar irradiation in addition to viscous friction as a source of heating, the outer disc changes from a shadowed to a flared structure. Using a suited analytical formula it has been shown that in the flared part of the disc the migration is inwards; planets can migrate outwards only in shadowed regions of the disc, because the radial gradient of entropy is stronger there. In order to confirm this result numerically, we have computed the total torque acting on planets held on fixed orbits embedded in stellar irradiated 3D discs using the hydrodynamical code FARGOCA. We find qualitatively good agreement between the total torque obtained with numerical simulations and the one predicted by the analytical formula. For large masses (>20 M⊕) we find quantitative agreement, and we obtain outwards migration regions for planets up to 60 M⊕ in the early stages of accretional discs. We find nevertheless that the agreement with the analytic formula is quite fortuitous because the formula underestimates the size of the horseshoe region; this error is compensated by imperfect estimates of other terms, most likely the cooling rate and the saturation.

  9. Evolutionary constraints on the planetary hypothesis for transition discs

    NASA Astrophysics Data System (ADS)

    Clarke, C. J.; Owen, J. E.

    2013-06-01

    We assume a scenario in which transition discs (i.e. discs around young stars that have signatures of cool dust but lack significant near-infrared emission from warm dust) are associated with the presence of planets (or brown dwarfs). These are assumed to filter the dust content of any gas flow within the planetary orbit and produce an inner `opacity hole'. In order to match the properties of transition discs with the largest (˜50 au scale) holes, we place such `planets' at large radii in massive discs and then follow the evolution of the tidally coupled disc-planet system, comparing the system's evolution in the plane of mm flux against hole radius with the properties of observed transition discs. We find that, on account of the high disc masses in these systems, all but the most massive `planets' (100 Jupiter masses) are conveyed to small radii by Type II migration without significant fading at millimetre wavelengths. Such behaviour would contradict the observed lack of mm bright transition discs with small (<10 au) holes. On the other hand, imaging surveys clearly rule out the presence of such massive companions in transition discs. We conclude that this is a serious problem for models that seek to explain transition discs in terms of planetary companions unless some mechanism can be found to halt inward migration and/or suppress mm flux production. We suggest that the dynamical effects of substantial accretion on to the planet/through the gap may offer the best prospect for halting such migration and that further long-term simulations are required to clarify this issue.

  10. Star Formation and Gas Accretion in Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Yim, Kijeong; van der Hulst, J. M.

    2016-08-01

    In order to quantify the relationship between gas accretion and star formation, we analyse a sample of 29 nearby galaxies from the WHISP survey which contains galaxies with and without evidence for recent gas accretion. We compare combined radial profiles of FUV (GALEX) and IR 24 μm (Spitzer) characterizing distributions of recent star formation with radial profiles of CO (IRAM, BIMA, or CARMA) and H I (WSRT) tracing molecular and atomic gas contents to examine star formation efficiencies in symmetric (quiescent), asymmetric (accreting), and interacting (tidally disturbed) galaxies. In addition, we investigate the relationship between star formation rate and H I in the outer discs for the three groups of galaxies. We confirm the general relationship between gas surface density and star formation surface density, but do not find a significant difference between the three groups of galaxies.

  11. Geometry of X-ray sources in accreting black-hole binaries

    NASA Astrophysics Data System (ADS)

    Zdziarski, Andrzej

    2016-07-01

    The structure of the X-ray sources in the hard spectral state of accreting black-hole binaries has been a subject of intense debate. The paradigm dominant for many years postulated that the accretion disc in the hard state is truncated at some radius >> the innermost stable orbit (ISCO) whereas the disc reaches the ISCO in the soft state. This paradigm explains a large body of observed phenomena, including the spectral and variability differences between the states and outbursts of transient sources, proceeding from quiescence (where no disc is present) through the hard state to the peak flux in the soft state. On the other hand, there have been numerous claims in recent years that the disc extends to the ISCO in the hard state. Also, the primary X-ray source has been postulated to consist of a compact source on-axis of the rotating black hole (a lamppost). Those claims are based on observations of broad Fe K lines and of soft X-ray components interpreted as blackbody-emitting accretion discs. I will discuss arguments for and against the disc truncation and the lamppost geometry based on current spectral and timing results.

  12. Efficiency of super-Eddington magnetically-arrested accretion

    NASA Astrophysics Data System (ADS)

    McKinney, Jonathan C.; Dai, Lixin; Avara, Mark J.

    2015-11-01

    The radiative efficiency of super-Eddington accreting black holes (BHs) is explored for magnetically-arrested discs, where magnetic flux builds-up to saturation near the BH. Our three-dimensional general relativistic radiation magnetohydrodynamic (GRRMHD) simulation of a spinning BH (spin a/M = 0.8) accreting at ˜50 times Eddington shows a total efficiency ˜50 per cent when time-averaged and total efficiency ≳ 100 per cent in moments. Magnetic compression by the magnetic flux near the rotating BH leads to a thin disc, whose radiation escapes via advection by a magnetized wind and via transport through a low-density channel created by a Blandford-Znajek (BZ) jet. The BZ efficiency is sub-optimal due to inertial loading of field lines by optically thick radiation, leading to BZ efficiency ˜40 per cent on the horizon and BZ efficiency ˜5 per cent by r ˜ 400rg (gravitational radii) via absorption by the wind. Importantly, radiation escapes at r ˜ 400rg with efficiency η ≈ 15 per cent (luminosity L ˜ 50LEdd), similar to η ≈ 12 per cent for a Novikov-Thorne thin disc and beyond η ≲ 1 per cent seen in prior GRRMHD simulations or slim disc theory. Our simulations show how BH spin, magnetic field, and jet mass-loading affect these radiative and jet efficiencies.

  13. Subhalo Accretion through Filaments

    NASA Astrophysics Data System (ADS)

    González, Roberto E.; Padilla, Nelson D.

    2016-09-01

    We track subhalo orbits of galaxy- and group-sized halos in cosmological simulations. We identify filamentary structures around halos and use these to define a sample of subhalos accreted from filaments, as well as a control sample of subhalos accreted from other directions. We use these samples to study differences in satellite orbits produced by filamentary accretion. Our results depend on host halo mass. We find that for low masses, subhalos accreted from filaments show ∼10% shorter lifetimes compared to the control sample, show a tendency toward more radial orbits, reach halo central regions earlier, and are more likely to merge with the host. For higher-mass halos this lifetime difference dissipates and even reverses for cluster-sized halos. This behavior appears to be connected to the fact that more massive hosts are connected to stronger filaments with higher velocity coherence and density, with slightly more radial subhalo orbits. Because subhalos tend to follow the coherent flow of the filament, it is possible that such thick filaments are enough to shield the subhalo from the effect of dynamical friction at least during their first infall. We also identify subhalo pairs/clumps that merge with one another after accretion. They survive as a clump for only a very short time, which is even shorter for higher subhalo masses, suggesting that the Magellanic Clouds and other Local group satellite associations may have entered the Milky Way virial radius very recently and probably are in their first infall.

  14. Are quasars accreting at super-Eddington rates?

    NASA Astrophysics Data System (ADS)

    Collin, S.; Boisson, C.; Mouchet, M.; Dumont, A.-M.; Coupé, S.; Porquet, D.; Rokaki, E.

    2002-06-01

    In a previous paper, Collin & Huré (\\cite{Collin2001e}), using a sample of Active Galactic Nuclei (AGN) where the mass has been determined by reverberation studies (the Kaspi et al. \\cite{Kaspi} sample), have shown that if the optical luminosity is emitted by a steady accretion disc, it implies that about half of the objects of the sample are accreting close to the Eddington rate or at super-Eddington rates. We discuss here this problem in more detail, evaluating different uncertainties, and we conclude that this result is unavoidable, unless the masses are strongly underestimated by reverberation studies. This can occur if the broad line region is a flat thin rotating structure with the same axis as the accretion disc, close to the line of sight. However the masses deduced from reverberation mapping in AGN follow the same correlation between the black hole mass and the bulge mass as normal galaxies (Laor \\cite{Laor2001}), suggesting that they are correct within a factor of a few. There are then three issues to the problem: 1. accretion proceeds at Eddington or super-Eddington rates in these objects through slim or thick discs; 2. the optical luminosity is not produced directly by the gravitational release of energy, but by another mechanism, so super-Eddington rates are not required; 3. accretion discs are completely ``non standard". Presently neither the predictions of models nor the observed spectral distributions are sufficient to help choose between these solutions. In particular, even for the super-Eddington model, the observed optical to bolometric luminosity ratio would be of the order of the observed one. In the super-Eddington solution, there is a strong anti-correlation between the observed velocity widths of the lines and the computed Eddington ratios (i.e. the accretion rate to the Eddington rate ratios), the largest ratios corresponding to the narrowest lines, actually to ``Narrow Line Seyfert 1" nuclei. For the considered sample, the Eddington

  15. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion.

    PubMed

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-04-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts. PMID:26601169

  16. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion.

    PubMed

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-04-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

  17. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

    PubMed Central

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-01-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag–assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars’s size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts. PMID:26601169

  18. Estimating the fossil disc mass during supermassive black hole mergers: the importance of torque implementation

    NASA Astrophysics Data System (ADS)

    Tazzari, M.; Lodato, G.

    2015-05-01

    In this paper, we revisit the issue of estimating the `fossil' disc mass in the circumprimary disc, during the merger of a supermassive black hole binary. As the binary orbital decay speeds up due to the emission of gravitational waves, the gas in the circumprimary disc might be forced to accrete rapidly and could in principle provide a significant electromagnetic counterpart to the gravitational wave emission. Since the luminosity of such flare is proportional to the gaseous mass in the circumprimary disc, estimating such mass accurately is important. Previous investigations of this issue have produced contradictory results, with some authors estimating super-Eddington flares and large disc mass, while others suggesting that the `fossil' disc mass is very low, even less than a Jupiter mass. Here, we perform simple 1D calculations to show that such very low estimates of the disc mass are an artefact of the specific implementation of the tidal torque in 1D models. In particular, for moderate mass ratios of the binary, the usual formula for the torque used in 1D models significantly overestimates the width of the gap induced by the secondary and this artificially leads to a very small leftover circumprimary disc. Using a modified torque, calibrated to reproduce the correct gap width as estimated by 3D models, leads to fossil disc masses of the order of one solar mass. The rapid accretion of the whole circumprimary disc would produce peak luminosities of the order of 1-20 times the Eddington luminosity. Even if a significant fraction of the gas escapes accretion by flowing out the secondary orbit during the merger (an effect not included in our calculations), we would still predict close to Eddington luminosities that might be easily detected.

  19. Efficiency of thin magnetically arrested discs around black holes

    NASA Astrophysics Data System (ADS)

    Avara, Mark J.; McKinney, Jonathan C.; Reynolds, Christopher S.

    2016-10-01

    The radiative and jet efficiencies of thin magnetized accretion discs around black holes (BHs) are affected by BH spin and the presence of a magnetic field that, when strong, could lead to large deviations from Novikov-Thorne (NT) thin disc theory. To seek the maximum deviations, we perform general relativistic magnetohydrodynamic simulations of radiatively efficient thin (half-height H to radius R of H/R ≈ 0.10) discs around moderately rotating BHs with a/M = 0.5. First, our simulations, each evolved for more than 70 000 rg/c (gravitational radius rg and speed of light c), show that large-scale magnetic field readily accretes inward even through our thin disc and builds-up to the magnetically arrested disc (MAD) state. Secondly, our simulations of thin MADs show the disc achieves a radiative efficiency of ηr ≈ 15 per cent (after estimating photon capture), which is about twice the NT value of ηr ˜ 8 per cent for a/M = 0.5 and gives the same luminosity as an NT disc with a/M ≈ 0.9. Compared to prior simulations with ≲10 per cent deviations, our result of an ≈80 per cent deviation sets a new benchmark. Building on prior work, we are now able to complete an important scaling law which suggests that observed jet quenching in the high-soft state in BH X-ray binaries is consistent with an ever-present MAD state with a weak yet sustained jet.

  20. Quasar discs. II - A composite model for the broad-line region

    NASA Astrophysics Data System (ADS)

    Netzer, Hagai

    1987-03-01

    The possibility of geometrically thin accretion discs in active galactic nuclei (AGNs) was discussed in Paper I of this series (H. Netzer, 1985). The apparent luminosity of such discs depends on the viewing angle and this may be the reason for the observed correlation of continuum brightness and line equivalent width. This idea is taken one step further in the present work and the emission line spectrum of a gas exposed to the anisotropic ionizing radiation of a disc is investigated. One example which is studied in detail is that of a disc UV continuum combined with an isotropic X-ray source. Analysis of the L-M relationship in AGNs, within the framework of the new model, shows that these objects have smaller central masses and higher accretion efficiencies compared with previous estimates. There are important consequences for the two-phase model and cloud formation, and specific predictions of the observed LUV/LX, which is angle dependent.

  1. Quiet Times: The Place for Sadness in Growing Up.

    ERIC Educational Resources Information Center

    Peter, Val J.

    1999-01-01

    Compares clinical depression with reactive depression, a normal part of childhood development. Looks at quiet times children may experience, and provides examples of how normal childhood sadness can turn into depression. Suggests coping mechanisms and support structures that can prevent this cycle from occurring. (Author/JDM)

  2. Simultaneous anammox and denitrification (SAD) process in sequencing batch reactors.

    PubMed

    Takekawa, Masashi; Park, Giri; Soda, Satoshi; Ike, Michihiko

    2014-12-01

    This study investigated nitrogen removal by the simultaneous anaerobic ammonium oxidation (anammox) and heterotrophic denitrification (SAD) process in a sequencing batch reactor (SBR) inoculated with suspended activated sludge and immobilized anammox sludge at various total organic carbon/nitrate (C/N) ratios. Synthetic wastewater containing nitrate 100mg-NL(-1), ammonium 70mg-NL(-1), and acetate 50-250mg-CL(-1) was fed to the SBR. Nitrite reduced from nitrate by heterotrophic denitrification was accumulated and removed with ammonium in each cycle operation of the SBR. The SAD process removed nitrate and ammonium effectively (T-N removal, 58-94%) by the high anammox contribution (ca. 80-100%) under low C/N ratios (0.5-1.0). At high C/N ratios of 1.2-2.5, the SAD process maintained T-N removal 67-79% with predominance of heterotrophic denitrification instead of anammox reaction. Results demonstrated that the SAD process performs high nitrogen removal effectively from wastewater with widely different C/N ratios.

  3. From Unresolved Anger to Sadness: Identifying Physiological Correlates

    ERIC Educational Resources Information Center

    Rochman, Daniel; Diamond, Gary M.

    2008-01-01

    This study was designed to identify physiological correlates of unresolved anger and sadness, and the shift between these emotions, in a context similar to that of emotion-focused, experiential psychotherapy. Twenty-seven university students reporting unresolved anger toward an attachment figure were induced to experience and express unresolved…

  4. Laughter exaggerates happy and sad faces depending on visual context.

    PubMed

    Sherman, Aleksandra; Sweeny, Timothy D; Grabowecky, Marcia; Suzuki, Satoru

    2012-04-01

    Laughter is an auditory stimulus that powerfully conveys positive emotion. We investigated how laughter influenced the visual perception of facial expressions. We presented a sound clip of laughter simultaneously with a happy, a neutral, or a sad schematic face. The emotional face was briefly presented either alone or among a crowd of neutral faces. We used a matching method to determine how laughter influenced the perceived intensity of the happy, neutral, and sad expressions. For a single face, laughter increased the perceived intensity of a happy expression. Surprisingly, for a crowd of faces, laughter produced an opposite effect, increasing the perceived intensity of a sad expression in a crowd. A follow-up experiment revealed that this contrast effect may have occurred because laughter made the neutral distractor faces appear slightly happy, thereby making the deviant sad expression stand out in contrast. A control experiment ruled out semantic mediation of the laughter effects. Our demonstration of the strong context dependence of laughter effects on facial expression perception encourages a reexamination of the previously demonstrated effects of prosody, speech content, and mood on face perception, as they may be similarly context dependent.

  5. Do Poor Readers Feel Angry, Sad, and Unpopular?

    ERIC Educational Resources Information Center

    Morgan, Paul L.; Farkas, George; Wu, Qiong

    2012-01-01

    We investigated whether being poorly skilled in reading contributes to children's reported feelings of anger, distractibility, anxiety, sadness, loneliness, and social isolation. Data were analyzed from a longitudinal subsample of children (N = 3,308) participating in the Early Childhood Longitudinal Study-Kindergarten Cohort. Multilevel logistic…

  6. A Season of Sadness--"Responding to Tragedy in School"

    ERIC Educational Resources Information Center

    Havlland, Joseph E.

    2008-01-01

    In January, four juniors died in an automobile accident; in February a member of the previous year's graduating class committed suicide; in March a member of the faculty died suddenly; and a crazed gunman killed three current and one former student. Spring 1999 was a season of sadness. Several Penncrest faculty meetings were devoted to reviewing…

  7. Being Moved by Unfamiliar Sad Music Is Associated with High Empathy

    PubMed Central

    Eerola, Tuomas; Vuoskoski, Jonna K.; Kautiainen, Hannu

    2016-01-01

    The paradox of enjoying listening to music that evokes sadness is yet to be fully understood. Unlike prior studies that have explored potential explanations related to lyrics, memories, and mood regulation, we investigated the types of emotions induced by unfamiliar, instrumental sad music, and whether these responses are consistently associated with certain individual difference variables. One hundred and two participants were drawn from a representative sample to minimize self-selection bias. The results suggest that the emotional responses induced by unfamiliar sad music could be characterized in terms of three underlying factors: Relaxing sadness, Moving sadness, and Nervous sadness. Relaxing sadness was characterized by felt and perceived peacefulness and positive valence. Moving sadness captured an intense experience that involved feelings of sadness and being moved. Nervous sadness was associated with felt anxiety, perceived scariness and negative valence. These interpretations were supported by indirect measures of felt emotion. Experiences of Moving sadness were strongly associated with high trait empathy and emotional contagion, but not with other previously suggested traits such as absorption or nostalgia-proneness. Relaxing sadness and Nervous sadness were not significantly predicted by any of the individual difference variables. The findings are interpreted within a theoretical framework of embodied emotions. PMID:27695424

  8. Being Moved by Unfamiliar Sad Music Is Associated with High Empathy

    PubMed Central

    Eerola, Tuomas; Vuoskoski, Jonna K.; Kautiainen, Hannu

    2016-01-01

    The paradox of enjoying listening to music that evokes sadness is yet to be fully understood. Unlike prior studies that have explored potential explanations related to lyrics, memories, and mood regulation, we investigated the types of emotions induced by unfamiliar, instrumental sad music, and whether these responses are consistently associated with certain individual difference variables. One hundred and two participants were drawn from a representative sample to minimize self-selection bias. The results suggest that the emotional responses induced by unfamiliar sad music could be characterized in terms of three underlying factors: Relaxing sadness, Moving sadness, and Nervous sadness. Relaxing sadness was characterized by felt and perceived peacefulness and positive valence. Moving sadness captured an intense experience that involved feelings of sadness and being moved. Nervous sadness was associated with felt anxiety, perceived scariness and negative valence. These interpretations were supported by indirect measures of felt emotion. Experiences of Moving sadness were strongly associated with high trait empathy and emotional contagion, but not with other previously suggested traits such as absorption or nostalgia-proneness. Relaxing sadness and Nervous sadness were not significantly predicted by any of the individual difference variables. The findings are interpreted within a theoretical framework of embodied emotions.

  9. Iron K-Alpha Lines from Ionized Discs in Z-Type X-Ray

    NASA Astrophysics Data System (ADS)

    Brandt, W. M.; Matt, G.

    1994-06-01

    The properties of the iron Kα line emitted by a photoionized accretion disc in a Z-type X-ray binary system are determined for different values of the mass accretion rate and disc inclination angle. We consider a geometry where the accretion disc is illuminated by X-rays emitted from a spherical, optically thick Comptonized cloud, representing the magnetosphere on the horizontal branch, and the magnetosphere plus puffed accretion disc on the normal and flaring branches. We find that line profiles can be complex due to Doppler, relativistic, shadowing, line-blending, resonant trapping and other effects. The iron Kα line equivalent width, intrinsic width and centroid energy vary in a tortuous manner as a function of the accretion rate, cloud radius and inclination angle. We examine the reasons for this behaviour and discuss how it will affect inferences about the physical states of Z-sources based on their iron line properties. We compare our results with available data, in particular on Cygnus X-2, and indicate how tests of Z-source models could be made using high-energy-resolution measurements like those expected from AS CA.

  10. Giant planet formation in radially structured protoplanetary discs

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    Our recent N-body simulations of planetary system formation, incorporating models for the main physical processes thought to be important during the building of planets (i.e. gas disc evolution, migration, planetesimal/boulder accretion, gas accretion on to cores, etc.), have been successful in reproducing some of the broad features of the observed exoplanet population (e.g. compact systems of low-mass planets, hot Jupiters), but fail completely to form any surviving cold Jupiters. The primary reason for this failure is rapid inward migration of growing protoplanets during the gas accretion phase, resulting in the delivery of these bodies on to orbits close to the star. Here, we present the results of simulations that examine the formation of gas giant planets in protoplanetary discs that are radially structured due to spatial and temporal variations in the effective viscous stresses, and show that such a model results in the formation of a population of cold gas giants. Furthermore, when combined with models for disc photoevaporation and a central magnetospheric cavity, the simulations reproduce the well-known hot-Jupiter/cold-Jupiter dichotomy in the observed period distribution of giant exoplanets, with a period valley between 10 and 100 d.

  11. Pre-main-sequence accretion and the formation of multiple populations in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Antona, Francesca; Ventura, Paolo; Decressin, Thibaut; Vesperini, Enrico; D'Ercole, Annibale

    2014-10-01

    We investigate the viability of a model in which the chemical anomalies among globular cluster stars are due to accretion of gas on to the protostellar discs of low-mass stars. This model has been suggested as a way to reduce the large initial cluster masses required by other models for the formation of multiple stellar generations. We numerically follow the evolution of the accreting stars, and we show that the structure of the seed star does not remain fully convective for the whole duration of the accretion phase. Stellar populations showing discrete abundances of helium in the core, that seem to be present in some clusters, might be formed with this mechanism only if accretion occurs before the core of the stars become radiative (within 2-3 Myr) or if a thermohaline instability is triggered, to achieve full mixing after the accretion phase ends. We also show that the lithium abundances in accreted structures may vary by orders of magnitude in equal masses obtained by accreting different masses. In addition, the same thermohaline mixing which could provide a homogeneous helium distribution down to the stellar centre, would destroy any lithium surviving in the envelope, so that both helium homogeneity and lithium survival require that the accretion phase be limited to the first couple of million years of the cluster evolution. Such a short accretion phase strongly reduces the amount of processed matter available, and reintroduces the requirement of an extremely large initial mass for the protocluster.

  12. Circumplanetary disc or circumplanetary envelope?

    NASA Astrophysics Data System (ADS)

    Szulágyi, J.; Masset, F.; Lega, E.; Crida, A.; Morbidelli, A.; Guillot, T.

    2016-08-01

    We present three-dimensional simulations with nested meshes of the dynamics of the gas around a Jupiter mass planet with the JUPITER and FARGOCA codes. We implemented a radiative transfer module into the JUPITER code to account for realistic heating and cooling of the gas. We focus on the circumplanetary gas flow, determining its characteristics at very high resolution (80 per cent of Jupiter's diameter). In our nominal simulation where the temperature evolves freely by the radiative module and reaches 13000 K at the planet, a circumplanetary envelope was formed filling the entire Roche lobe. Because of our equation of state is simplified and probably overestimates the temperature, we also performed simulations with limited maximal temperatures in the planet region (1000, 1500, and 2000 K). In these fixed temperature cases circumplanetary discs (CPDs) were formed. This suggests that the capability to form a CPD is not simply linked to the mass of the planet and its ability to open a gap. Instead, the gas temperature at the planet's location, which depends on its accretion history, plays also fundamental role. The CPDs in the simulations are hot and cooling very slowly, they have very steep temperature and density profiles, and are strongly sub-Keplerian. Moreover, the CPDs are fed by a strong vertical influx, which shocks on the CPD surfaces creating a hot and luminous shock-front. In contrast, the pressure supported circumplanetary envelope is characterized by internal convection and almost stalled rotation.

  13. Rumination on Anger and Sadness in Adolescence: Fueling of Fury and Deepening of Despair

    ERIC Educational Resources Information Center

    Peled, Maya; Moretti, Marlene M.

    2007-01-01

    We examined anger rumination and sadness rumination in clinic-referred adolescents (N = 121). Factor analysis indicated that items from analogous anger and sadness rumination measures loaded onto 2 factors tapping anger rumination and sadness rumination, respectively. Structural equation modeling confirmed unique relations between each form of…

  14. A carbon dwarf wearing a Necklace: first proof of accretion in a post-common-envelope binary central star of a planetary nebula with jets

    NASA Astrophysics Data System (ADS)

    Miszalski, Brent; Boffin, Henri M. J.; Corradi, Romano L. M.

    2013-01-01

    The formation of collimated outflows or jets in planetary nebulae (PNe) is not well understood. There is no evidence for active accretion discs in PNe, making it difficult to decide which of the several proposed jet formation scenarios may be correct. A handful of wide binary central stars of PNe are known to have accreted carbon and slow neutron capture (s-process) enhanced material, the immediate progenitors of barium stars; however, no close binary analogues are known to have passed through a common-envelope (CE) phase. Here we present spectroscopy of the Necklace taken near light-curve minimum that for the first time reveals a carbon-rich (C/O > 1) companion, a carbon dwarf, in a post-CE central star. As unevolved stars do not produce carbon, the chemical enhancement of the secondary can only be explained by accretion from the primary. Accretion most likely happened prior to the CE phase via wind accretion as not enough material can be accreted during the short CE phase. The pair of jets in the Necklace, which are observed to be older than the PN, are therefore likely to have been launched from an accretion disc around the companion during this early accretion phase. This discovery adds significant weight to the emerging scenario that jets in post-CE PNe are primarily launched by an accretion disc around a main-sequence companion before the CE phase.

  15. Effect of Be disc evolution on global one-armed oscillations

    NASA Astrophysics Data System (ADS)

    Oktariani, F.; Okazaki, A. T.; Kunjaya, C.; Aprilia

    2016-07-01

    We study the effect of density distribution evolution on the global one-armed oscillation modes in low-viscosity discs around isolated and binary Be stars. Observations show that some Be stars exhibit evidence of formation and dissipation of the equatorial disc. In this paper, we first calculate the density evolution in discs around isolated Be stars. To model the formation stage of the disc, we inject mass at a radius just outside the star at a constant rate for 30-50 yr. As the disc develops, the density distribution approaches the form of the steady disc solution. Then, we turn-off the mass injection to model the disc dissipation stage. The innermost part of the disc starts accretion, and a gap forms between the star and the disc. Next, we calculate the one-armed modes at several epochs. We neglect the effect of viscosity because the time-scale of oscillations is much shorter than the disc evolution time-scale for low viscosity. In the disc formation stage, the eigenfrequency increases with time towards the value for the steady state disc. On the other hand, one-armed eigenmodes in dissipating Be discs have significantly higher eigenfrequencies and narrower propagation regions. Observationally, such a change of mode characteristics can be taken as an evidence for gap opening around the star. In binary Be stars, the characteristics of the disc evolution and the eigenmodes are qualitatively the same as in isolated Be stars, but quantitatively, they have shorter evolution time-scales and higher eigenfrequencies, which is in agreement with the observed trend.

  16. Line-driven ablation of circumstellar discs - I. Optically thin decretion discs of classical Oe/Be stars

    NASA Astrophysics Data System (ADS)

    Kee, Nathaniel Dylan; Owocki, Stanley; Sundqvist, J. O.

    2016-05-01

    discussion of future extensions to study line-driven ablation of denser, optically thick, accretion discs of pre-main-sequence massive stars.

  17. Line-driven ablation of circumstellar discs – I. Optically thin decretion discs of classical Oe/Be stars

    PubMed Central

    Kee, Nathaniel Dylan; Owocki, Stanley; Sundqvist, J. O.

    2016-01-01

    discussion of future extensions to study line-driven ablation of denser, optically thick, accretion discs of pre-main-sequence massive stars. PMID:27346978

  18. Herniated Lumbar Disc

    MedlinePlus

    ... 50. A herniated lumbar disc may also cause back pain, although back pain alone (without leg pain) can have many causes ... 90% success); surgery is less effective in relieving back pain. Nonsurgical treatment Your doctor may prescribe nonsurgical treatments ...

  19. 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.

  20. Hot Accretion Disks Revisited

    NASA Astrophysics Data System (ADS)

    Bjoernsson, Gunnlaugur; Abramowicz, Marek A.; Chen, Xingming; Lasota, Jean-Pierre

    1996-08-01

    All previous studies of hot (Tp 1010-1012 K), optically thin accretion disks have neglected either the presence of e+ e- pairs or advective cooling. Thus all hot disk models constructed previously have not been self-consistent. In this paper we calculate local disk models including pair physics, relevant radiative processes in the hot plasma, and the effect of advective cooling. We use a modification of the Björnsson & Svensson mapping method. We find that the role of e+ e- pairs in the structure of hot, optically thin accretion disks is far less significant than was previously thought. The improved description of the radiation-matter interactions provided in the present paper modify the previously obtained values of the critical parameters characterizing advectively dominated flows.

  1. 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.

  2. Patterns of disc-jet-wind coupling in black hole binaries

    NASA Astrophysics Data System (ADS)

    Fender, R.

    2015-07-01

    In this talk I will present the current state of the art in our understanding of the connection between accretion state and feedback in black hole X-ray binaries. In particular I will discuss how the X-ray accretion states, defined by their spectral and temporal properties, relate to phases of the production of relativistic (radio) jets and accretion disc winds. I will furthermore discuss how these patterns of behaviour contribute to the overall kinetic and radiative feedback during an outburst, and how comparable they may be to similar behaviour in neutron star X-ray binaries and supermassive black holes in active galactic nuclei.

  3. Composition of early planetary atmospheres - I. Connecting disc astrochemistry to the formation of planetary atmospheres

    NASA Astrophysics Data System (ADS)

    Cridland, A. J.; Pudritz, R. E.; Alessi, M.

    2016-09-01

    We present a model of the early chemical composition and elemental abundances of planetary atmospheres based on the cumulative gaseous chemical species that are accreted on to planets forming by core accretion from evolving protoplanetary discs. The astrochemistry of the host disc is computed using an ionization-driven, non-equilibrium chemistry network within viscously evolving disc models. We accrete gas giant planets whose orbital evolution is controlled by planet traps using the standard core accretion model and track the chemical composition of the material that is accreted on to the protoplanet. We choose a fiducial disc model and evolve planets in three traps - water ice line, dead zone and heat transition. For a disc with a lifetime of 4.1 Myr, we produce two hot Jupiters (M = 1.43, 2.67 MJupiter, r = 0.15, 0.11 au) in the heat transition and ice line trap and one failed core (M = 0.003 MJupiter, r = 3.7 au) in the dead zone. These planets are found with mixing ratios for CO and H2O of 1.99 × 10-4 and 5.0 × 10-4, respectively, for both hot Jupiters. Additionally, for these planets we find CO2 and CH4, with mixing ratios of 1.8 × 10-6 → 9.8 × 10-10 and 1.1 × 10-8 → 2.3 × 10-10, respectively. These ranges correspond well with the mixing ratio ranges that have been inferred through the detection of emission spectra from hot Jupiters by multiple authors. We compute a carbon-to-oxygen ratio of 0.227 for the ice line planet and 0.279 for the heat transition planet. These planets accreted their gas inside the ice line, hence the sub-solar C/O.

  4. Happy alone? Sad young men in East Asian gay cinema.

    PubMed

    Berry, C

    2000-01-01

    This essay chooses as its texts three films representing contemporary gay male subjects from each of the "three" China's: HK, Taiwan, and the Mainland. Relocating the homoerotic image of the "sad young man," a trope popular from Hollywood rebellion films of the 1950s and 1960s, to contemporary China, I discuss how this masculine icon has been transformed from one of heroic rebellion to one of existential isolation. Indeed, as the politics of both the outmoded Confucian family and fractured Chinese nationhood intersect, what the sad young (gay) man rebels against is a political fluctuation which is no longer fixed; as the young man's opposition is no longer fixed, so too does he become alienated even from his own rebellious cause. PMID:11133131

  5. Happy alone? Sad young men in East Asian gay cinema.

    PubMed

    Berry, C

    2000-01-01

    This essay chooses as its texts three films representing contemporary gay male subjects from each of the "three" China's: HK, Taiwan, and the Mainland. Relocating the homoerotic image of the "sad young man," a trope popular from Hollywood rebellion films of the 1950s and 1960s, to contemporary China, I discuss how this masculine icon has been transformed from one of heroic rebellion to one of existential isolation. Indeed, as the politics of both the outmoded Confucian family and fractured Chinese nationhood intersect, what the sad young (gay) man rebels against is a political fluctuation which is no longer fixed; as the young man's opposition is no longer fixed, so too does he become alienated even from his own rebellious cause.

  6. 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. PMID:18826928

  7. 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.

  8. Accretion disk coronae

    NASA Technical Reports Server (NTRS)

    White, N. E.; Holt, S. S.

    1981-01-01

    Recent observations of partial X-ray eclipses from 4U1822-37 have shown that the central X-ray source in this system is diffused by a large Compton-thick accretion disk corona (ADC). Another binary, 4U2129-47, also displays a partial eclipse and contains an ADC. The possible origin of an ADC is discussed and a simple hydrostatic evaporated ADC model is developed which, when applied to 4U1822-37, 4U2129+47 and Cyg X-3, can explain their temporal and spectral properties. The quasi-sinusoidal modulation of all three sources can be reconciled with the partial occultation of the ADC by a bulge at the edge of the accretion disk which is caused by the inflowing material. The height of this bulge is an order of magnitude larger than the hydrostatic disk height and is the result of turbulence in the outer region of the disk. The spectral properties of all three sources can be understood in terms of Compton scattering of the original source spectrum by the ADC. Spectral variations with epoch in Cyg X-3 are probably caused by changes in the optical depth of the corona. A consequence of our model is that any accreting neutron star X-ray source in a semi-detached binary system which is close to its Eddington limit most likely contains an optically thick ADC.

  9. Observational evidence for matter propagation in accretion flows

    NASA Astrophysics Data System (ADS)

    Revnivtsev, M.; Potter, S.; Kniazev, A.; Burenin, R.; Buckley, D. A. H.; Churazov, E.

    2011-02-01

    We study simultaneous X-ray and optical observations of three intermediate polars, EX Hya, V1223 Sgr and TV Col, with the aim of understanding the propagation of matter in their accretion flows. We show that in all cases the power spectra of the flux variability of binary systems in X-ray and optical bands are similar to each other, and the majority of X-ray and optical fluxes are correlated with time lag <1 s. These findings support the idea that the optical emission of accretion discs in these binary systems largely originates as the reprocessing of the X-ray luminosity of their white dwarfs. In the best obtained data set of EX Hya we see that the optical light curve unambiguously contains some component that leads the X-ray emission by ˜7 s. We interpret this in the framework of the model of propagating fluctuations and thus deduce the time of travel of matter from the innermost part of the truncated accretion disc to the white dwarf surface. This value agrees very well with the time expected for matter threaded on to the magnetosphere of the white dwarf to fall to its surface. The data sets of V1223 Sgr and TV Col in general confirm these findings, but have poorer quality.

  10. New instruments at IPNS: POSY II and SAD II

    SciTech Connect

    Crawford, R.K.; Felcher, G.P.; Kleb, R.; Epperson, J.E.; Thiyagarajan, P.

    1988-09-29

    Three new instruments are currently in varying degrees of development/construction at IPNS. One of these, the Glass, Liquid, and Amorphous Materials Diffractometer (GLAD) is the subject of a separate paper in these Proceedings, and so will not be discussed further here. The other two, a second neutron reflectometer (POSY II) and a second small-angle diffractometer (SAD II) are described briefly below. 5 refs., 1 fig., 1 tab.

  11. Data-collection strategy for challenging native SAD phasing

    PubMed Central

    Olieric, Vincent; Weinert, Tobias; Finke, Aaron D.; Anders, Carolin; Li, Dianfan; Olieric, Natacha; Borca, Camelia N.; Steinmetz, Michel O.; Caffrey, Martin; Jinek, Martin; Wang, Meitian

    2016-01-01

    Recent improvements in data-collection strategies have pushed the limits of native SAD (single-wavelength anomalous diffraction) phasing, a method that uses the weak anomalous signal of light elements naturally present in macromolecules. These involve the merging of multiple data sets from either multiple crystals or from a single crystal collected in multiple orientations at a low X-ray dose. Both approaches yield data of high multiplicity while minimizing radiation damage and systematic error, thus ensuring accurate measurements of the anomalous differences. Here, the combined use of these two strategies is described to solve cases of native SAD phasing that were particular challenges: the integral membrane diacylglycerol kinase (DgkA) with a low Bijvoet ratio of 1% and the large 200 kDa complex of the CRISPR-associated endonuclease (Cas9) bound to guide RNA and target DNA crystallized in the low-symmetry space group C2. The optimal native SAD data-collection strategy based on systematic measurements performed on the 266 kDa multiprotein/multiligand tubulin complex is discussed. PMID:26960129

  12. The effect of sad facial expressions on weight judgment

    PubMed Central

    Weston, Trent D.; Hass, Norah C.; Lim, Seung-Lark

    2015-01-01

    Although the body weight evaluation (e.g., normal or overweight) of others relies on perceptual impressions, it also can be influenced by other psychosocial factors. In this study, we explored the effect of task-irrelevant emotional facial expressions on judgments of body weight and the relationship between emotion-induced weight judgment bias and other psychosocial variables including attitudes toward obese persons. Forty-four participants were asked to quickly make binary body weight decisions for 960 randomized sad and neutral faces of varying weight levels presented on a computer screen. The results showed that sad facial expressions systematically decreased the decision threshold of overweight judgments for male faces. This perceptual decision bias by emotional expressions was positively correlated with the belief that being overweight is not under the control of obese persons. Our results provide experimental evidence that task-irrelevant emotional expressions can systematically change the decision threshold for weight judgments, demonstrating that sad expressions can make faces appear more overweight than they would otherwise be judged. PMID:25914669

  13. Boundary between stable and unstable regimes of accretion. Ordered and chaotic unstable regimes

    NASA Astrophysics Data System (ADS)

    Blinova, A. A.; Romanova, M. M.; Lovelace, R. V. E.

    2016-07-01

    We present a new study of the Rayleigh-Taylor unstable regime of accretion on to rotating magnetized stars in a set of high grid resolution three-dimensional magnetohydrodynamic simulations performed in low-viscosity discs. We find that the boundary between the stable and unstable regimes is determined almost entirely by the fastness parameter ωs = Ω⋆/ΩK(rm), where Ω⋆ is the angular velocity of the star and ΩK(rm) is the angular velocity of the Keplerian disc at the disc-magnetosphere boundary r = rm. We found that accretion is unstable if ωs ≲ 0.6. Accretion through instabilities is present in stars with different magnetospheric sizes. However, only in stars with relatively small magnetospheres, rm/R⋆ ≲ 7, do the unstable tongues produce chaotic hotspots on the stellar surface and irregular light curves. At even smaller values of the fastness parameter, ωs ≲ 0.45, multiple irregular tongues merge, forming one or two ordered unstable tongues that rotate with the angular frequency of the inner disc. This transition occurs in stars with even smaller magnetospheres, rm/R⋆ ≲ 4.2. Most of our simulations were performed at a small tilt of the dipole magnetosphere, Θ = 5°, and a small viscosity parameter α = 0.02. Test simulations at higher α values show that many more cases become unstable, and the light curves become even more irregular. Test simulations at larger tilts of the dipole Θ show that instability is present, however, accretion in two funnel streams dominates if Θ ≳ 15°. The results of these simulations can be applied to accreting magnetized stars with relatively small magnetospheres: Classical T Tauri stars, accreting millisecond X-ray pulsars, and cataclysmic variables.

  14. Going with the flow: using gas clouds to probe the accretion flow feeding Sgr A*

    NASA Astrophysics Data System (ADS)

    McCourt, Michael; Madigan, Ann-Marie

    2016-01-01

    The massive black hole in our Galactic centre, Sgr A*, accretes only a small fraction of the gas available at its Bondi radius. The physical processes determining this accretion rate remain unknown, partly due to a lack of observational constraints on the gas at distances between ˜10 and ˜105 Schwarzschild radii (Rs) from the black hole. Recent infrared observations identify low-mass gas clouds, G1 and G2, moving on highly eccentric, nearly co-planar orbits through the accretion flow around Sgr A*. Although it is not yet clear whether these objects contain embedded stars, their extended gaseous envelopes evolve independently as gas clouds. In this paper we attempt to use these gas clouds to constrain the properties of the accretion flow at ˜103 Rs. Assuming that G1 and G2 follow the same trajectory, we model the small differences in their orbital parameters as evolution resulting from interaction with the background flow. We find evolution consistent with the G-clouds originating in the clockwise disc. Our analysis enables the first unique determination of the rotation axis of the accretion flow: we localize the rotation axis to within 20°, finding an orientation consistent with the parsec-scale jet identified in X-ray observations and with the circumnuclear disc, a massive torus of molecular gas ˜1.5 pc from Sgr A*. This suggests that the gas in the accretion flow comes predominantly from the circumnuclear disc, rather than the winds of stars in the young clockwise disc. This result will be tested by the Event-Horizon Telescope within the next year. Our model also makes testable predictions for the orbital evolution of G1 and G2, falsifiable on a 5-10 year time-scale.

  15. High-redshift clumpy discs and bulges in cosmological simulations

    NASA Astrophysics Data System (ADS)

    Ceverino, Daniel; Dekel, Avishai; Bournaud, Frederic

    2010-06-01

    We analyse the first cosmological simulations that recover the fragmentation of high-redshift galactic discs driven by cold streams. The fragmentation is recovered owing to an AMR resolution better than 70pc with cooling below 104K. We study three typical star-forming galaxies in haloes of ~5 × 1011Msolar at z ~= 2.3 when they were not undergoing a major merger. The steady gas supply by cold streams leads to gravitationally unstable, turbulent discs, which fragment into giant clumps and transient features on a dynamical time-scale. The disc clumps are not associated with dark-matter haloes. The clumpy discs are self-regulated by gravity in a marginally unstable state. Clump migration and angular-momentum transfer on an orbital time-scale help the growth of a central bulge with a mass comparable to the disc. The continuous gas input keeps the system of clumpy disc and bulge in a near steady state for several Gyr. The average star formation rate, much of which occurs in the clumps, follows the gas accretion rate of ~45Msolaryr-1. The simulated galaxies resemble in many ways the observed star-forming galaxies at high redshift. Their properties are consistent with the simple theoretical framework presented in Dekel, Sari & Ceverino. In particular, a two-component analysis reveals that the simulated discs are indeed marginally unstable, and the time evolution confirms the robustness of the clumpy configuration in a cosmological steady state. By z ~ 1, the simulated systems are stabilized by a dominant stellar spheroid, demonstrating the process of `morphological quenching' of star formation. We demonstrate that the disc fragmentation is not a numerical artefact once the Jeans length is kept larger than nearly seven resolution elements, i.e. beyond the standard Truelove criterion.

  16. Chaotic cold accretion on to black holes in rotating atmospheres

    NASA Astrophysics Data System (ADS)

    Gaspari, M.; Brighenti, F.; Temi, P.

    2015-07-01

    The fueling of black holes is one key problem in the evolution of baryons in the universe. Chaotic cold accretion (CCA) profoundly differs from classic accretion models, as Bondi and thin disc theories. Using 3D high-resolution hydrodynamic simulations, we now probe the impact of rotation on the hot and cold accretion flow in a typical massive galaxy. In the hot mode, with or without turbulence, the pressure-dominated flow forms a geometrically thick rotational barrier, suppressing the black hole accretion rate to ~1/3 of the spherical case value. When radiative cooling is dominant, the gas loses pressure support and quickly circularizes in a cold thin disk; the accretion rate is decoupled from the cooling rate, although it is higher than that of the hot mode. In the more common state of a turbulent and heated atmosphere, CCA drives the dynamics if the gas velocity dispersion exceeds the rotational velocity, i.e., turbulent Taylor number Tat< 1. Extended multiphase filaments condense out of the hot phase via thermal instability (TI) and rain toward the black hole, boosting the accretion rate up to 100 times the Bondi rate (Ṁ• ~ Ṁcool). Initially, turbulence broadens the angular momentum distribution of the hot gas, allowing the cold phase to condense with prograde or retrograde motion. Subsequent chaotic collisions between the cold filaments, clouds, and a clumpy variable torus promote the cancellation of angular momentum, leading to high accretion rates. As turbulence weakens (Tat > 1), the broadening of the distribution and the efficiency of collisions diminish, damping the accretion rate ∝ Tat-1, until the cold disk drives the dynamics. This is exacerbated by the increased difficulty to grow TI in a rotating halo. The simulated sub-Eddington accretion rates cover the range inferred from AGN cavity observations. CCA predicts inner flat X-ray temperature and r-1 density profiles, as recently discovered in M 87 and NGC 3115. The synthetic Hα images

  17. Disc instability models for X-ray transients: evidence for evaporation and low α-viscosity?

    NASA Astrophysics Data System (ADS)

    Menou, Kristen; Hameury, Jean-Marie; Lasota, Jean-Pierre; Narayan, Ramesh

    2000-05-01

    We construct time-dependent models of accretion discs around black holes and neutron stars. We investigate the effect that evaporation of the inner disc regions during quiescence has upon the predictions of the disc instability model (DIM) for these systems. We do not include irradiation of the disc in the models. Removing the inner, most unstable, parts of the accretion disc increases the predicted recurrence times. However, DIMs with values of the viscosity parameter αhot~0.1 and αcold~0.02 (values typically used in applications of the DIM to standard dwarf nova outbursts) fail to reproduce the long recurrence times of soft X-ray transients (unless we resort to fine-tuning the parameters), independent of the evaporation strength. We show that models in which evaporation is included and a smaller value of αcold (~0.005) used do reproduce the long recurrence times and the accretion rates at the level of the Eddington rate observed in outburst. The large difference between the values of αhot and αcold, if confirmed once disc irradiation is included, suggests that several viscosity mechanisms operate in these accretion discs. For some parameter sets our models predict re-flares during the decline from outburst. The re-flares are a physical property of the model and result from the formation of a heating front in the wake of an initial cooling front, and subsequent multiple front reflections. The re-flares disappear in low-α models where front reflection cannot occur.

  18. Thanatology in protoplanetary discs. The combined influence of Ohmic, Hall, and ambipolar diffusion on dead zones

    NASA Astrophysics Data System (ADS)

    Lesur, Geoffroy; Kunz, Matthew W.; Fromang, Sébastien

    2014-06-01

    Protoplanetary discs are poorly ionised due to their low temperatures and high column densities and are therefore subject to three "non-ideal" magnetohydrodynamic (MHD) effects: Ohmic dissipation, ambipolar diffusion, and the Hall effect. The existence of magnetically driven turbulence in these discs has been a central question since the discovery of the magnetorotational instability (MRI). Early models considered Ohmic diffusion only and led to a scenario of layered accretion, in which a magnetically "dead" zone in the disc midplane is embedded within magnetically "active" surface layers at distances of about 1-10 au from the central protostellar object. Recent work has suggested that a combination of Ohmic dissipation and ambipolar diffusion can render both the midplane and surface layers of the disc inactive and that torques due to magnetically driven outflows are required to explain the observed accretion rates. We reassess this picture by performing three-dimensional numerical simulations that include all three non-ideal MHD effects for the first time. We find that the Hall effect can generically "revive" dead zones by producing a dominant azimuthal magnetic field and a large-scale Maxwell stress throughout the midplane, provided that the angular velocity and magnetic field satisfy Ω·B > 0. The attendant large magnetic pressure modifies the vertical density profile and substantially increases the disc scale height beyond its hydrostatic value. Outflows are produced but are not necessary to explain accretion rates ≲ 10-7 M⊙ yr-1. The flow in the disc midplane is essentially laminar, suggesting that dust sedimentation may be efficient. These results demonstrate that if the MRI is relevant for driving mass accretion in protoplanetary discs, one must include the Hall effect to obtain even qualitatively correct results. Appendices are available in electronic form at http://www.aanda.org

  19. Launching jets from accretion belts

    NASA Astrophysics Data System (ADS)

    Schreier, Ron; Soker, Noam

    2016-05-01

    We propose that sub-Keplerian accretion belts around stars might launch jets. The sub-Keplerian inflow does not form a rotationally supported accretion disk, but it rather reaches the accreting object from a wide solid angle. The basic ingredients of the flow are a turbulent region where the accretion belt interacts with the accreting object via a shear layer, and two avoidance regions on the poles where the accretion rate is very low. A dynamo that is developed in the shear layer amplifies magnetic fields to high values. It is likely that the amplified magnetic fields form polar outflows from the avoidance regions. Our speculative belt-launched jets model has implications on a rich variety of astrophysical objects, from the removal of common envelopes to the explosion of core collapse supernovae by jittering jets.

  20. Accreting X-ray Pulsars

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2009-01-01

    This presentation describes the behavior of matter in environments with extreme magnetic and gravitational fields, explains the instability/stability of accretion disks in certain systems, and discusses how emergent radiation affects accretion flow. Magnetic field measurements are obtained by measuring the lowest cyclotron absorption line energy, observing the cutoff of accretion due to centrifugal inhibition and measuring the spin-up rate at high luminosity.

  1. 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.

  2. Active states and structure transformations in accreting white dwarfs

    NASA Astrophysics Data System (ADS)

    Boneva, Daniela; Kaygorodov, Pavel

    2016-07-01

    Active states in white dwarfs are usually associated with light curve's effects that concern to the bursts, flickering or flare-up occurrences. It is common that a gas-dynamics source exists for each of these processes there. We consider the white dwarf binary stars with accretion disc around the primary. We suggest a flow transformation modeling of the mechanisms that are responsible for ability to cause some flow instability and bring the white dwarfs system to the outburst's development. The processes that cause the accretion rate to sufficiently increase are discussed. Then the transition from a quiescent to an active state is realized. We analyze a quasi-periodic variability in the luminosity of white dwarf binary stars systems. The results are supported with an observational data.

  3. Isolated Optic Disc Tuberculosis

    PubMed Central

    Mansour, Ahmad M.; Tabbara, Khalid F.; Tabbarah, Zuhair

    2015-01-01

    We present a healthy male subject who developed progressive visual loss in the left eye initially diagnosed as optic neuritis. Upon suspicion of infectious etiology, testing was positive for tuberculosis. There were no signs or symptoms of active systemic tuberculosis infection. The patient responded swiftly to antimycobacterial therapy with return of vision and resolution of disc swelling. Positive purified protein derivative skin test, negative chest radiograph, negative systemic workup, negative workup for other causes of unilateral optic neuritis and quick response to mycobacterial therapy reaffirm the entity of isolated optic disc tuberculosis similar to isolated choroidal tuberculosis without systemic manifestation. PMID:26483675

  4. Accretion mode of the ultraluminous X-ray source M82 X-2

    NASA Astrophysics Data System (ADS)

    Karino, S.; Miller, J. C.

    2016-11-01

    Periodic pulsations have been found in emission from the ultraluminous X-ray source M82 X-2, strongly suggesting that the emitter is a rotating neutron star rather than a black hole. However, the radiation mechanisms and accretion mode involved have not yet been clearly established. In this paper, we examine the applicability to this object of standard accretion modes for high mass X-ray binaries (HMXBs). We find that spherical wind accretion, which drives OB-type HMXBs, cannot apply here but that there is a natural explanation in terms of an extension of the picture for standard Be-type HMXBs. We show that a neutron star with a moderately strong magnetic field, accreting from a disc-shaped wind emitted by a Be-companion, could be compatible with the observed relation between spin and orbital period. A Roche lobe overflow picture is also possible under certain conditions.

  5. Disc-corona energetics in the very high state of Galactic black holes

    NASA Astrophysics Data System (ADS)

    Done, Chris; Kubota, Aya

    2006-09-01

    The X-ray spectra of Galactic binary systems dominated by a quasi-thermal component (disc dominated or high/soft state) are well described by a standard Shakura-Sunyaev disc structure down to the last stable orbit around the black hole. This is not the case in the very high (or steep power-law) state, where the X-ray spectra show both a strong disc component and strong, steep tail to higher energies. We use two such spectra from the black hole transient XTE J1550-564 as specific examples of this state, where the power emitted in the tail is more than 50 per cent of the bolometric luminosity. The simultaneous ASCA and RXTE data show that these have disc spectra which are significantly lower in temperature than those seen from the same source at the same luminosity in the high/soft state. If these give a true picture of the disc, then either the disc emissivity has reduced, and/or the disc truncates above the last stable orbit. However, it is often assumed that the tail is produced by Compton scattering, in which case its shape in these spectra requires that the Comptonizing region is marginally optically thick (τ ~ 2-3), and covers a large fraction of the inner disc. This will distort our view of the disc, especially of the hottest-temperature material. We build a theoretical model of a Comptonizing corona over an inner disc, and fit this to the data, but find that it still requires a large increase in inner disc radius for a standard disc emissivity. Instead, it seems more probable that the disc emissivity changes in the presence of the corona. We implement the specific inner disc-corona coupling model of Svensson & Zdziarski, in which some fraction f of the accretion power is dissipated in the corona, leaving only a fraction 1 - f to be dissipated in the optically thick disc. We show that this can explain the low-temperature/high-luminosity disc emission seen in the very high state with only a small increase in radius of the disc. While this inferred disc

  6. Intrinsic disc emission and the soft X-ray excess in active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Done, Chris; Davis, S. W.; Jin, C.; Blaes, O.; Ward, M.

    2012-03-01

    Narrow-line Seyfert 1 (NLS1) galaxies have low-mass black holes and mass accretion rates close to (or exceeding) Eddington, so a standard blackbody accretion disc should peak in the extreme ultraviolet. However, the lack of true absorption opacity in the disc means that the emission is better approximated by a colour temperature corrected blackbody, and this colour temperature correction is large enough (˜2.4) that the bare disc emission from a zero spin black hole can extend into the soft X-ray bandpass. Part of the soft X-ray excess seen in these objects must be intrinsic emission from the disc unless the vertical structure is very different to that predicted. None the less, this is not the whole story even for the extreme NLS1 as the shape of the soft excess is much broader than predicted by a bare disc spectrum, indicating some Compton upscattering by warm, optically thick material. We associate this with the disc itself, so it must ultimately be powered by mass accretion. We build an energetically self-consistent model assuming that the emission thermalizes to a (colour temperature corrected) blackbody only at large radii. At smaller radii the gravitational energy is split between powering optically thick Comptonized disc emission (forming the soft X-ray excess) and an optically thin corona above the disc (forming the tail to higher energies). We show examples of this model fit to the extreme NLS1 RE J1034+396, and to the much lower Eddington fraction broad-line Seyfert 1 PG 1048+231. We use these to guide our fits and interpretations of three template spectra made from co-adding multiple sources to track out a sequence of active galactic nucleus (AGN) spectra as a function of L/LEdd. Both the individual objects and template spectra show the surprising result that the Compton upscattered soft X-ray excess decreases in importance with increasing L/LEdd. The strongest soft excesses are associated with low mass accretion rate AGN rather than being tied to some

  7. 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.

  8. Global Time Dependent Solutions of Stochastically Driven Standard Accretion Disks: Development of Hydrodynamical Code

    NASA Astrophysics Data System (ADS)

    Wani, Naveel; Maqbool, Bari; Iqbal, Naseer; Misra, Ranjeev

    2016-07-01

    X-ray binaries and AGNs are powered by accretion discs around compact objects, where the x-rays are emitted from the inner regions and uv emission arise from the relatively cooler outer parts. There has been an increasing evidence that the variability of the x-rays in different timescales is caused by stochastic fluctuations in the accretion disc at different radii. These fluctuations although arise in the outer parts of the disc but propagate inwards to give rise to x-ray variability and hence provides a natural connection between the x-ray and uv variability. There are analytical expressions to qualitatively understand the effect of these stochastic variabilities, but quantitative predictions are only possible by a detailed hydrodynamical study of the global time dependent solution of standard accretion disc. We have developed numerical efficient code (to incorporate all these effects), which considers gas pressure dominated solutions and stochastic fluctuations with the inclusion of boundary effect of the last stable orbit.

  9. Parker winds revisited: an extension to disc winds

    NASA Astrophysics Data System (ADS)

    Waters, Timothy R.; Proga, Daniel

    2012-11-01

    A simple 1D dynamical model of thermally driven disc winds is proposed, based on the results of recent, 2.5D axisymmetric simulations. Our formulation of the disc wind problem is in the spirit of the original Parker and Bondi problems, namely we assume an elementary flow configuration consisting of an outflow following pre-defined trajectories in the presence of a central gravitating point mass. Viscosity and heat conduction are neglected. We consider two different streamline geometries, both comprised of straight lines in the (x, z)-plane: (i) streamlines that converge to a geometric point located at (x, z) = (0, -d) and (ii) streamlines that emerge at a constant inclination angle from the disc mid-plane (the x-axis, as we consider geometrically thin accretion discs). The former geometry is commonly used in kinematic models to compute synthetic spectra, while the latter, which exhibits self-similarity, is likely unused for this purpose, although it easily can be with existing kinematic models. We make the case that it should be, i.e. geometry (ii) leads to transonic wind solutions with substantially different properties owing to its lack of streamline divergence. Both geometries can be used to complement recent efforts to estimate photoevaporative mass-loss rates from protoplanetary discs. Pertinent to understanding our disc wind results, which are also applicable to X-ray binaries and active galactic nuclei, is a focused discussion on lesser known properties of classic Parker wind solutions. We find that the parameter space corresponding to decelerating Parker wind solutions is made larger due to rotation and leads instead to disc wind solutions that always accelerate after the bulk velocity is slowed to a minimum value. Surprisingly, Keplerian rotation may allow for two different transonic wind solutions for the same physical conditions.

  10. A SCUBA-2 850-μm survey of protoplanetary discs in the IC 348 cluster

    NASA Astrophysics Data System (ADS)

    Cieza, L.; Williams, J.; Kourkchi, E.; Andrews, S.; Casassus, S.; Graves, S.; Schreiber, M. R.

    2015-12-01

    We present 850-μm observations of the 2-3 Myr cluster IC 348 in the Perseus molecular cloud using the SCUBA-2 camera on the James Clerk Maxwell Telescope. Our SCUBA-2 map has a diameter of 30 arcmin and contains ˜370 cluster members, including ˜200 objects with IR excesses. We detect a total of 13 discs. Assuming standard dust properties and a gas-to-dust-mass ratio of 100, we derive disc masses ranging from 1.5 to 16 MJUP. We also detect six Class 0/I protostars. We find that the most massive discs (MD > 3 MJUP; 850-μm flux > 10 mJy) in IC 348 tend to be transition objects according to the characteristic `dip' in their infrared spectral energy distributions (SEDs). This trend is also seen in other regions. We speculate that this could be an initial conditions effect (e.g. more massive discs tend to form giant planets that result in transition disc SEDs) and/or a disc evolution effect (the formation of one or more massive planets results in both a transition disc SED and a reduction of the accretion rate, increasing the lifetime of the outer disc). A stacking analysis of the discs that remain undetected in our SCUBA-2 observations suggests that their median 850-μm flux should be ≲1 mJy, corresponding to a disc mass ≲0.3 MJUP (gas plus dust) or ≲1 M⊕ of dust. While the available data are not deep enough to allow a meaningful comparison of the disc luminosity functions between IC 348 and other young stellar clusters, our results imply that disc masses exceeding the minimum-mass solar nebula are very rare (≲1per cent) at the age of IC 348, especially around very low-mass stars.

  11. The accretion regimes of a highly magnetized NS: the unique case of NuSTAR J095551+6940.8

    NASA Astrophysics Data System (ADS)

    Dall'Osso, Simone; Perna, Rosalba; Papitto, Alessandro; Bozzo, Enrico; Stella, Luigi

    2016-04-01

    The ultraluminous accreting pulsar M82-X2 (NuSTAR J095551+6940.8) offers an unprecedented opportunity to study the disc-magnetosphere interaction in a new regime of supercritical accretion. The source X-ray emission has been highly variable during the last 15 yrs. It ranged from a maximum of ˜2 × 1040 erg s-1 through intermediate values ˜ a few × 1039 erg s-1, and down to a minimum below 2 × 1038 erg s-1 that we have determined here, by analysing archival Chandra HRC observations of the source at an epoch at which it was undetected. We interpret the source variability via a magnetically threaded disc model: when at peak luminosity, the neutron star (NS) is close to spin equilibrium, its inner disc edge rm ˜ 108 cm is approximately half the corotation radius rco, and radiation pressure dominates the disc out to rtr ≲ 109 cm. In the radiation-pressure-dominated regime, rm grows very slowly as the mass inflow rate drops: as a result, rm < rco remains valid until dot{M} ≳dot{M}_E, the Eddington accretion rate, allowing a wide range of accretion luminosities to the NS. Once dot{M} < dot{M}_E accretion on to the NS is inhibited because rm > rco, and the source luminosity is expected to drop by a large factor. We conclude that a magnetically threaded accretion disc surrounding a highly magnetized NS (B ≲ 1013 G), and transitioning between the radiation-pressure and gas-pressure dominated regimes, offers the best interpretation for all the currently observed properties of NuSTAR J095551+6940.8.

  12. 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.

  13. Revival of the Jumping Disc

    ERIC Educational Resources Information Center

    Ucke, C.; Schlichting, H-J.

    2009-01-01

    Snap discs made of bimetal have many technical applications as thermostats. Jumping discs are a toy version of such snap discs. Besides giving technical information, we describe physical investigations. We show especially how, through simple measurements and calculations, you can determine the initial speed ([approximately equal to]3.5 m…

  14. The Chemistry of Optical Discs.

    ERIC Educational Resources Information Center

    Birkett, David

    2002-01-01

    Explains the chemistry used in compact discs (CD), digital versatile discs (DVD), and magneto-optical (MO) discs focusing on the steps of initial creation of the mold, the molding of the polycarbonate, the deposition of the reflective layers, the lacquering of the CDs, and the bonding of DVDs. (Contains 15 references.) (YDS)

  15. Role of limb brightening in the angular momentum determination of accreting black holes

    NASA Astrophysics Data System (ADS)

    Svoboda, J.

    2009-09-01

    Angular momentum of an accreting black hole can be determined by careful spectroscopy of the emission and absorption features produced in the inner regions of an accretion disc. We discuss the method employing the relativistic line profiles of iron in the X-ray domain, where the emergent spectrum is blurred by general relativistic effects. Accuracy of the spectra fitting can be affected by inappropriate account of the directional distribution of the disc emission. However, most works so far have avoided this issue by fixing a unique profile of the angular distribution, invariable over the entire range of radii in the disc and energy in the spectral band. An isotropic distribution or a particular limb-darkening law have been frequently assumed, although some calculations of the X-ray reflection suggest that the limb brightening would be more appropriate for the accretion disc surface. By assuming a rotating black hole in the centre of an equatorial accretion disc, we perform numerical radiation-transfer computations to determine the directionality of outgoing X-rays in the 2-10 keV energy band. In order to evaluate the feasibility of future angular measurments and their expected constraints with future X-ray data, we produced a set of artificial spectra using a simple model prescription and preliminary response matrix for the IXO mission. We show how sensitive the results of the black-hole angular momentum determination are to the assumptions about the intrinsic directional distribution of the emitted photons. The results depend on the values of the inclination angle and the spin itself. However, we find that the isotropic directionality reproduces our data to the best precision.

  16. The Teddy Bears' Disc.

    ERIC Educational Resources Information Center

    Laurillard, Diana

    1985-01-01

    Reports an evaluation of the Teddy Bear disc, an interactive videodisc developed at the Open University for a second-level course in metallurgy and materials technology. Findings from observation of students utilizing the videodisc are reviewed; successful design features and design problems are considered; and development costs are outlined. (MBR)

  17. On the magnetization of jet-launching discs

    NASA Astrophysics Data System (ADS)

    Tzeferacos, P.; Ferrari, A.; Mignone, A.; Zanni, C.; Bodo, G.; Massaglia, S.

    2009-12-01

    Magnetohydrodynamic models of collimated outflows produced by accretion discs around compact objects can be used for interpreting the phenomenology of active astrophysical objects as young stellar objects, microquasars, X-ray binaries, gamma-ray bursts, extended radio galaxies and active galactic nuclei. In the present work, we discuss how the strength of magnetic fields determines the characteristics of solutions in models where the collimated outflow and the accretion disc are treated consistently. We perform an extensive analysis of the magnetic field's strength by non-relativistic axisymmetric numerical simulations using the PLUTO code. We discuss in detail the characteristics of the numerical solutions with specific reference to the efficiency of transforming accretion inflows into collimated superfast magnetosonic outflows. The relevance of the resistivity parameter used in numerical simulations is analysed. The main results are that magnetic fields around and below equipartition with plasma pressure allow for steady superfast magnetosonic collimated jet solutions; for even lower magnetization, the solutions found are unsteady, with small velocities and matter-dominated magnetic field lines that behave kinematically; magnetic fields above equipartition lead to unsteady sub-Alfvénic winds. These results allow to conclude that stationary super-Alfvénic and superfast magnetosonic outflow solutions are found only for equipartition and weaker magnetic fields, for the range studied in this article.

  18. Misery loves company: when sadness increases the desire for social connectedness.

    PubMed

    Gray, Heather M; Ishii, Keiko; Ambady, Nalini

    2011-11-01

    In three experiments, the authors investigated the effects of sadness on the desire for social connectedness. They hypothesized that sadness serves an adaptive function by motivating people to reach out to others and preferentially attend to information related to one's current level of social connectedness, but only when it is instigated by social loss. Consistent with this hypothesis, the authors observed that sadness induced by an emotional depiction of social loss enhanced (a) attention to nonverbal cues, an important source of information concerning an individual's current level of social connectedness (Experiment 1), and (b) the desire to engage in social behaviors (Experiment 2). In Experiment 3 the authors found that sadness that results from imagined social loss uniquely produced this pattern of effects. Sadness that resulted from imagined failure had different effects on motivation and no effect on sensitivity to nonverbal cues. These results support and refine functional explanations for the universality of sadness.

  19. Disc outflows and high-luminosity true type 2 AGN

    NASA Astrophysics Data System (ADS)

    Elitzur, Moshe; Netzer, Hagai

    2016-06-01

    The absence of intrinsic broad-line emission has been reported in a number of active galactic nuclei (AGN), including some with high Eddington ratios. Such `true type 2 AGN' are inherent to the disc-wind scenario for the broad-line region: broad-line emission requires a minimal column density, implying a minimal outflow rate and thus a minimal accretion rate. Here we perform a detailed analysis of the consequences of mass conservation in the process of accretion through a central disc. The resulting constraints on luminosity are consistent with all the cases where claimed detections of true type 2 AGN pass stringent criteria, and predict that intrinsic broad-line emission can disappear at luminosities as high as ˜4 × 1046 erg s-1 and any Eddington ratio, though more detections can be expected at Eddington ratios below ˜1 per cent. Our results are applicable to every disc outflow model, whatever its details and whether clumpy or smooth, irrespective of the wind structure and its underlying dynamics. While other factors, such as changes in spectral energy distribution or covering factor, can affect the intensities of broad emission lines, within this scenario they can only produce true type 2 AGN of higher luminosity then those prescribed by mass conservation.

  20. On the origin of exponential galaxy discs

    NASA Astrophysics Data System (ADS)

    Dutton, Aaron A.

    2009-06-01

    One of the most important unresolved issues for galaxy formation theory is to understand the origin of exponential galaxy discs. We use a disc galaxy evolution model to investigate whether galaxies with exponential surface brightness profiles can be produced in a cosmologically motivated framework for disc galaxy formation. Our model follows the accretion, cooling and ejection of baryonic mass, as a function of radius, inside growing dark matter haloes. The surface density profile of the disc is determined by detailed angular momentum conservation, starting from the distribution of specific angular momentum as found in cosmological simulations. Exponential and quasi-exponential discs can be produced by our model through a combination of supernova-driven galactic outflows (which preferentially remove low angular momentum material), intrinsic variation in the angular momentum distribution of the halo gas and the inefficiency of star formation at large radii. We use observations from the Sloan Digital Sky Survey (SDSS) New York University Value Added Catalog (NYU-VAGC) to show that the median Sérsic index of late-type galaxies is a strong function of stellar mass. For blue galaxies, low-mass galaxies have n ~= 1.3, while high-mass galaxies have n ~= 4, with a transition mass of Mstar ~= 2.5 × 1010Msolar. Our model with energy-driven outflows correctly reproduces this trend, whereas our models with momentum-driven outflows and no outflows overpredict the Sérsic indices in low-mass galaxies. We show that the observed fraction of `bulge-less' exponential galaxies is a strong function of stellar mass. For Milky Way mass galaxies (Vrot ~= 220kms-1, Mstar ~= 1011Msolar), less than 0.1 per cent of blue galaxies are bulge-less, whereas for M33 mass galaxies (Vrot ~= 120kms-1, Mstar ~= 1010Msolar) bulge-less and quasi-bulge-less galaxies are more common, with 45 per cent of blue galaxies having the Sérsic index n < 1.5. These results suggest that the difficulty of

  1. Characterization of global flow and local fluctuations in 3D SPH simulations of protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Arena, S. E.; Gonzalez, J.-F.

    2013-07-01

    A complete and detailed knowledge of the structure of the gaseous component in protoplanetary discs is essential to the study of dust evolution during the early phases of pre-planetesimal formation. The aim of this paper is to determine if three-dimensional accretion discs simulated by the smoothed particle hydrodynamics (SPH) method can reproduce the observational data now available and the expected turbulent nature of protoplanetary discs. The investigation is carried out by setting up a suite of diagnostic tools specifically designed to characterize both the global flow and the fluctuations of the gaseous disc. The main result concerns the role of the artificial viscosity implementation in the SPH method: in addition to the already known ability of SPH artificial viscosity to mimic a physical-like viscosity under specific conditions, we show how the same artificial viscosity prescription behaves like an implicit turbulence model. In fact, we identify a threshold for the parameters in the standard artificial viscosity above which SPH disc models present a cascade in the power spectrum of velocity fluctuations, turbulent diffusion and a mass accretion rate of the same order of magnitude as measured in observations. Furthermore, the turbulence properties observed locally in SPH disc models are accompanied by meridional circulation in the global flow of the gas, proving that the two mechanisms can coexist.

  2. Recognizing induced emotions of happiness and sadness from dance movement.

    PubMed

    Van Dyck, Edith; Vansteenkiste, Pieter; Lenoir, Matthieu; Lesaffre, Micheline; Leman, Marc

    2014-01-01

    Recent research revealed that emotional content can be successfully decoded from human dance movement. Most previous studies made use of videos of actors or dancers portraying emotions through choreography. The current study applies emotion induction techniques and free movement in order to examine the recognition of emotional content from dance. Observers (N = 30) watched a set of silent videos showing depersonalized avatars of dancers moving to an emotionally neutral musical stimulus after emotions of either sadness or happiness had been induced. Each of the video clips consisted of two dance performances which were presented side-by-side and were played simultaneously; one of a dancer in the happy condition and one of the same individual in the sad condition. After every film clip, the observers were asked to make forced-choices concerning the emotional state of the dancer. Results revealed that observers were able to identify the emotional state of the dancers with a high degree of accuracy. Moreover, emotions were more often recognized for female dancers than for their male counterparts. In addition, the results of eye tracking measurements unveiled that observers primarily focus on movements of the chest when decoding emotional information from dance movement. The findings of our study show that not merely portrayed emotions, but also induced emotions can be successfully recognized from free dance movement.

  3. Influence of the water content in protoplanetary discs on planet migration and formation

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Johansen, Anders

    2016-05-01

    The temperature and density profiles of protoplanetary discs depend crucially on the mass fraction of micrometre-sized dust grains and on their chemical composition. A larger abundance of micrometre-sized grains leads to an overall heating of the disc, so that the water ice line moves further away from the star. An increase in the water fraction inside the disc, maintaining a fixed dust abundance, increases the temperature in the icy regions of the disc and lowers the temperature in the inner regions. Discs with a larger silicate fraction have the opposite effect. Here we explore the consequence of the dust composition and abundance for the formation and migration of planets. We find that discs with low water content can only sustain outwards migration for planets up to 4 Earth masses, while outwards migration in discs with a larger water content persists up to 8 Earth masses in the late stages of the disc evolution. Icy planetary cores that do not reach run-away gas accretion can thus migrate to orbits close to the host star if the water abundance is low. Our results imply that hot and warm super-Earths found in exoplanet surveys could have formed beyond the ice line and thus contain a significant fraction in water. These water-rich super-Earths should orbit primarily around stars with a low oxygen abundance, where a low oxygen abundance is caused by either a low water-to-silicate ratio or by overall low metallicity.

  4. Sparse aperture masking interferometry survey of transitional discs. Search for substellar-mass companions and asymmetries in their parent discs

    NASA Astrophysics Data System (ADS)

    Willson, M.; Kraus, S.; Kluska, J.; Monnier, J. D.; Ireland, M.; Aarnio, A.; Sitko, M. L.; Calvet, N.; Espaillat, C.; Wilner, D. J.

    2016-10-01

    Context. Transitional discs are a class of circumstellar discs around young stars with extensive clearing of dusty material within their inner regions on 10s of au scales. One of the primary candidates for this kind of clearing is the formation of planet(s) within the disc that then accrete or clear their immediate area as they migrate through the disc. Aims: The goal of this survey was to search for asymmetries in the brightness distribution around a selection of transitional disc targets. We then aimed to determine whether these asymmetries trace dynamically-induced structures in the disc or the gap-opening planets themselves. Methods: Our sample included eight transitional discs. Using the Keck/NIRC2 instrument we utilised the Sparse Aperture Masking (SAM) interferometry technique to search for asymmetries indicative of ongoing planet formation. We searched for close-in companions using both model fitting and interferometric image reconstruction techniques. Using simulated data, we derived diagnostics that helped us to distinguish between point sources and extended asymmetric disc emission. In addition, we investigated the degeneracy between the contrast and separation that appear for marginally resolved companions. Results: We found FP Tau to contain a previously unseen disc wall, and DM Tau, LkHα330, and TW Hya to contain an asymmetric signal indicative of point source-like emission. We placed upper limits on the contrast of a companion in RXJ 1842.9-3532 and V2246 Oph. We ruled the asymmetry signal in RXJ 1615.3-3255 and V2062 Oph to be false positives. In the cases where our data indicated a potential companion we computed estimates for the value of McṀc and found values in the range of . Conclusions: We found significant asymmetries in four targets. Of these, three were consistent with companions. We resolved a previously unseen gap in the disc of FP Tau extending inwards from approximately 10 au. Based on observations made with the Keck observatory

  5. Seeing to the Event Horizon: Probing Accretion Physics with X-ray Reflection

    NASA Astrophysics Data System (ADS)

    Wilkins, Dan

    2015-09-01

    Accretion onto supermassive black holes in active galactic nuclei is known to power some of the most luminous objects we see in the Universe, which through their vast energy outputs must have played an important role in shaping the large scale structure of the Universe we see today. Much remains unknown, however, about the fine details of this process; exactly how energy is liberated from accretion flows onto black holes, how the 'corona' that produces the intense X-ray continuum is formed and what governs this process over time. I will outline how the detection of X-rays reflected from the discs of accreting material around black holes by the present generation of large X-ray observatories, shifted in energy and blurred by relativistic effects in the strong gravitational field close to the black hole, has enabled measurements of the inner regions of the accretion flow in unprecedented detail. In particular, exploiting the shift in energy of atomic emission lines by relativistic effects as a function of location on the disc has enabled the measurement of the illumination pattern of the accretion flow by the X-ray continuum from which the geometry of the emitting region can be inferred and how the detection of time lags between the primary and reflected X-rays owing to the additional path the reflected rays must travel between the corona and the disc places further constraints on the nature of the emitting corona. These techniques allow the evolution of the corona that accompanies transitions from high to low X-ray flux to be studied, giving clues to the physical process that forms and powers the intense X-ray source and uncovering evidence for the potential launching of jets. I will discuss the great steps forward in understanding accretion physics that can be made with the Athena X-ray observatory, combining detailed analysis of observations with predictions and models from general relativistic ray tracing simulations. In particular, I will discuss how high

  6. 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.

  7. SAD5 Stereo Correlation Line-Striping in an FPGA

    NASA Technical Reports Server (NTRS)

    Villalpando, Carlos Y.; Morfopoulos, Arin C.

    2011-01-01

    High precision SAD5 stereo computations can be performed in an FPGA (field-programmable gate array) at much higher speeds than possible in a conventional CPU (central processing unit), but this uses large amounts of FPGA resources that scale with image size. Of the two key resources in an FPGA, Slices and BRAM (block RAM), Slices scale linearly in the new algorithm with image size, and BRAM scales quadratically with image size. An approach was developed to trade latency for BRAM by sub-windowing the image vertically into overlapping strips and stitching the outputs together to create a single continuous disparity output. In stereo, the general rule of thumb is that the disparity search range must be 1/10 the image size. In the new algorithm, BRAM usage scales linearly with disparity search range and scales again linearly with line width. So a doubling of image size, say from 640 to 1,280, would in the previous design be an effective 4 of BRAM usage: 2 for line width, 2 again for disparity search range. The minimum strip size is twice the search range, and will produce an output strip width equal to the disparity search range. So assuming a disparity search range of 1/10 image width, 10 sequential runs of the minimum strip size would produce a full output image. This approach allowed the innovators to fit 1280 960 wide SAD5 stereo disparity in less than 80 BRAM, 52k Slices on a Virtex 5LX330T, 25% and 24% of resources, respectively. Using a 100-MHz clock, this build would perform stereo at 39 Hz. Of particular interest to JPL is that there is a flight qualified version of the Virtex 5: this could produce stereo results even for very large image sizes at 3 orders of magnitude faster than could be computed on the PowerPC 750 flight computer. The work covered in the report allows the stereo algorithm to run on much larger images than before, and using much less BRAM. This opens up choices for a smaller flight FPGA (which saves power and space), or for other algorithms

  8. 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.

  9. Mechanotransduction in intervertebral discs

    PubMed Central

    Tsai, Tsung-Ting; Cheng, Chao-Min; Chen, Chien-Fu; Lai, Po-Liang

    2014-01-01

    Mechanotransduction plays a critical role in intracellular functioning—it allows cells to translate external physical forces into internal biochemical activities, thereby affecting processes ranging from proliferation and apoptosis to gene expression and protein synthesis in a complex web of interactions and reactions. Accordingly, aberrant mechanotransduction can either lead to, or be a result of, a variety of diseases or degenerative states. In this review, we provide an overview of mechanotransduction in the context of intervertebral discs, with a focus on the latest methods of investigating mechanotransduction and the most recent findings regarding the means and effects of mechanotransduction in healthy and degenerative discs. We also provide some discussion of potential directions for future research and treatments. PMID:25267492

  10. Biomechanics of Disc Degeneration

    PubMed Central

    Palepu, V.; Kodigudla, M.; Goel, V. K.

    2012-01-01

    Disc degeneration and associated disorders are among the most debated topics in the orthopedic literature over the past few decades. These may be attributed to interrelated mechanical, biochemical, and environmental factors. The treatment options vary from conservative approaches to surgery, depending on the severity of degeneration and response to conservative therapies. Spinal fusion is considered to be the “gold standard” in surgical methods till date. However, the association of adjacent level degeneration has led to the evolution of motion preservation technologies like spinal arthroplasty and posterior dynamic stabilization systems. These new technologies are aimed to address pain and preserve motion while maintaining a proper load sharing among various spinal elements. This paper provides an elaborative biomechanical review of the technologies aimed to address the disc degeneration and reiterates the point that biomechanical efficacy followed by long-term clinical success will allow these nonfusion technologies as alternatives to fusion, at least in certain patient population. PMID:22745914

  11. LUMBAR DISC HERNIATION

    PubMed Central

    Vialle, Luis Roberto; Vialle, Emiliano Neves; Suárez Henao, Juan Esteban; Giraldo, Gustavo

    2015-01-01

    Lumbar disc herniation is the most common diagnosis among the degenerative abnormalities of the lumbar spine (affecting 2 to 3% of the population), and is the principal cause of spinal surgery among the adult population. The typical clinical picture includes initial lumbalgia, followed by progressive sciatica. The natural history of disc herniation is one of rapid resolution of the symptoms (four to six weeks). The initial treatment should be conservative, managed through medication and physiotherapy, sometimes associated with percutaneous nerve root block. Surgical treatment is indicated if pain control is unsuccessful, if there is a motor deficit greater than grade 3, if there is radicular pain associated with foraminal stenosis, or if cauda equina syndrome is present. The latter represents a medical emergency. A refined surgical technique, with removal of the extruded fragment and preservation of the ligamentum flavum, resolves the sciatic symptoms and reduces the risk of recurrence over the long term. PMID:27019834

  12. [Cervical disc herniation].

    PubMed

    Schnake, K J; Hoffmann, C-H; Kandziora, F

    2012-12-01

    The cervical disc herniation is characterized by prolapsed nucleus pulposus material through the annulus into the spinal canal. The local mechanical or chemical irritation of neural structures typically leads to symptoms of radiculopathy, cervicocephalgia or myelopathy. Pronounced sensorimotor deficits or intractable pain constitute surgical treatment. In all other cases conservative treatment is indicated, including pain medication, active and passive physiotherapy, and local injections, respectively. Anterior cervical discectomy and interbody fusion (ACDF) is still the surgical treatment of choice. Predominantly, cages with or without plates are in use to obtain solid fusion. The implantation of a total disc replacement is a viable alternative, if no contraindications exist. Other surgical techniques may be performed in proper selected cases. The overall clinical and radiological results of both surgical and conservative treatment are good. PMID:23296562

  13. Evolution of binary black holes in self gravitating discs. Dissecting the torques

    NASA Astrophysics Data System (ADS)

    Roedig, C.; Sesana, A.; Dotti, M.; Cuadra, J.; Amaro-Seoane, P.; Haardt, F.

    2012-09-01

    Context. Massive black hole binaries, formed in galaxy mergers, are expected to evolve in dense circumbinary discs. Understanding of the disc-binary coupled dynamics is vital to assess both the final fate of the system and its potentially observable features. Aims: Aimed at understanding the physical roots of the secular evolution of the binary, we study the interplay between gas accretion and gravity torques in changing the binary elements (semi-major axis and eccentricity) and its total angular momentum budget. We pay special attention to the gravity torques, by analysing their physical origin and location within the disc. Methods: We analysed three-dimensional smoothed particle hydrodynamics simulations of the evolution of initially quasi-circular massive black hole binaries (BHBs) residing in the central hollow (cavity) of massive self-gravitating circumbinary discs. We performed a set of simulations adopting different thermodynamics for the gas within the cavity and for the "numerical size" of the black holes. Results: We show that (i) the BHB eccentricity growth found in our previous work is a general result, independent of the accretion and the adopted thermodynamics; (ii) the semi-major axis decay depends not only on the gravity torques but also on their subtle interplay with the disc-binary angular momentum transfer due to accretion; (iii) the spectral structure of the gravity torques is predominately caused by disc edge overdensities and spiral arms developing in the body of the disc and, in general, does not reflect directly the period of the binary; (iv) the net gravity torque changes sign across the BHB corotation radius (positive inside vs negative outside) We quantify the relative importance of the two, which appear to depend on the thermodynamical properties of the instreaming gas, and which is crucial in assessing the disc-binary angular momentum transfer; (v) the net torque manifests as a purely kinematic (non-resonant) effect as it stems from the

  14. He-accreting white dwarfs: accretion regimes and final outcomes

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The behaviour of carbon-oxygen (CO) white dwarfs (WDs) subject to direct helium accretion is extensively studied. We aim to analyse the thermal response of an accreting WD to mass deposition at different timescales. The analysis has been performed for initial WD masses and accretion rates in the range 0.60-1.02 M⊙ and 10-9-10-5 M⊙ yr-1, respectively. Thermal regimes in the parameter space MWD-dot{M}_He leading to formation of red-giant-like structures, steady burning of He, and mild, strong and dynamical flashes have been identified and the transition between these regimes has been studied in detail. In particular, the physical properties of WDs experiencing the He-flash accretion regime have been investigated to determine the mass retention efficiency as a function of the accretor total mass and accretion rate. We also discuss to what extent the building up of a He-rich layer via H burning could be described according to the behaviour of models accreting He-rich matter directly. Polynomial fits to the obtained results are provided for use in binary population synthesis computations. Several applications for close binary systems with He-rich donors and CO WD accretors are considered and the relevance of the results for interpreting He novae is discussed.

  15. Total disc replacement.

    PubMed

    Vital, J-M; Boissière, L

    2014-02-01

    Total disc replacement (TDR) (partial disc replacement will not be described) has been used in the lumbar spine since the 1980s, and more recently in the cervical spine. Although the biomechanical concepts are the same and both are inserted through an anterior approach, lumbar TDR is conventionally indicated for chronic low back pain, whereas cervical TDR is used for soft discal hernia resulting in cervicobrachial neuralgia. The insertion technique must be rigorous, with precise centering in the disc space, taking account of vascular anatomy, which is more complex in the lumbar region, particularly proximally to L5-S1. All of the numerous studies, including prospective randomized comparative trials, have demonstrated non-inferiority to fusion, or even short-term superiority regarding speed of improvement. The main implant-related complication is bridging heterotopic ossification with resulting loss of range of motion and increased rates of adjacent segment degeneration, although with an incidence lower than after arthrodesis. A sufficiently long follow-up, which has not yet been reached, will be necessary to establish definitively an advantage for TDR, particularly in the cervical spine. PMID:24412045

  16. Agitating mass transfer with a warped disc's shadow

    NASA Astrophysics Data System (ADS)

    Cambier, H.

    2015-10-01

    For compact objects fed by Roche lobe overflow, accretion-generated X-rays irradiating the donor star can alter gas flow towards the Lagrange point thus varying mass transfer. The latest work specific to this topic consists of simple yet insightful two-dimensional hydrodynamics simulations stressing the role of global flow. To explore how a time-varying disc shadow affects mass transfer, I generalize the geometry, employ a robust hydrodynamics solver, and use phase space analysis near the nozzle to include coriolis lift there. Without even exposing the nozzle, a warped disc's shadow can drive mass transfer cycles by shifting the equatorial edges of the irradiation patches in turns: drawing in denser ambient gas before sweeping it into the nozzle. Other important effects remain missing in two-dimensional models, which I discuss along with prospects for more detailed yet efficient models.

  17. James Clerk Maxwell and the dynamics of astrophysical discs.

    PubMed

    Ogilvie, Gordon I

    2008-05-28

    Maxwell's investigations into the stability of Saturn's rings provide one of the earliest analyses of the dynamics of astrophysical discs. Current research in planetary rings extends Maxwell's kinetic theory to treat dense granular gases of particles undergoing moderately frequent inelastic collisions. Rather than disrupting the rings, local instabilities may be responsible for generating their irregular radial structure. Accretion discs around black holes or compact stars consist of a plasma permeated by a tangled magnetic field and may be compared with laboratory fluids through an analogy that connects Maxwell's researches in electromagnetism and viscoelasticity. A common theme in this work is the appearance of a complex fluid with a dynamical constitutive equation relating the stress in the medium to the history of its deformation.

  18. Does sadness impair color perception? Flawed evidence and faulty methods

    PubMed Central

    Holcombe, Alex O.; Brown, Nicholas J. L.; Goodbourn, Patrick T.; Etz, Alexander; Geukes, Sebastian

    2016-01-01

    In their 2015 paper, Thorstenson, Pazda, and Elliot offered evidence from two experiments that perception of colors on the blue–yellow axis was impaired if the participants had watched a sad movie clip, compared to participants who watched clips designed to induce a happy or neutral mood. Subsequently, these authors retracted their article, citing a mistake in their statistical analyses and a problem with the data in one of their experiments. Here, we discuss a number of other methodological problems with Thorstenson et al.’s experimental design, and also demonstrate that the problems with the data go beyond what these authors reported. We conclude that repeating one of the two experiments, with the minor revisions proposed by Thorstenson et al., will not be sufficient to address the problems with this work.

  19. Pupillary contagion: central mechanisms engaged in sadness processing

    PubMed Central

    Harrison, Neil A.; Singer, Tania; Rotshtein, Pia; Dolan, Ray J.; Critchley, Hugo D.

    2006-01-01

    Empathic responses underlie our ability to share emotions and sensations with others. We investigated whether observed pupil size modulates our perception of other's emotional expressions and examined the central mechanisms modulated by incidental perception of pupil size in emotional facial expressions. We show that diminishing pupil size enhances ratings of emotional intensity and valence for sad, but not happy, angry or neutral facial expressions. This effect was associated with modulation of neural activity within cortical and subcortical regions implicated in social cognition. In an identical context, we show that the observed pupil size was mirrored by the observers’ own pupil size. This empathetic contagion engaged the brainstem pupillary control nuclei (Edinger–Westphal) in proportion to individual subject's sensitivity to this effect. These findings provide evidence that perception–action mechanisms extend to non-volitional operations of the autonomic nervous system. PMID:17186063

  20. Does sadness impair color perception? Flawed evidence and faulty methods.

    PubMed

    Holcombe, Alex O; Brown, Nicholas J L; Goodbourn, Patrick T; Etz, Alexander; Geukes, Sebastian

    2016-01-01

    In their 2015 paper, Thorstenson, Pazda, and Elliot offered evidence from two experiments that perception of colors on the blue-yellow axis was impaired if the participants had watched a sad movie clip, compared to participants who watched clips designed to induce a happy or neutral mood. Subsequently, these authors retracted their article, citing a mistake in their statistical analyses and a problem with the data in one of their experiments. Here, we discuss a number of other methodological problems with Thorstenson et al.'s experimental design, and also demonstrate that the problems with the data go beyond what these authors reported. We conclude that repeating one of the two experiments, with the minor revisions proposed by Thorstenson et al., will not be sufficient to address the problems with this work. PMID:27606051

  1. Does sadness impair color perception? Flawed evidence and faulty methods

    PubMed Central

    Holcombe, Alex O.; Brown, Nicholas J. L.; Goodbourn, Patrick T.; Etz, Alexander; Geukes, Sebastian

    2016-01-01

    In their 2015 paper, Thorstenson, Pazda, and Elliot offered evidence from two experiments that perception of colors on the blue–yellow axis was impaired if the participants had watched a sad movie clip, compared to participants who watched clips designed to induce a happy or neutral mood. Subsequently, these authors retracted their article, citing a mistake in their statistical analyses and a problem with the data in one of their experiments. Here, we discuss a number of other methodological problems with Thorstenson et al.’s experimental design, and also demonstrate that the problems with the data go beyond what these authors reported. We conclude that repeating one of the two experiments, with the minor revisions proposed by Thorstenson et al., will not be sufficient to address the problems with this work. PMID:27606051

  2. Medical Physics Education at the University of Novi Sad - Serbia

    NASA Astrophysics Data System (ADS)

    Stanković, Slobodanka; Vesković, Miroslav; Klisurić, Olivera; Spasić, Vesna

    2007-04-01

    Overview of new educational program and training in Medical Physics at the University of Novi Sad is presented, where the medical physics education from undergraduate to doctoral study is established in the last decade. Necessity for basic and additional education and hospital training for medical physicists becomes the evident subject in clinical practice in which physicists and physicians are in close collaboration to ensure high quality of patient care. Learning objectives: to incorporate the latest scientific and professional findings in the field of medical physics, medical diagnostics, therapy and instruments; to accomodate students' pursuits of individual fields by offering elective courses from different areas of current medical practice; to reflect the multidisciplinary spirit of the studies, since teaching is performed by experts from diverse fields.

  3. A Semi-Analytic Study of Feedback Processes and Metallicity Profiles in Disc Galaxies

    NASA Astrophysics Data System (ADS)

    Sandford, Nathan Ross; Lu, Yu

    2016-01-01

    The metallicity gradients of disc galaxies contain valuable information about the physics governing their formation and evolution. The observed metallicity profiles have negative gradients that are steeper at high redshifts, indicating an inside-out formation of disc galaxies. We improve on our semi-analytic galaxy formation model (Lu, Mo & Wechsler 2015) by incorporating the radial distribution of metals into the model. With the improved model, we explore how feedback scenarios affect metallicity gradients. The model features 3 feedback scenarios: An Ejective (EJ) model, which includes ejective supernova (SN) feedback, a PRe-Heating (PR) model, which assumes that the intergalactic medium is preheated, preventing it from collapsing onto galaxies, and a Re-Incorporation (RI) model, which also includes strong outflows but allows ejected gas to re-accrete onto the galaxies. We compare the models with observations from Ho et al. (2015) and find that while all models struggle to match the observed metallicity gradient-stellar mass relationship, the PR model predicts metallicity gradients that best match observations. We also find that the RI model predicts a flat gradient because its outflow and re-accretion replenish the disc uniformly with newly accreted enriched gas, erasing the mark of inside-out formation. Our findings suggest feedback plays a key role in shaping the metallicity gradients of disc galaxies and require more detailed theoretical modeling to understand them.

  4. 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.

  5. On the interaction between sad mood and cognitive control: the effect of induced sadness on electrophysiological modulations underlying Stroop conflict processing.

    PubMed

    Nixon, Elena; Liddle, Peter F; Nixon, Neil L; Liotti, Mario

    2013-03-01

    The present study employed high-density ERPs to examine the effect of induced sad mood on the spatiotemporal correlates of conflict monitoring and resolution in a colour-word Stroop interference task. Neuroimaging evidence and dipole modelling implicates the involvement of the anterior cingulate cortex (ACC) and medial prefrontal cortex (mPFC) regions in conflict-laden interference control. On the basis that these structures have been found to mediate emotion-cognition interactions in negative mood states, it was predicted that Stroop-related cognitive control, which relies heavily on anterior neural sources, would be affected by effective sad mood provocation. Healthy participants (N=14) were induced into transient sadness via use of autobiographical sad scripts, a well-validated mood induction technique (Liotti et al., 2000a, 2002). In accord with previous research, interference effects were shown at both baseline and sad states while Stroop conflict was associated with early (N450) and late (Late Positive Component; LPC) electrophysiological modulations at both states. Sad mood induction attenuated the N450 effect in line with our expectation that it would be susceptible to modulation by mood, given its purported anterior limbic source. The LPC effect was displayed at the typical posterior lateral sites but, as predicted, was not affected by sad mood. However, frontocentral LPC activity-presumably generated from an additional anterior limbic source-was affected at sad state, hinting a role in conflict monitoring. Although the neurophysiological underpinnings of interference control are yet to be clarified, this study provided further insight into emotion-cognition interactions as indexed by Stroop conflict-laden processing.

  6. Chemodynamical analysis of bulge stars for simulated disc galaxies

    NASA Astrophysics Data System (ADS)

    Rahimi, A.; Kawata, D.; Brook, Chris B.; Gibson, Brad K.

    2010-01-01

    We analyse the kinematics and chemistry of the bulge stars of two simulated disc galaxies using our chemodynamical galaxy evolution code GCD+. First, we compare stars that are born inside the galaxy with those that are born outside the galaxy and are accreted into the centre of the galaxy. Stars that originate outside the bulge are accreted into it early in its formation within 3 Gyr so that these stars have high [α/Fe] as well as a high total energy reflecting their accretion to the centre of the galaxy. Therefore, higher total energy is a good indicator for finding accreted stars. The bulges of the simulated galaxies formed through multiple mergers separated by about a Gyr. Since [α/Fe] is sensitive to the first few Gyr of star formation history, stars that formed during mergers at different epochs show different [α/Fe]. We show that the [Mg/Fe] against star formation time relation can be very useful to identify a multiple merger bulge formation scenario, provided there is sufficiently good age information available. Our simulations also show that stars formed during one of the merger events retain a systematically prograde rotation at the final time. This demonstrates that the orbit of the ancient merger that helped to form the bulge could still remain in the kinematics of bulge stars.

  7. Planetary system formation in thermally evolving viscous protoplanetary discs.

    PubMed

    Nelson, Richard P; Hellary, Phil; Fendyke, Stephen M; Coleman, Gavin

    2014-04-28

    Observations of extrasolar planets are providing new opportunities for furthering our understanding of planetary formation processes. In this paper, we review planet formation and migration scenarios and describe some recent simulations that combine planetary accretion and gas-disc-driven migration. While the simulations are successful at forming populations of low- and intermediate-mass planets with short orbital periods, similar to those that are being observed by ground- and space-based surveys, our models fail to form any gas giant planets that survive migration into the central star. The simulation results are contrasted with observations, and areas of future model development are discussed.

  8. Planetary system formation in thermally evolving viscous protoplanetary discs.

    PubMed

    Nelson, Richard P; Hellary, Phil; Fendyke, Stephen M; Coleman, Gavin

    2014-04-28

    Observations of extrasolar planets are providing new opportunities for furthering our understanding of planetary formation processes. In this paper, we review planet formation and migration scenarios and describe some recent simulations that combine planetary accretion and gas-disc-driven migration. While the simulations are successful at forming populations of low- and intermediate-mass planets with short orbital periods, similar to those that are being observed by ground- and space-based surveys, our models fail to form any gas giant planets that survive migration into the central star. The simulation results are contrasted with observations, and areas of future model development are discussed. PMID:24664913

  9. Analytical calculations of the radial structure of self-gravitating and magnetized accretion disks in AGN.

    NASA Astrophysics Data System (ADS)

    Lu, Y.; Yang, L.; Wu, S.

    1997-11-01

    The variation with radius of the physical parameters(scale height, central temperature, and central density) of a self-gravitation and magnetized accretion disk is examined.We have adopted the different opacities in different regions as in the work by Collin-Souffrin and Dumont (1990A&A...229..292C), and we consider a disc model with a 10^7^Msun_ black hole at the center and with an accretion rate of 0.01Msun_/yr. Most of our results are very similar to theirs, but there are some differences between ours and theirs, that is: the critical radius where X-rays are able to heat significantly the disc is not sensitive to self-gravitation. However, self-gravitation has an influence on the location of the radius which emits the bulk of UV radiation, and the magnetic field affects both of them.

  10. Single neutron star systems evolving with fallback discs

    NASA Astrophysics Data System (ADS)

    Ertan, Unal; Caliskan, Sirin; Alpar, Mehmet Ali; Benli, Onur; Trümper, Joachim E.

    2016-07-01

    We have investigated the long-term evolution of the young neutron star systems, namely anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), dim isolated neutron stars (XDINs), and the so-called "high-B radio pulsars" in the frame of the fallback disk disc model. We have shown that the X-ray luminosities and the rotational properties of individual sources in these different populations can be achieved by neutron stars evolving with fallback disks and with conventional dipole magnetic fields of young neutron stars. Presence of small-scale magnetar fields in the higher multi-poles which are likely to be responsible for soft gamma bursts observed from these systems is compatible with the fallback disk model, since the rotational evolution of the star is governed by the interaction between the large-scale dipole field and the disc. The results of our model is self-consistent in that (1) the X-ray luminosity, period and period derivative of individual sources are produced simultaneously, and (2) these results are obtained with very similar set of main disk parameters for all these systems with rather different properties. Our results indicate that all known AXPs, except two sources, are in the accretion phase at present. The 6 XDINs with confirmed period and period derivatives reached their long periods in the accretion epochs in the past. At present, XDINs are evolving in the propeller phase without accretion, but they are still slowing down under effect of the disk torques. For the "high-B radio pulsars", the source properties are obtained in the phases when accretion is not allowed, which is consistent with the radio pulsar property of these sources.

  11. 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.

  12. Disc edge veins of Kraupa associated with optic disc drusen

    PubMed Central

    Díaz, Andrea; Almela, Miguel Angel

    2014-01-01

    Objective: Disc edge veins of Kraupa are a rare anomaly of the retinal venous system in which the main trunk of the retinal vein disappeared into the margin of the optic disc instead of its centre. Methods: A 40-year-old woman was detected to have an anomaly in her left optic disc in a routine eye examination. The eyes had an anomaly of the retinal venous system in which all branches of the retinal vein joined in a common trunk that entered the disc margin inferonasally. The central retinal artery issued from the centre of the disc separately of the venous system. B-scan ultrasonografhy revealed the presence of hyperechoic imaging at the optic nerve head in both eyes. Results: We describe the association of disc edge veins of Kraupa with optic disc drusen. Conclusion: Vascular complications of optic disc drusen hav been described. We don’t know the implication of disc edge veins in the pathogenesis of these complications.

  13. The Sad, the Angry, and the Asymmetrical Brain: Dichotic Listening Studies of Negative Affect and Depression

    ERIC Educational Resources Information Center

    Gadea, Marien; Espert, Raul; Salvador, Alicia; Marti-Bonmati, Luis

    2011-01-01

    Dichotic Listening (DL) is a valuable tool to study emotional brain lateralization. Regarding the perception of sadness and anger through affective prosody, the main finding has been a left ear advantage (LEA) for the sad but contradictory data for the anger prosody. Regarding an induced mood in the laboratory, its consequences upon DL were a…

  14. Anger and Sadness Perception in Clinically Referred Preschoolers: Emotion Processes and Externalizing Behavior Symptoms

    ERIC Educational Resources Information Center

    Martin, Sarah E.; Boekamp, John R.; McConville, David W.; Wheeler, Elizabeth E.

    2010-01-01

    This study examined emotion perception processes in preschool aged children presenting with clinically significant emotional and behavior problems, with emphasis on sadness perception accuracy (i.e., the ability to correctly identify sadness from expressive and situational cues) and anger perception bias (i.e., the tendency to perceive anger in…

  15. Parental Socialization of Sadness Regulation in Middle Childhood: The Role of Expectations and Gender

    ERIC Educational Resources Information Center

    Cassano, Michael C.; Zeman, Janice L.

    2010-01-01

    The authors of this study investigated mothers' and fathers' socialization of their children's sadness. The particular focus was an examination of how socialization practices changed when parents' expectancies concerning their child's sadness management abilities were violated. Methods included an experimental manipulation and direct observation…

  16. Disc formation in turbulent cloud cores: is magnetic flux loss necessary to stop the magnetic braking catastrophe or not?

    NASA Astrophysics Data System (ADS)

    Santos-Lima, R.; de Gouveia Dal Pino, E. M.; Lazarian, A.

    2013-03-01

    Recent numerical analysis of Keplerian disc formation in turbulent, magnetized cloud cores by Santos-Lima et al. demonstrated that reconnection diffusion is an efficient process to remove the magnetic flux excess during the buildup of a rotationally supported disc. This process is induced by fast reconnection of the magnetic fields in a turbulent flow. In a similar numerical study, Seifried et al. concluded that reconnection diffusion or any other non-ideal magnetohydrodynamic effects would not be necessary and turbulence shear alone would provide a natural way to build up a rotating disc without requiring magnetic flux loss. Their conclusion was based on the fact that the mean mass-to-flux ratio (μ) evaluated over a spherical region with a radius much larger than the disc is nearly constant in their models. In this paper, we compare the two sets of simulations and show that this averaging over large scales can mask significant real increases of μ in the inner regions where the disc is built up. We demonstrate that turbulence-induced reconnection diffusion of the magnetic field happens in the initial stages of the disc formation in the turbulent envelope material that is accreting. Our analysis is suggestive that reconnection diffusion is present in both sets of simulations and provides a simple solution for the `magnetic braking catastrophe' which is discussed in the literature in relation to the formation of protostellar accretion discs.

  17. Heat distribution in disc brake

    NASA Astrophysics Data System (ADS)

    Klimenda, Frantisek; Soukup, Josef; Kampo, Jan

    2016-06-01

    This article is deals by the thermal analysis of the disc brake with floating caliper. The issue is solved by numerically. The half 2D model is used for solution in program ADINA 8.8. Two brake discs without the ventilation are solved. One disc is made from cast iron and the second is made from stainless steel. Both materials are an isotropic. By acting the pressure force on the brake pads will be pressing the pads to the brake disc. Speed will be reduced (slowing down). On the contact surface generates the heat, which the disc and pads heats. In the next part of article is comparison the maximum temperature at the time of braking. The temperatures of both materials for brake disc (gray cast iron, stainless steel) are compares. The heat flux during braking for the both materials is shown.

  18. Edge-on thick discs

    NASA Astrophysics Data System (ADS)

    Kasparova, A.; Katkov, I.; Chilingarian, I.; Silchenko, O.; Moiseev, A.; Borisov, S.

    2016-06-01

    Although thick stellar discs are detected in nearly all edge-on disc galaxies, their formation scenarios still remain a matter of debate. Due to observational difficulties, there is a lack of information about their stellar populations. Using the Russian 6-m telescope BTA we collected deep spectra of thick discs in three edge-on early-type disc galaxies located in different environments: NGC4111 in a dense group, NGC4710 in the Virgo cluster, and NGC5422 in a sparse group. We see intermediate age (4 ‑ 5 Gyr) metal rich ([Fe/H] ~ ‑0.2 ‑ 0.0 dex) stellar populations in NGC4111 and NGC4710. On the other hand, NGC5422 does not harbour young stars, its only disc is thick and old (10 Gyr) and its α-element abundance suggests a long formation epoch implying its formation at high redshift. Our results prove the diversity of thick disc formation scenarios.

  19. Enclosed rotary disc air pulser

    DOEpatents

    Olson, A. L.; Batcheller, Tom A.; Rindfleisch, J. A.; Morgan, John M.

    1989-01-01

    An enclosed rotary disc air pulser for use with a solvent extraction pulse olumn includes a housing having inlet, exhaust and pulse leg ports, a shaft mounted in the housing and adapted for axial rotation therein, first and second disc members secured to the shaft within the housing in spaced relation to each other to define a chamber therebetween, the chamber being in communication with the pulse leg port, the first disc member located adjacent the inlet port, the second disc member being located adjacent the exhaust port, each disc member having a milled out portion, the disc members positioned on the shaft so that as the shaft rotates, the milled out portions permit alternative cyclical communication between the inlet port and the chamber and the exhaust port and the chamber.

  20. Effects of sad mood on facial emotion recognition in Chinese people.

    PubMed

    Lee, Tatia M C; Ng, Emily H H; Tang, S W; Chan, Chetwyn C H

    2008-05-30

    This study examined the influence of sad mood on the judgment of ambiguous facial emotion expressions among 47 healthy volunteers who had been induced to feel sad (n=13), neutral (n=15), or happy (n=19) emotions by watching video clips. The findings suggest that when the targets were ambiguous, participants who were in a sad mood tended to classify them in the negative emotional categories rather than the positive emotional categories. Also, this observation indicates that emotion-specific negative bias in the judgment of facial expressions is associated with a sad mood. The finding argues against a general impairment in decoding facial expressions. Furthermore, the observed mood-congruent negative bias was best predicted by spatial perception. The findings of this study provide insights into the cognitive processes underlying the interpersonal difficulties experienced by people in a sad mood, which may be predisposing factors in the development of clinical depression.

  1. Structural insight into the mechanism of synergistic autoinhibition of SAD kinases

    PubMed Central

    Wu, Jing-Xiang; Cheng, Yun-Sheng; Wang, Jue; Chen, Lei; Ding, Mei; Wu, Jia-Wei

    2015-01-01

    The SAD/BRSK kinases participate in various important life processes, including neural development, cell cycle and energy metabolism. Like other members of the AMPK family, SAD contains an N-terminal kinase domain followed by the characteristic UBA and KA1 domains. Here we identify a unique autoinhibitory sequence (AIS) in SAD kinases, which exerts autoregulation in cooperation with UBA. Structural studies of mouse SAD-A revealed that UBA binds to the kinase domain in a distinct mode and, more importantly, AIS nestles specifically into the KD-UBA junction. The cooperative action of AIS and UBA results in an ‘αC-out' inactive kinase, which is conserved across species and essential for presynaptic vesicle clustering in C. elegans. In addition, the AIS, along with the KA1 domain, is indispensable for phospholipid binding. Taken together, these data suggest a model for synergistic autoinhibition and membrane activation of SAD kinases. PMID:26626945

  2. Attentional Biases and the Persistence of Sad Mood in Major Depressive Disorder

    PubMed Central

    Clasen, Peter C.; Wells, Tony T.; Ellis, Alissa J.; Beevers, Christopher G.

    2013-01-01

    This study examined whether attentional biases for emotional information are associated with impaired mood recovery following a sad mood induction among individuals with and without major depressive disorder (MDD). Attentional biases were assessed with an exogenous cuing task using emotional facial expressions as cues among adults with (n = 48) and without (n = 224) current MDD. Mood reactivity and recovery were measured following a sad mood induction. Mood reactivity strongly predicted mood recovery; however, this relationship was moderated by attentional biases for negative emotional stimuli. Biases for sad and fear stimuli were associated with diminished mood recovery following mood induction across the sample. However, biases for sad stimuli were associated with significantly greater impairments in mood recovery among individuals with MDD than healthy controls. Furthermore, within the MDD group, impaired mood recovery was positively associated with depression severity. These results suggest that attentional biases maintain depression, in part, by facilitating the persistence of sad mood. PMID:22867117

  3. The binary millisecond pulsar PSR J1023+0038 during its accretion state - I. Optical variability

    NASA Astrophysics Data System (ADS)

    Shahbaz, T.; Linares, M.; Nevado, S. P.; Rodríguez-Gil, P.; Casares, J.; Dhillon, V. S.; Marsh, T. R.; Littlefair, S.; Leckngam, A.; Poshyachinda, S.

    2015-11-01

    We present time-resolved optical photometry of the binary millisecond `redback' pulsar PSR J1023+0038 (=AY Sex) during its low-mass X-ray binary phase. The light curves taken between 2014 January and April show an underlying sinusoidal modulation due to the irradiated secondary star and accretion disc. We also observe superimposed rapid flaring on time-scales as short as ˜20 s with amplitudes of ˜0.1-0.5 mag and additional large flare events on time-scales of ˜5-60 min with amplitudes of ˜0.5-1.0 mag. The power density spectrum of the optical flare light curves is dominated by a red-noise component, typical of aperiodic activity in X-ray binaries. Simultaneous X-ray and UV observations by the Swift satellite reveal strong correlations that are consistent with X-ray reprocessing of the UV light, most likely in the outer regions of the accretion disc. On some nights we also observe sharp-edged, rectangular, flat-bottomed dips randomly distributed in orbital phase, with a median duration of ˜250 s and a median ingress/egress time of ˜20 s. These rectangular dips are similar to the mode-switching behaviour between disc `active' and `passive' luminosity states, observed in the X-ray light curves of other redback millisecond pulsars. This is the first time that the optical analogue of the X-ray mode-switching has been observed. The properties of the passive- and active-state light curves can be explained in terms of clumpy accretion from a trapped inner accretion disc near the corotation radius, resulting in rectangular, flat-bottomed optical and X-ray light curves.

  4. Revealing accretion onto black holes through X-ray reflection

    NASA Astrophysics Data System (ADS)

    Plant, D.; Fender, R.; Ponti, G.; Munoz-Darias, T.; Coriat, M.

    2014-07-01

    Understanding the dynamics behind black hole state transitions and the changes they reflect in outbursts has become long-standing problem. The X-ray reflection spectrum describes the interaction between the hard X-ray source (the power-law continuum) and the cool accretion disc it illuminates, and thus permits an indirect view of how the two evolve. We present a systematic analysis of the reflection spectrum throughout three outbursts (500+ RXTE observations) of the black hole binary GX 339-4, representing the largest study applying a self-consistent treatment of reflection to date. Particular attention is payed to the coincident evolution of the power-law and reflection, which can be used to determine the accretion geometry. The hard state is found to be distinctly reflection weak, however the ratio of reflection to power-law gradually increases as the source luminosity rises. In contrast the reflection is found dominate the power-law throughout most of the soft state, with increasing supremacy as the source decays. Using results from archival and AO-12 observations of GX 339-4 with XMM-Newton we reveal the dynamics driving this evolution and the nature of accretion onto black holes in outburst.

  5. Thin accretion disks in f(R) modified gravity models

    SciTech Connect

    Pun, C. S. J.; Harko, T.; Kovacs, Z.

    2008-07-15

    We consider 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. The Lagrangian of the generalized gravity theory is also obtained in a parametric form, and the conditions of the viability of the model are also discussed. The exact Schwarzschild-type solution of the gravitational field equations in the f(R) gravity contains a linearly increasing term, as well as a logarithmic correction, as compared to the standard Schwarzschild solution of general relativity, and it depends on four arbitrary integration constants. The energy flux and the emission spectrum from the accretion disk around the f(R) gravity black holes are obtained, and they are compared to the general relativistic case. Particular signatures can appear in the electromagnetic spectrum, thus leading to the possibility of directly testing modified gravity models by using astrophysical observations of the emission spectra from accretion disks.

  6. CsSAD: a fatty acid desaturase gene involved in abiotic resistance in Camellia sinensis (L.).

    PubMed

    Ding, Z T; Shen, J Z; Pan, L L; Wang, Y U; Li, Y S; Wang, Y; Sun, H W

    2016-01-01

    Tea (Camellia sinensis L.) is a thermophilic evergreen woody plant that has poor cold tolerance. The SAD gene plays a key role in regulating fatty acid synthesis and membrane lipid fluidity in response to temperature change. In this study, full-length SAD cDNA was cloned from tea leaves using rapid amplification of cDNA ends and polymerase chain reaction (PCR)-based methods. Sequence analysis demonstrated that CsSAD had a high similarity to other corresponding cDNAs. At 25°C, the CsSAD transcriptional level was highest in the leaf and lowest in the stem, but there was no obvious difference between the root and stem organs. CsSAD expression was investigated by reverse transcription-PCR, which showed that CsSAD was upregulated at 4° and -5°C. At 25°C, CsSAD was induced by polyethylene glycol, abscisic acid, and wounding, and a similar trend was observed at 4°C, but the mean expression level at 4°C was lower than that at 25°C. Under natural cold acclimation, the 'CsCr05' variety's CsSAD expression level increased before decreasing. The CsSAD expression level in variety 'CsCr06' showed no obvious change at first, but rapidly increased to a maximum when the temperature was very low. Our study demonstrates that CsSAD is upregulated in response to different abiotic conditions, and that it is important to study the stress resistance of the tea plant, particularly in response to low temperature, drought, and wounding. PMID:26985937

  7. Numbered nasal discs for waterfowl

    USGS Publications Warehouse

    Bartonek, J.C.; Dane, C.W.

    1964-01-01

    Numbered nasal discs were successfully used in studies requiring large numbers of individually marked waterfowl. The procedure for constructing these discs is outlined. Blue-winged teal (Anas discors) with 5/8-inch discs, and canvasback (Aythya valisineria) and redhead (A. americana) with 3/4-inch discs can be individually identified up to 50 and 80 yards, respectively, with a gunstock-mounted, 20-power spotting scope. The particular value of these markers is their durability, the number of combinations possible, and the apparent absence of behavioral or mortality influence among such species as the blue-winged teal.

  8. Mass accretion rates from multiband photometry in the Carina Nebula: the case of Trumpler 14

    NASA Astrophysics Data System (ADS)

    Beccari, G.; De Marchi, G.; Panagia, N.; Valenti, E.; Carraro, G.; Romaniello, M.; Zoccali, M.; Weidner, C.

    2015-01-01

    Context. We present a study of the mass accretion rates of pre-main sequence (PMS) stars in the cluster Trumpler 14 (Tr 14) in the Carina Nebula. Using optical multiband photometry we were able to identify 356 PMS stars showing Hα excess emission with equivalent width EW(Hα) > 20 Å. We interpret this observational feature as an indication that these objects are still actively accreting gas from their circumstellar medium. From a comparison of the HR diagram with PMS evolutionary models we derive ages and masses of the PMS stars. We find that most of the PMS objects are younger than 10 Myr with a median age of ~3 Myr. Surprisingly, we also find that ~20% of the mass accreting objects are older than 10 Myr. For each PMS star in Trumpler 14 we determine the mass accretion rate (Ṁacc) and discuss its dependence on mass and age. We finally combine the optical photometry with near-IR observations to build the spectral energy distribution (SED) for each PMS star in Tr 14. The analysis of the SEDs suggests the presence of transitional discs in which a large amount of gas is still present and sustains accretion onto the PMS object at ages older than 10 Myr. Our results, discussed in light of recent recent discoveries with Herschel of transitional discs containing a massive gas component around the relatively old PMS stars TW Hydrae, 49 Ceti, and HD 95086, support a new scenario n which old and evolved debris discs still host a significant amount of gas. Aims: Methods: Results:

  9. Stationary axisymmetric configuration of the resistive thick accretion tori around a Schwarzschild black hole

    NASA Astrophysics Data System (ADS)

    Shaghaghian, M.

    2016-02-01

    We examine a thick accretion disc in the presence of external gravity and intrinsic dipolar magnetic field due to a non-rotating central object. In this paper, we generalize the Newtonian theory of stationary axisymmetric resistive tori of Tripathy, Prasanna & Das by including the fully general relativistic features. If we are to obtain the steady state configuration, we have to take into account the finite resistivity for the magnetofluid in order to avoid the piling up of the field lines anywhere in the accretion discs. The efficient value of conductivity must be much smaller than the classical conductivity to be astrophysically interesting. The accreting plasma in the presence of an external dipole magnetic field gives rise to a current in the azimuthal direction. The azimuthal current produced due to the motion of the magnetofluid modifies the magnetic field structure inside the disc and generates a poloidal magnetic field for the disc. The solutions we have found show that the radial inflow, pressure and density distributions are strongly modified by the electrical conductivity both in relativistic and Newtonian regimes. However, the range of conductivity coefficient is different for both regimes, as well as that of the angular momentum parameter and the radius of the innermost stable circular orbit. Furthermore, it is shown that the azimuthal velocity of the disc which is not dependent on conductivity is sub-Keplerian in all radial distances for both regimes. Owing to the presence of pressure gradient and magnetic forces. This work may also be important for the general relativistic computational magnetohydrodynamics that suffers from the lack of exact analytic solutions that are needed to test computer codes.

  10. Thin-disc theory with a non-zero-torque boundary condition and comparisons with simulations

    NASA Astrophysics Data System (ADS)

    Penna, Robert F.; Sąowski, Aleksander; McKinney, Jonathan C.

    2012-02-01

    We present an analytical solution for thin-disc accretion on to a Kerr black hole that extends the standard Novikov-Thorne α-disc in three ways: (i) it incorporates non-zero stresses at the inner edge of the disc; (ii) it extends into the plunging region; and (iii) it uses a corrected vertical gravity formula. The free parameters of the model are unchanged. Non-zero boundary stresses are included by replacing the Novikov-Thorne no-torque boundary condition with the less strict requirement that the fluid velocity at the innermost stable circular orbit is the sound speed, which numerical models show to be the correct behaviour for luminosities below ˜30 per cent Eddington. We assume the disc is thin so we can ignore advection. Boundary stresses scale as αh and advection terms scale as h2 [where h is the disc opening angle (h=H/r)], so the model is self-consistent when h < α. We compare our solution with slim-disc models and general relativistic magnetohydrodynamic disc simulations. The model may improve the accuracy of black hole spin measurements.

  11. Three-dimensional, global, radiative GRMHD simulations of a thermally unstable disc

    NASA Astrophysics Data System (ADS)

    Mishra, B.; Fragile, P. C.; Johnson, C. L.; Kluźniak, W.

    2016-09-01

    We present results of a set of three-dimensional, general relativistic radiation magnetohydrodynamics simulations of thin accretion discs around a non-rotating black hole to test their thermal stability. We consider two cases, one that is initially radiation-pressure dominated and expected to be thermally unstable and another that is initially gas-pressure dominated and expected to remain stable. Indeed, we find that cooling dominates over heating in the radiation-pressure-dominated model, causing the disc to collapse vertically on roughly the local cooling timescale. We also find that heating and cooling within the disc have a different dependence on the mid-plane pressure-a prerequisite of thermal instability. Comparison of our data with the relevant thin-disc thermal equilibrium curve suggests that our disc may be headed for the thermally stable, gas-pressure-dominated branch. However, because the disc collapses to the point that we are no longer able to resolve it, we had to terminate the simulation. On the other hand, the gas-pressure-dominated model, which was run for twice as long as the radiation-pressure-dominated one, remains stable, with heating and cooling roughly in balance. Finally, the radiation pressure dominated simulation shows some evidence of viscous instability. The strongest evidence is in plots of surface density, which show the disc breaking up into rings.

  12. 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.

  13. 26 CFR 1.6011-2 - Returns, etc., of DISC's and former DISC's.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 26 Internal Revenue 13 2012-04-01 2012-04-01 false Returns, etc., of DISC's and former DISC's. 1.6011-2 Section 1.6011-2 Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY...., of DISC's and former DISC's. (a) Records and information. Every DISC and former DISC (as defined...

  14. 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. PMID:26601307

  15. Swings between rotation and accretion power in a binary millisecond pulsar.

    PubMed

    Papitto, A; Ferrigno, C; Bozzo, E; Rea, N; Pavan, L; Burderi, L; Burgay, M; Campana, S; Di Salvo, T; Falanga, M; Filipović, M D; Freire, P C C; Hessels, J W T; Possenti, A; Ransom, S M; Riggio, A; Romano, P; Sarkissian, J M; Stairs, I H; Stella, L; Torres, D F; Wieringa, M H; Wong, G F

    2013-09-26

    It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron star's rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales.

  16. Swings between rotation and accretion power in a binary millisecond pulsar.

    PubMed

    Papitto, A; Ferrigno, C; Bozzo, E; Rea, N; Pavan, L; Burderi, L; Burgay, M; Campana, S; Di Salvo, T; Falanga, M; Filipović, M D; Freire, P C C; Hessels, J W T; Possenti, A; Ransom, S M; Riggio, A; Romano, P; Sarkissian, J M; Stairs, I H; Stella, L; Torres, D F; Wieringa, M H; Wong, G F

    2013-09-26

    It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron star's rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales. PMID:24067710

  17. 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.

  18. 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

  19. Hot accretion flow with radiative cooling: state transitions in black hole X-ray binaries

    NASA Astrophysics Data System (ADS)

    Wu, Mao-Chun; Xie, Fu-Guo; Yuan, Ye-Fei; Gan, Zhaoming

    2016-06-01

    We investigate state transitions in black hole X-ray binaries through different parameters by using two-dimensional axisymmetric hydrodynamical simulation method. For radiative cooling in hot accretion flow, we take into account the bremsstrahlung, synchrotron and synchrotron self-Comptonization self-consistently in the dynamics. Our main result is that the state transitions occur when the accretion rate reaches a critical value dot{M} ˜ 3α dot{M}_Edd, above which cold and dense clumpy/filamentary structures are formed, embedded within the hot gas. We argued this mode likely corresponds to the proposed two-phase accretion model, which may be responsible for the intermediate state of black hole X-ray binaries. When the accretion rate becomes sufficiently high, the clumpy/filamentary structures gradually merge and settle down on to the mid-plane. Eventually the accretion geometry transforms to a disc-corona configuration. In summary, our results are consistent with the truncated accretion scenario for the state transition.

  20. 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.

  1. 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.

  2. Self consistent modeling of accretion columns in accretion powered pulsars

    NASA Astrophysics Data System (ADS)

    Falkner, Sebastian; Schwarm, Fritz-Walter; Wolff, Michael Thomas; Becker, Peter A.; Wilms, Joern

    2016-04-01

    We combine three physical models to self-consistently derive the observed flux and pulse profiles of neutron stars' accretion columns. From the thermal and bulk Comptonization model by Becker & Wolff (2006) we obtain seed photon continua produced in the dense inner regions of the accretion column. In a thin outer layer these seed continua are imprinted with cyclotron resonant scattering features calculated using Monte Carlo simulations. The observed phase and energy dependent flux corresponding to these emission profiles is then calculated, taking relativistic light bending into account. We present simulated pulse profiles and the predicted dependency of the observable X-ray spectrum as a function of pulse phase.

  3. On the dynamics of planetesimals embedded in turbulent protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Nelson, Richard P.; Gressel, Oliver

    2010-12-01

    Angular momentum transport and accretion in protoplanetary discs are generally believed to be driven by magnetohydrodynamics (MHD) turbulence via the magnetorotational instability (MRI). The dynamics of solid bodies embedded in such discs (dust grains, boulders, planetesimals and planets) may be strongly affected by the turbulence, such that the formation pathways for planetary systems are determined in part by the strength and spatial distribution of the turbulent flow. We examine the dynamics of planetesimals, with radii between 1m and 10km, embedded in turbulent protoplanetary discs, using 3D MHD simulations. The planetesimals experience gas drag and stochastic gravitational forces due to the turbulent disc. We use, and compare the results from, local shearing box simulations and global models in this study. The main aims of this work are to examine: the growth, and possible saturation, of the velocity dispersion of embedded planetesimals as a function of their size and disc parameters; the rate of radial migration and diffusion of planetesimals; the conditions under which the results from shearing box and global simulations agree. We find good agreement between local and global simulations when shearing boxes of dimension 4H × 16H × 2H are used (H being the local scaleheight). The magnitude of the density fluctuations obtained is sensitive to the box size, due to the excitation and propagation of spiral density waves. This affects the stochastic forcing experienced by planetesimals. The correlation time associated with the stochastic forcing is also found to be a function of the box size and aspect ratio. The equilibrium radial velocity dispersion, σ(vr), obtained depends on the radii, Rp, of the planetesimals. Bodies with Rp = 50m achieve the smallest value with σ(vr) ~= 20ms-1. Smaller bodies are tightly coupled to the gas, and boulders with Rp = 1m attain a value of σ(vr) similar to the turbulent velocity of the gas (~100ms-1). Equilibrium values of

  4. Sad or Fearful? The Influence of Body Posture on Adults' and Children's Perception of Facial Displays of Emotion

    ERIC Educational Resources Information Center

    Mondloch, Catherine J.

    2012-01-01

    The current research investigated the influence of body posture on adults' and children's perception of facial displays of emotion. In each of two experiments, participants categorized facial expressions that were presented on a body posture that was congruent (e.g., a sad face on a body posing sadness) or incongruent (e.g., a sad face on a body…

  5. Respiratory sinus arrhythmia reactivity to a sad film predicts depression symptom improvement and symptomatic trajectory.

    PubMed

    Panaite, Vanessa; Hindash, Alexandra Cowden; Bylsma, Lauren M; Small, Brent J; Salomon, Kristen; Rottenberg, Jonathan

    2016-01-01

    Respiratory sinus arrhythmia (RSA) reactivity, an index of cardiac vagal tone, has been linked to self-regulation and the severity and course of depression (Rottenberg, 2007). Although initial data supports the proposition that RSA withdrawal during a sad film is a specific predictor of depression course (Fraguas, 2007; Rottenberg, 2005), the robustness and specificity of this finding are unclear. To provide a stronger test, RSA reactivity to three emotion films (happy, sad, fear) and to a more robust stressor, a speech task, were examined in currently depressed individuals (n=37), who were assessed for their degree of symptomatic improvement over 30weeks. Robust RSA reactivity to the sad film uniquely predicted overall symptom improvement over 30weeks. RSA reactivity to both sad and stressful stimuli predicted the speed and maintenance of symptomatic improvement. The current analyses provide the most robust support to date that RSA withdrawal to sad stimuli (but not stressful) has specificity in predicting the overall symptomatic improvement. In contrast, RSA reactivity to negative stimuli (both sad and stressful) predicted the trajectory of depression course. Patients' engagement with sad stimuli may be an important sign to attend to in therapeutic settings. PMID:26681648

  6. Radicular interdural lumbar disc herniation.

    PubMed

    Akhaddar, Ali; Boulahroud, Omar; Elasri, Abad; Elmostarchid, Brahim; Boucetta, Mohammed

    2010-07-01

    Intraradicular lumbar disc herniation is a rare complication of disc disease that is generally diagnosed only during surgery. The mechanism for herniated disc penetration into the intradural space is not known with certainty, but adhesion between the radicular dura and the posterior longitudinal ligament was suggested as the most important condition. The authors report the first case of an intraradicular lumbar disc herniation without subdural penetration; the disc hernia was lodged between the two radicular dura layers. The patient, a 34-year-old soldier, was admitted with a 12-month history of low back pain and episodic left sciatica. Neurologic examination showed a positive straight leg raising test on the left side without sensory, motor or sphincter disturbances. Spinal CT scan and MRI exploration revealed a left posterolateral osteophyte formation at the L5-S1 level with an irregular large disc herniation, which migrated superiorly. An intradural extension was suspected. A left L5 hemilaminectomy and S1 foraminotomy were performed. The exploration revealed a large fragment of disc material located between the inner and outer layers of the left S1 radicular dura. The mass was extirpated without cerebrospinal fluid outflow. The postoperative course was uneventful. Radicular interdural lumbar disc herniation should be suspected when a swollen, hard and immobile nerve root is present intraoperatively.

  7. The origin of UV-optical variability in AGN and test of disc models: XMM-Newton and ground-based observations of NGC 4395

    NASA Astrophysics Data System (ADS)

    McHardy, I. M.; Connolly, S. D.; Peterson, B. M.; Bieryla, A.; Chand, H.; Elvis, M. S.; Emmanoulopoulos, D.; Falco, E.; Gandhi, P.; Kaspi, S.; Latham, D.; Lira, P.; McCully, C.; Netzer, H.; Uemura, M.

    2016-05-01

    The origin of short timescale (weeks/months) variability of AGN, whether due to intrinsic disc variations or reprocessing of X-ray emission by a surrounding accretion disc, has been a puzzle for many years. However recently a number of observational programmes, particularly of NGC 5548 with Swift, have shown that the UV/optical variations lag behind the X-ray variations in a manner strongly supportive of X-ray reprocessing. Somewhat surprisingly, the implied size of the accretion disc is ∼3 times greater than expected from a standard, smooth, Shakura-Sunyaev thin disc model. Although the difference may be explained by a clumpy accretion disc, it is not clear whether the difference will occur in all AGN or whether it may change as, eg, a function of black hole mass, accretion rate, or disc temperature. Measurements of interband lags for most AGN require long timescale monitoring, which is hard to arrange. However for low mass (< 106 M⊙) AGN, the combination of XMM-Newton EPIC (X-rays) with the optical monitor in fast readout mode allows an X-ray/UV-optical lag to be measured within a single long observation. Here we summarise previous related observations and report on XMM-Newton observations of NGC 4395 (mass 100 times lower, accretion rate ∼20 times lower than for NGC 5548). We find that the UVW1 lags the X-rays by ∼ 470 s. Simultaneous observations at 6 different ground based observatories also allowed the g-band lag (∼ 800s) to be measured. These observations are in agreement with X-ray reprocessing but initial analysis suggests that, for NGC 4395, they do not differ markedly from the predictions of the standard thin disc model.

  8. Hydrodynamic outcomes of planet scattering in transitional discs

    NASA Astrophysics Data System (ADS)

    Moeckel, Nickolas; Armitage, Philip J.

    2012-01-01

    A significant fraction of unstable multiple planet systems are likely to scatter during the transitional disc phase as gas damping becomes ineffectual. Using a large ensemble of FARGO hydrodynamic simulations and MERCURY N-body integrations, we directly follow the dynamics of planet-disc and planet-planet interactions through the clearing phase and through 50 Myr of planetary system evolution. Disc clearing is assumed to occur as a result of X-ray-driven photoevaporation. We find that the hydrodynamic evolution of individual scattering systems is complex, and can involve phases in which massive planets orbit within eccentric gaps, or accrete directly from the disc without a gap. Comparing the results to a reference gas-free model, we find that the N-body dynamics and hydrodynamics of scattering into one- and two-planet final states are almost identical. The eccentricity distributions in these channels are almost unaltered by the presence of gas. The hydrodynamic simulations, however, also form a population of low-eccentricity three-planet systems in long-term stable configurations, which are not found in N-body runs. The admixture of these systems results in modestly lower eccentricities in hydrodynamic as opposed to gas-free simulations. The precise incidence of these three-planet systems is likely a function of the initial conditions; different planet set-ups (number or spacing) may change the quantitative character of this result. We analyse the properties of surviving multiple planet systems, and show that only a small fraction (a few per cent) enter mean motion resonances after scattering, while a larger fraction form stable resonant chains and avoid scattering entirely. Our results remain consistent with the hypothesis that exoplanet eccentricity results from scattering, though the detailed agreement between observations and gas-free simulation results is likely coincidental. We discuss the prospects for further tests of scattering models by observing planets

  9. Simulations of magnetic fields in isolated disc galaxies

    NASA Astrophysics Data System (ADS)

    Pakmor, Rüdiger; Springel, Volker

    2013-06-01

    Magnetic fields are known to be dynamically important in the interstellar medium of our own Galaxy, and they are ubiquitously observed in diffuse gas in the haloes of galaxies and galaxy clusters. Yet, magnetic fields have typically been neglected in studies of the formation of galaxies, leaving their global influence on galaxy formation largely unclear. Here we extend our magnetohydrodynamics (MHD) implementation in the moving-mesh code AREPO to cosmological problems which include radiative cooling and the formation of stars. In particular, we replace our previously employed divergence cleaning approach with a Powell eight-wave scheme, which turns out to be significantly more stable, even in very dynamic environments. We verify the improved accuracy through simulations of the magneto-rotational instability in accretion discs, which reproduce the correct linear growth rate of the instability. Using this new MHD code, we simulate the formation of isolated disc galaxies similar to the Milky Way using idealized initial conditions with and without magnetic fields. We find that the magnetic field strength is quickly amplified in the initial central starburst and the differential rotation of the forming disc, eventually reaching a saturation value. At this point, the magnetic field pressure in the interstellar medium becomes comparable to the thermal pressure, and a further efficient growth of the magnetic field strength is prevented. The additional pressure component leads to a lower star formation rate at late times compared to simulations without magnetic fields, and induces changes in the spiral arm structures of the gas disc. In addition, we observe highly magnetized fountain-like outflows from the disc. These results are robust with numerical resolution and are largely independent of the initial magnetic seed field strength assumed in the initial conditions, as the amplification process is rapid and self-regulated. Our findings suggest an important influence of

  10. The origins of active galactic nuclei obscuration: the 'torus' as a dynamical, unstable driver of accretion

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.; Hayward, Christopher C.; Narayanan, Desika; Hernquist, Lars

    2012-02-01

    Recent multiscale simulations have made it possible to follow gas inflows responsible for high-Eddington ratio accretion on to massive black holes (BHs) from galactic scales to the BH accretion disc. When sufficient gas is driven towards a BH, gravitational instabilities generically form lopsided, eccentric discs that propagate inwards from larger radii. The lopsided stellar disc exerts a strong torque on the gas, driving inflows that fuel the growth of the BH. Here, we investigate the possibility that the same disc, in its gas-rich phase, is the putative 'torus' invoked to explain obscured active galactic nuclei (AGN) and the cosmic X-ray background. The disc is generically thick and has characteristic ˜1-10 pc sizes and masses resembling those required of the torus. Interestingly, the scale heights and obscured fractions of the predicted torii are substantial even in the absence of strong stellar feedback providing the vertical support. Rather, they can be maintained by strong bending modes and warps/twists excited by the inflow-generating instabilities. A number of other observed properties commonly attributed to 'feedback' processes may in fact be explained entirely by dynamical, gravitational effects: the lack of alignment between torus and host galaxy, correlations between local star formation rate (SFR) and turbulent gas velocities and the dependence of obscured fractions on AGN luminosity or SFR. We compare the predicted torus properties with observations of gas surface density profiles, kinematics, scale heights and SFR densities in AGN, and find that they are consistent in all cases. We argue that it is not possible to reproduce these observations and the observed column density distribution without a clumpy gas distribution, but allowing for simple clumping on small scales the predicted column density distribution is in good agreement with observations from NH˜ 1020-1027 cm-2. We examine how the NH distribution scales with galaxy and AGN properties

  11. Hyper-Eddington mass accretion on to a black hole with super-Eddington luminosity

    NASA Astrophysics Data System (ADS)

    Sakurai, Yuya; Inayoshi, Kohei; Haiman, Zoltán

    2016-10-01

    We perform 1D radiation hydrodynamical simulations to solve accretion flows on to massive black holes (BHs) with a very high rate. Assuming that photon trapping limits the luminosity emerging from the central region to L ≲ LEdd, Inayoshi, Haiman & Ostriker (2016) have shown that an accretion flow settles to a `hyper-Eddington solution, with a steady and isothermal (T ≃ 8000 K) Bondi profile reaching ≳ 5000 times the Eddington accretion rate dot{M}_Eddequiv L_Edd/c^2. Here, we address the possibility that gas accreting with finite angular momentum forms a bright nuclear accretion disc, with a luminosity exceeding the Eddington limit (1 ≲ L/LEdd ≲ 100). Combining our simulations with an analytic model, we find that a transition to steady hyper-Eddington accretion still occurs, as long as the luminosity remains below L/LEdd ≲ 35 (MBH/104 M⊙)3/2(n∞/105 cm-3)(T∞/104 K)-3/2(r⋆/1014 cm)-1/2, where n∞ and T∞ are the density and temperature of the ambient gas, and r⋆ is the radius of the photosphere, at which radiation emerges. If the luminosity exceeds this value, accretion becomes episodic. Our results can be accurately recovered in a toy model of an optically thick spherical shell, driven by radiation force into a collapsing medium. When the central source is dimmer than the above critical value, the expansion of the shell is halted and reversed by ram pressure of the collapsing medium, and by shell's weight. Our results imply that rapid, unimpeded hyper-Eddington accretion is possible even if the luminosity of the central source far exceeds the Eddington limit, and can be either steady or strongly episodic.

  12. The Causal Connection Between Disc and Power-Law Variability in Hard State Black Hole X-Ray Binaries

    NASA Technical Reports Server (NTRS)

    Uttley, P.; Wilkinson, T.; Cassatella, P.; Wilms, J.; Pottschimdt, K.; Hanke, M.; Boeck, M.

    2010-01-01

    We use the XMM-Newton EPIC-pn instrument in timing mode to extend spectral time-lag studies of hard state black hole X-ray binaries into the soft X-ray band. \\Ve show that variations of the disc blackbody emission substantially lead variations in the power-law emission, by tenths of a second on variability time-scales of seconds or longer. The large lags cannot be explained by Compton scattering but are consistent with time-delays due to viscous propagation of mass accretion fluctuations in the disc. However, on time-scales less than a second the disc lags the power-law variations by a few ms, consistent with the disc variations being dominated by X-ray heating by the power-law, with the short lag corresponding to the light-travel time between the power-law emitting region and the disc. Our results indicate that instabilities in the accretion disc are responsible for continuum variability on time-scales of seconds or longer and probably also on shorter time-scales.

  13. A disc inside the bipolar planetary nebula M2-9

    NASA Astrophysics Data System (ADS)

    Lykou, F.; Chesneau, O.; Zijlstra, A. A.; Castro-Carrizo, A.; Lagadec, E.; Balick, B.; Smith, N.

    2011-03-01

    Aims: Bipolarity in proto-planetary and planetary nebulae is associated with events occurring in or around their cores. Past infrared observations have revealed the presence of dusty structures around the cores, many in the form of discs. Characterising those dusty discs provides invaluable constraints on the physical processes that govern the final mass expulsion of intermediate mass stars. We focus this study on the famous M2-9 bipolar nebula, where the moving lighthouse beam pattern indicates the presence of a wide binary. The compact and dense dusty core in the centre of the nebula can be studied by means of optical interferometry. Methods: M2-9 was observed with VLTI/MIDI at 39-47 m baselines with the UT2-UT3 and UT3-UT4 baseline configurations. These observations are interpreted using a dust radiative transfer Monte Carlo code. Results: A disc-like structure is detected perpendicular to the lobes, and a good fit is found with a stratified disc model composed of amorphous silicates. The disc is compact, 25 × 35 mas at 8 μm and 37 × 46 mas at 13 μm. For the adopted distance of 1.2 kpc, the inner rim of the disc is ~15 AU. The mass represents a few percent of the mass found in the lobes. The compactness of the disc puts strong constraints on the binary content of the system, given an estimated orbital period 90-120 yr. We derive masses of the binary components between 0.6-1.0 M⊙ for a white dwarf and 0.6-1.4 M⊙ for an evolved star. We present different scenarios on the geometric structure of the disc accounting for the interactions of the binary system, which includes an accretion disc as well. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, ESO N: 079.D-146.

  14. Double-disc gate valve

    DOEpatents

    Wheatley, Seth J.

    1979-01-01

    This invention relates to an improvement in a conventional double-disc gate valve having a vertically movable gate assembly including a wedge, spreaders slidably engaged therewtih, a valve disc carried by the spreaders. When the gate assembly is lowered to a selected point in the valve casing, the valve discs are moved transversely outward to close inlet and outlet ports in the casing. The valve includes hold-down means for guiding the disc-and-spreader assemblies as they are moved transversely outward and inward. If such valves are operated at relatively high differential pressures, they sometimes jam during opening. Such jamming has been a problem for many years in gate valves used in gaseous diffusion plants for the separtion of uranium isotopes. The invention is based on the finding that the above-mentioned jamming results when the outlet disc tilts about its horizontal axis in a certain way during opening of the valve. In accordance with the invention, tilting of the outlet disc is maintained at a tolerable value by providing the disc with a rigid downwardly extending member and by providing the casing with a stop for limiting inward arcuate movement of the member to a preselected value during opening of the valve.

  15. Discs in misaligned binary systems

    NASA Astrophysics Data System (ADS)

    Rawiraswattana, Krisada; Hubber, David A.; Goodwin, Simon P.

    2016-08-01

    We perform SPH simulations to study precession and changes in alignment between the circumprimary disc and the binary orbit in misaligned binary systems. We find that the precession process can be described by the rigid-disc approximation, where the disc is considered as a rigid body interacting with the binary companion only gravitationally. Precession also causes change in alignment between the rotational axis of the disc and the spin axis of the primary star. This type of alignment is of great important for explaining the origin of spin-orbit misaligned planetary systems. However, we find that the rigid-disc approximation fails to describe changes in alignment between the disc and the binary orbit. This is because the alignment process is a consequence of interactions that involve the fluidity of the disc, such as the tidal interaction and the encounter interaction. Furthermore, simulation results show that there are not only alignment processes, which bring the components towards alignment, but also anti-alignment processes, which tend to misalign the components. The alignment process dominates in systems with misalignment angle near 90°, while the anti-alignment process dominates in systems with the misalignment angle near 0° or 180°. This means that highly misaligned systems will become more aligned but slightly misaligned systems will become more misaligned.

  16. HOYLE-LYTTLETON ACCRETION IN THREE DIMENSIONS

    SciTech Connect

    Blondin, John M.; Raymer, Eric

    2012-06-10

    We investigate the stability of gravitational accretion of an ideal gas onto a compact object moving through a uniform medium at Mach 3. Previous three-dimensional simulations have shown that such accretion is not stable, and that strong rotational 'disk-like' flows are generated and accreted on short timescales. We re-address this problem using overset spherical grids that provide a factor of seven improvement in spatial resolution over previous simulations. With our higher spatial resolution we found these three-dimensional accretion flows remained remarkably axisymmetric. We examined two cases of accretion with different sized accretors. The larger accretor produced very steady flow, with the mass accretion rate varying by less than 0.02% over 30 flow times. The smaller accretor exhibited an axisymmetric breathing mode that modulated the mass accretion rate by a constant 20%. Nonetheless, the flow remained highly axisymmetric with only negligible accretion of angular momentum in both cases.

  17. Minding one's emotions: mindfulness training alters the neural expression of sadness.

    PubMed

    Farb, Norman A S; Anderson, Adam K; Mayberg, Helen; Bean, Jim; McKeon, Deborah; Segal, Zindel V

    2010-02-01

    Recovery from emotional challenge and increased tolerance of negative affect are both hallmarks of mental health. Mindfulness training (MT) has been shown to facilitate these outcomes, yet little is known about its mechanisms of action. The present study employed functional MRI (fMRI) to compare neural reactivity to sadness provocation in participants completing 8 weeks of MT and waitlisted controls. Sadness resulted in widespread recruitment of regions associated with self-referential processes along the cortical midline. Despite equivalent self-reported sadness, MT participants demonstrated a distinct neural response, with greater right-lateralized recruitment, including visceral and somatosensory areas associated with body sensation. The greater somatic recruitment observed in the MT group during evoked sadness was associated with decreased depression scores. Restoring balance between affective and sensory neural networks-supporting conceptual and body based representations of emotion-could be one path through which mindfulness reduces vulnerability to dysphoric reactivity.

  18. 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.

  19. ['A sad and painful heart'--Andreas Vesalius as cardiologist].

    PubMed

    Haneveld, G T

    1993-01-01

    One needs courage to dissociate oneself from ideas maintained for ages and put forward by authorities. How laborious this process has been for Vesalius concerning the heart, is obvious when we compare the information of an eye-witness with both editions of the De Humani Corporis Fabrica (1543 and 1555). He must have come hesitantly to the conclusion that the views on the permeability of the septum cordis, as they were supported by Galen, Mondino and Johann Winther, a professor at Louvain, could not be defended. However, they had been essential in the considerations about the blood-flow. Although Vesalius demonstrated by vivisection-experiments that a relation exists between the pulse and the heart contractions, he was not an experimenting cardiophysiologist. In this respect, he stood far behind his contemporary Leonardo da Vinci, who made experiments on heart ntractions and the bloodstream along the heart valves. Vesalius was an anatomist! And a morphologist! But he was also a physician. In this respect, he also was interested in the pathological aspects of anatomy. So he recalled in, his last book, Anatomicarum Gabrielis Fallopii Observationum Examen (1564) some cardiologically interesting patients, a.o. the courtier van Immerseel, with a very unequal pulse and "a sad and painful heart" (tristi in corde, sensu doloreve), by whom a heart abnormality was found post mortem, that in modern terms we could call "an old heart infarction with thrombus formation." According to Schenk von Grafenberg, Vesalius was dreaming of a big book about anatomo-pathology, but alas, he never wrote it. Undoubtedly he would have trusted more his eyes and less Galen: "non solum ex Galenis testimonio, sed etiam oculis ipsis perspexeris". PMID:8209581

  20. ['A sad and painful heart'--Andreas Vesalius as cardiologist].

    PubMed

    Haneveld, G T

    1993-01-01

    One needs courage to dissociate oneself from ideas maintained for ages and put forward by authorities. How laborious this process has been for Vesalius concerning the heart, is obvious when we compare the information of an eye-witness with both editions of the De Humani Corporis Fabrica (1543 and 1555). He must have come hesitantly to the conclusion that the views on the permeability of the septum cordis, as they were supported by Galen, Mondino and Johann Winther, a professor at Louvain, could not be defended. However, they had been essential in the considerations about the blood-flow. Although Vesalius demonstrated by vivisection-experiments that a relation exists between the pulse and the heart contractions, he was not an experimenting cardiophysiologist. In this respect, he stood far behind his contemporary Leonardo da Vinci, who made experiments on heart ntractions and the bloodstream along the heart valves. Vesalius was an anatomist! And a morphologist! But he was also a physician. In this respect, he also was interested in the pathological aspects of anatomy. So he recalled in, his last book, Anatomicarum Gabrielis Fallopii Observationum Examen (1564) some cardiologically interesting patients, a.o. the courtier van Immerseel, with a very unequal pulse and "a sad and painful heart" (tristi in corde, sensu doloreve), by whom a heart abnormality was found post mortem, that in modern terms we could call "an old heart infarction with thrombus formation." According to Schenk von Grafenberg, Vesalius was dreaming of a big book about anatomo-pathology, but alas, he never wrote it. Undoubtedly he would have trusted more his eyes and less Galen: "non solum ex Galenis testimonio, sed etiam oculis ipsis perspexeris".

  1. Medical Information on Optical Disc*

    PubMed Central

    Schipma, Peter B.; Cichocki, Edward M.; Ziemer, Susan M.

    1987-01-01

    Optical discs may permit a revolutionary change in the distribution and use of medical information. A single compact disc, similar in size to that used for digital audio recording, can contain over 500 million characters of information that is accessible by a Personal Computer. These discs can be manufactured at a cost lower than that of print on paper, at reasonable volumes. Software can provide the health care professional with nearly instantaneous access to the information. Thus, for the first time, the opportunity exists to have large local medical information collections. This paper describes an application of this technology in the field of Oncology.

  2. The behavioural expression of empathy to others' pain versus others' sadness in young children.

    PubMed

    Bandstra, Nancy F; Chambers, Christine T; McGrath, Patrick J; Moore, Chris

    2011-05-01

    Little is known about how children develop or express their empathy for another individual's pain. The current study compared the behavioural expression of empathy for pain with that for emotion, specifically sadness, in children. One hundred twenty children (60 boys, 60 girls) between the ages of 18 and 36 months (M=26.44 months; SD=5.17) were assessed for their empathy-related behavioural responses to simulations of an adult's pain and sadness, each presented separately. Children were more likely to be distressed by, but also more likely to be prosocially responsive to, another's sadness. Conversely, children were more likely to actively play during another's pain. Despite these differences, principal component analyses conducted separately for pain and sadness revealed conceptual similarities across simulation type. Components labelled as Empathic Concern and Personal Distress emerged for both simulations. Hierarchical regression analyses examining the influence of developmental (ie, age, sex) and interindividual (ie, temperament, social-emotional development, language abilities) variables of interest in children's empathy-related responses were conducted for each pain and sadness component. Age differences emerged only for pain. There were no sex differences for either simulation. Temperament showed some predictive value in how children would respond to sadness. Social-emotional variables showed some predictive value in how children would respond to pain and sadness. Language showed very little predictive value. These findings highlight both conceptual similarities across, and important differences between, children's expressions of empathy for pain and for sadness. Pain appears to be more easily ignored and results in fewer prosocial responses in children.

  3. Magnetorotationally driven wind cycles in local disc models

    NASA Astrophysics Data System (ADS)

    Riols, A.; Ogilvie, G. I.; Latter, H.; Ross, J. P.

    2016-09-01

    Jets, from the protostellar to the AGN context, have been extensively studied but their connection to the turbulent dynamics of the underlying accretion disc is poorly understood. Following a similar approach to Lesur et al. (2013), we examine the role of the magnetorotational instability (MRI) in the production and acceleration of outflows from discs. Via a suite of one-dimensional shearing-box simulations of stratified discs we show that magneto-centrifugal winds exhibit cyclic activity with a period of 10 - 20 Ω-1, a few times the orbital period. The cycle seems to be more vigorous for strong vertical field; it is robust to the variation of relevant parameters and independent of numerical details. The convergence of these solutions (in particular the mass loss rate) with vertical box size is also studied. By considering a sequence of magnetohydrostatic equilibria and their stability, the periodic activity may be understood as the succession of the following phases: (a) a dominant MRI channel mode, (b) strong magnetic field generation, (c) consequent wind launching, and ultimately (d) vertical expulsion of the excess magnetic field by the expanding and accelerating gas associated with the wind. We discuss potential connections between this behaviour and observed time-variability in disk-jet systems.

  4. Compressive vs Solenoidal Turbulence and Violent Disc Instability

    NASA Astrophysics Data System (ADS)

    Mandelker, Nir; Dekel, Avishai; Inoue, Shigeki; Ceverino, Daniel; Primack, Joel

    2015-08-01

    High redshift star-forming galaxies (SFGs) exhibit star-formation rates (SFR) 20-100 times higher than local SFGs. This increased SFR is due to much higher gas fractions and surface densities prevalent in high redshift SFG. Such high gas fractions cause the disc to become violently unstable and undergo a phase of violent disc instability (VDI). During the VDI phase, there is rapid inflow of gas towards the galactic centre with inflow times comparable to the disc orbital time, which can lead to a compact "blue nugget". In addition, giant ~kpc scale star-forming clumps are formed, the most massive of which survive dtellar feedback and migrate towards the centre, where they coalesce in the growing bulge. While the existence of giant clumps is commonly associated with Toomre instability, high resolution cosmological simulations of galaxy formation show that active clump formation occurs even in regions where the Toomre Q parameter is well above the threshold for stability. The simulations suggest instead a non-linear instability, where frequent minor mergers and intense inflow by cold streams increase the compressive mode of turbulence relative to the solenoidal mode. We find this can induce clump formation even in regions that should be stable according to linear Toomre theory. Thus we show that mergers, smooth accretion from the cosmic web and VDI all go hand in hand in driving galaxy evolution at high redshift.

  5. The dynamics of inner dead-zone boundaries in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Latter, Henrik N.; Balbus, Steven

    2012-08-01

    In protoplanetary discs, the inner radial boundary between the MRI turbulent ('active') and MRI quiescent ('dead') zones plays an important role in models of the disc evolution and in some planet formation scenarios. In reality, this boundary is not well-defined: thermal heating from the star in a passive disc yields a transition radius close to the star (<0.1 au), whereas if the disc is already MRI active, it can self-consistently maintain the requisite temperatures out to a transition radius of roughly 1 au. Moreover, the interface may not be static; it may be highly fluctuating or else unstable. In this paper, we study a reduced model of the dynamics of the active/dead zone interface that mimics several important aspects of a real disc system. We find that MRI-transition fronts propagate inwards (a 'dead front' suppressing the MRI) if they are initially at the larger transition radius, or propagate outwards (an 'active front' igniting the MRI) if starting from the smaller transition radius. In both cases, the front stalls at a well-defined intermediate radius, where it remains in a quasi-static equilibrium. We propose that it is this new, intermediate stalling radius that functions as the true boundary between the active and dead zones in protoplanetary discs. These dynamics are likely implicated in observations of variable accretion, such as FU Ori outbursts, as well as in those planet formation theories that require the accumulation of solid material at the dead/active interface.

  6. Strong constraints on a super-Eddington accretion flow: XMM-Newton observations of an intermediate-mass black hole

    NASA Astrophysics Data System (ADS)

    Jin, Chichuan; Done, Chris; Ward, Martin

    2016-01-01

    RX J1140.1+0307 is a Narrow Line Seyfert 1 (NLS1) with one of the lowest black hole masses known in an AGN (M ≤ 106 M⊙). We show results from two new XMM-Newton observations, exhibiting soft 2-10 keV spectra, a strong excess at lower energies, and fast X-ray variability which is typical of this class of AGN. The soft excess can be equally well fit using either low-temperature Comptonization or highly smeared, ionized reflection models, but we additionally consider the fast X-ray variability to produce covariance, lag and coherence spectra to show that the low-temperature Comptonization model gives a better description of the break in variability properties between soft and hard X-rays. Both these models require an additional component at the softest energies, as expected from the accretion disc. However, standard disc models cannot connect this to the optical/UV emission from the outer disc unless the mass is underestimated by an order of magnitude. The variable optical and far UV emission instead suggests that L/LEdd ˜ 10 through the outer disc, in which case advection and/or wind losses are required to explain the observed broad-band spectral energy distribution. This implies that the accretion geometry close to the black hole is unlikely to be a flat disc as assumed in the recent X-ray reverberation mapping techniques.

  7. On Thermohaline Mixing in Accreting White Dwarfs

    NASA Astrophysics Data System (ADS)

    Koester, Detlev

    2015-06-01

    We discuss the recent claim that the thermohaline (“fingering”) instability is important in accreting white dwarfs, increasing the derived accretion fluxes potentially by orders of magnitude. We present an alternative view and conclude that at least in the steady state this is not the case and the current method of estimating accretion fluxes is correct.

  8. Disc Golf: Teaching a Lifetime Activity

    ERIC Educational Resources Information Center

    Eastham, Susan L.

    2015-01-01

    Disc golf is a lifetime activity that can be enjoyed by students of varying skill levels and abilities. Disc golf follows the principles of ball golf but is generally easier for students to play and enjoy success. The object of disc golf is similar to ball golf and involves throwing a disc from the teeing area to the target in as few throws as…

  9. Enlivening Physics, a Local Video Disc Project.

    ERIC Educational Resources Information Center

    McInerney, M.

    1989-01-01

    Describes how to make and use an inexpensive video disc of physics demonstrations. Discusses the background, production of the disc, subject of the disc including angular momentum, "monkey and the hunter" experiment, Doppler shift, pressure of a constant volume of gas thermometer, and wave effects, and using the disc in classroom. (YP)

  10. Disc pack cleaning table saves computer time

    NASA Technical Reports Server (NTRS)

    Guy, J. T., Sr.

    1970-01-01

    Disc pack holding table is support frame upon which computer disc pack is loaded and protective cover released. This combination permits manual off-line cleaning of disc pack storage units at any time without shutting down the computer, and eliminates on-line disc drive unit to hold pack during cleaning.

  11. Differences and similarities in postural alterations caused by sadness and depression.

    PubMed

    Rosario, Jose Luis; Bezerra Diógenes, Maria Suely; Mattei, Rita; Leite, José Roberto

    2014-10-01

    The present study investigated the existence of a relationship between depression and body posture in 40 women, aged between 20 and 30 years, who had normal body mass indices (or were underweight) and absence of neurological, psychiatric, or musculoskeletal disorders. The aim of the present study was to investigate the existence of a relationship between sadness, depression and the posture represented by the angle of Tales, head inclination, shoulder inclination, and forward head and shoulder protrusion. The degree of depression was rated on analogue scales representing current and usual depression and current and usual sadness and by the Beck Depression Inventory. The results indicated that a relationship exists between: Beck depression and the angle of Tales (p = 0.01), current depression and inclination of the head (p = 0.05) and inclination of the shoulders (p = 0.006), and usual depression and protrusion of the shoulder (p = 0.02). Inclination of the shoulders is associated with current sadness (p = 0.03; r = 0.443) and usual sadness (p = 0.04; r = 0.401). Usual sadness is also associated with protrusion of the shoulder (p = 0.05; r = 0.492). No associations were found with protrusion of the head and the emotional variables assessed. The conclusion was that depression and sadness might possibly change posture. Consequently, postural assessment and treatment may assist in diagnosing and treating depression. PMID:25440204

  12. The minor third communicates sadness in speech, mirroring its use in music.

    PubMed

    Curtis, Meagan E; Bharucha, Jamshed J

    2010-06-01

    There is a long history of attempts to explain why music is perceived as expressing emotion. The relationship between pitches serves as an important cue for conveying emotion in music. The musical interval referred to as the minor third is generally thought to convey sadness. We reveal that the minor third also occurs in the pitch contour of speech conveying sadness. Bisyllabic speech samples conveying four emotions were recorded by 9 actresses. Acoustic analyses revealed that the relationship between the 2 salient pitches of the sad speech samples tended to approximate a minor third. Participants rated the speech samples for perceived emotion, and the use of numerous acoustic parameters as cues for emotional identification was modeled using regression analysis. The minor third was the most reliable cue for identifying sadness. Additional participants rated musical intervals for emotion, and their ratings verified the historical association between the musical minor third and sadness. These findings support the theory that human vocal expressions and music share an acoustic code for communicating sadness.

  13. Regulation of sadness via acceptance or suppression in adult Attention Deficit Hyperactivity Disorder (ADHD).

    PubMed

    Matthies, Swantje; Philipsen, Alexandra; Lackner, Helmut Karl; Sadohara, Chiharu; Svaldi, Jennifer

    2014-12-15

    Emotion dysregulation is a recognized symptom of adult Attention Deficit Hyperactivity Disorder (ADHD). The aim of this study is to induce sadness in adults suffering from ADHD and to investigate the impact of emotion regulation strategies on sadness intensity, and psychophysiological measures. Thirty-six adults diagnosed with ADHD were randomly assigned to either expressive suppression (SUPP) or acceptance (ACC) of emotion. Sadness was induced using a film clip. Participants estimated the intensity of sadness and the perception of being overwhelmed with emotion before (T1), immediately after (T2) and 2 min after the film (T3). Physiological measures were obtained. Sadness induction was effective in both conditions. The perception of being overwhelmed with emotion increased between T1 and T2 in both conditions, but persisted until T3 only in the expressive suppression condition whereas a decrease was observed in the acceptance condition. In ADHD expressive suppression of sadness seems to be associated to a prolonged recovery from the perception of being overwhelmed with emotion. Emotion-regulation via acceptance in contrast appears to allow faster recovery from the perception of being overwhelmed with emotion. To our knowledge, this is the first study to identify suppression as a critical mediator between an induced emotion and delayed recovery from emotional reactions in adult ADHD.

  14. A sad mood increases attention to unhealthy food images in women with food addiction.

    PubMed

    Frayn, Mallory; Sears, Christopher R; von Ranson, Kristin M

    2016-05-01

    Food addiction and emotional eating both influence eating and weight, but little is known of how negative mood affects the attentional processes that may contribute to food addiction. The purpose of this study was to compare attention to food images in adult women (N = 66) with versus without food addiction, before and after a sad mood induction (MI). Participants' eye fixations were tracked and recorded throughout 8-s presentations of displays with healthy food, unhealthy food, and non-food images. Food addiction was self-reported using the Yale Food Addiction Scale. The sad MI involved watching an 8-min video about a young child who passed away from cancer. It was predicted that: (1) participants in the food addiction group would attend to unhealthy food significantly more than participants in the control group, and (2) participants in the food addiction group would increase their attention to unhealthy food images following the sad MI, due to increased emotional reactivity and poorer emotional regulation. As predicted, the sad MI had a different effect for those with versus without food addiction: for participants with food addiction, attention to unhealthy images increased following the sad MI and attention to healthy images decreased, whereas for participants without food addiction the sad MI did not alter attention to food. These findings contribute to researchers' understanding of the cognitive factors underlying food addiction. PMID:26873452

  15. Reduced heat pain thresholds after sad-mood induction are associated with changes in thalamic activity.

    PubMed

    Wagner, Gerd; Koschke, Mandy; Leuf, Tanja; Schlösser, Ralf; Bär, Karl-Jürgen

    2009-03-01

    Negative affective states influence pain processing in healthy subjects in terms of augmented pain experience. Furthermore, our previous studies revealed that patients with major depressive disorder showed increased heat pain thresholds on the skin. Potential neurofunctional correlates of this finding were located within the fronto-thalamic network. The aim of the present study was to investigate the neurofunctional underpinnings of the influence of sad mood upon heat pain processing in healthy subjects. For this purpose, we used a combination of the Velten Mood Induction procedure and a piece of music to induce sad affect. Initially we assessed heat pain threshold after successful induction of sad mood outside the MR scanner in Experiment 1. We found a highly significant reduction in heat pain threshold on the left hand and a trend for the right. In Experiment 2, we applied thermal pain stimuli on the left hand (37, 42, and 45 degrees C) in an MRI scanner. Subjects were scanned twice, one group before and after sad-mood induction and another group before and after neutral-mood induction, respectively. Our main finding was a significant group x mood-induction interaction bilaterally in the ventrolateral nucleus of the thalamus indicating a BOLD signal increase after sad-mood induction and a BOLD signal decrease in the control group. We present evidence that induced sad affect leads to reduced heat pain thresholds in healthy subjects. This is probably due to altered lateral thalamic activity, which is potentially associated with changed attentional processes.

  16. Decellularized allogeneic intervertebral disc: natural biomaterials for regenerating disc degeneration

    PubMed Central

    Hu, Zhijun; Chen, Kai; Shan, Zhi; Chen, Shuai; Wang, Jiying; Mo, Jian; Ma, Jianjun; Xu, Wenbing; Qin, An; Fan, Shunwu

    2016-01-01

    Intervertebral disc degeneration is associated with back pain and disc herniation. This study established a modified protocol for intervertebral disc (IVD) decellularization and prepared its extracellular matrix (ECM). By culturing mesenchymal stem cells (MSCs)(3, 7, 14 and 21 days) and human degenerative IVD cells (7 days) in the ECM, implanting it subcutaneously in rabbit and injecting ECM microparticles into degenerative disc, the biological safety and efficacy of decellularized IVD was evaluated both in vitro and in vivo. Here, we demonstrated that cellular components can be removed completely after decellularization and maximally retain the structure and biomechanics of native IVD. We revealed that allogeneic ECM did not evoke any apparent inflammatory reaction in vivo and no cytotoxicity was found in vitro. Moreover, IVD ECM can induce differentiation of MSCs into IVD-like cells in vitro. Furthermore, allogeneic ECM microparticles are effective on the treatment of rabbit disc degeneration in vivo. In conclusion, our study developed an optimized method for IVD decellularization and we proved decellularized IVD is safe and effective for the treatment of degenerated disc diseases. PMID:26933821

  17. 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.

  18. Optical effects related to Keplerian discs orbiting Kehagias-Sfetsos naked singularities

    NASA Astrophysics Data System (ADS)

    Stuchlík, Zdeněk; Schee, Jan

    2014-10-01

    We demonstrate possible optical signatures of the Kehagias-Sfetsos (KS) naked singularity spacetimes representing a spherically symmetric vacuum solution of the modified Hořava gravity. In such spacetimes, accretion structures significantly different from those present in standard black hole spacetimes occur due to the ‘antigravity’ effect, which causes an internal static sphere surrounded by Keplerian discs. We focus our attention on the optical effects related to the Keplerian accretion discs, constructing the optical appearance of the Keplerian discs, the spectral continuum due to their thermal radiation, and the spectral profiled lines generated in the innermost parts of such discs. The KS naked singularity signature is strongly encoded in the characteristics of predicted optical effects, especially in cases where the spectral continuum and spectral lines are profiled by the strong gravity of the spacetimes due to the vanishing region of the angular velocity gradient influencing the effectiveness of the viscosity mechanism. We can conclude that optical signatures of KS naked singularities can be well distinguished from the signatures of standard black holes.

  19. Imaginal Disc Transplantation in Drosophila.

    PubMed

    Katsuyama, Tomonori; Paro, Renato

    2016-01-01

    Since Ephrussi and Beadle introduced imaginal disc transplantation to Drosophila research in 1936, the method played an important part towards a better understanding of disc patterning, tissue regeneration, and reprogramming phenomena like transdetermination. Despite increasing usage of high-throughput approaches towards solving biological problems this classical manual method is still in use for studying disc development in a semi-physiological context. Here we describe in detail a protocol and provide recommendations on the procedure in particular for analyzing the regenerative potential of imaginal disks. The steps consist of disc dissection and fragmentation, transplantation into the larval or adult abdomen, and the recovery of implants from the host abdomen. Additionally, we also describe how to make the special transplantation needle from a glass capillary. PMID:27659995

  20. Percutaneous diode laser disc nucleoplasty

    NASA Astrophysics Data System (ADS)

    Menchetti, P. P.; Longo, Leonardo

    2004-09-01

    The treatment of herniated disc disease (HNP) over the years involved different miniinvasive surgical options. The classical microsurgical approach has been substituted over the years both by endoscopic approach in which is possible to practice via endoscopy a laser thermo-discoplasty, both by percutaneous laser disc nucleoplasty. In the last ten years, the percutaneous laser disc nucleoplasty have been done worldwide in more than 40000 cases of HNP. Because water is the major component of the intervertebral disc, and in HNP pain is caused by the disc protrusion pressing against the nerve root, a 980 nm Diode laser introduced via a 22G needle under X-ray guidance and local anesthesia, vaporizes a small amount of nucleous polposus with a disc shrinkage and a relief of pressure on nerve root. Most patients get off the table pain free and are back to work in 5 to 7 days. Material and method: to date, 130 patients (155 cases) suffering for relevant symptoms therapy-resistant 6 months on average before consulting our department, have been treated. Eightyfour (72%) males and 46 (28%) females had a percutaneous laser disc nucleoplasty. The average age of patients operated was 48 years (22 - 69). The level of disc removal was L3/L4 in 12 cases, L4/L5 in 87 cases and L5/S1 in 56 cases. Two different levels were treated at the same time in 25 patients. Results: the success rate at a minimum follow-up of 6 months was 88% with a complication rate of 0.5%.

  1. The growth of discs and bulges during hierarchical galaxy formation - I. Fast evolution versus secular processes

    NASA Astrophysics Data System (ADS)

    Tonini, C.; Mutch, S. J.; Croton, D. J.; Wyithe, J. S. B.

    2016-07-01

    We present a theoretical model for the evolution of mass, angular momentum and size of galaxy discs and bulges, and we implement it into the semi-analytic galaxy formation code, Semi-Analytic Galaxy Evolution. The model follows both secular and violent evolutionary channels, including smooth accretion, disc instabilities, minor and major mergers. We find that the combination of our recipe with hierarchical clustering produces two distinct populations of bulges: merger-driven bulges, akin to classical bulges and ellipticals, and instability-driven bulges, akin to secular (or pseudo-)bulges. The model mostly reproduces the mass-size relation of gaseous and stellar discs, the evolution of the mass-size relation of ellipticals, the Faber-Jackson relation, and the magnitude-colour diagram of classical and secular bulges. The model predicts only a small overlap of merger-driven and instability-driven components in the same galaxy, and predicts different bulge types as a function of galaxy mass and disc fraction. Bulge type also affects the star formation rate and colour at a given luminosity. The model predicts a population of merger-driven red ellipticals that dominate both the low-mass and high-mass ends of the galaxy population, and span all dynamical ages; merger-driven bulges in disc galaxies are dynamically old and do not interfere with subsequent evolution of the star-forming component. Instability-driven bulges dominate the population at intermediate galaxy masses, especially thriving in massive discs. The model green valley is exclusively populated by instability-driven bulge hosts. Through the present implementation, the mass accretion history is perceivable in the galaxy structure, morphology and colours.

  2. Rossby wave instability and long-term evolution of dead zones in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Miranda, Ryan; Lai, Dong; Méheut, Héloïse

    2016-04-01

    The physical mechanism of angular momentum transport in poorly ionized regions of protoplanetary discs, the dead zones (DZs), is not understood. The presence of a DZ naturally leads to conditions susceptible to the Rossby wave instability (RWI), which produces vortices and spiral density waves that may revive the DZ and be responsible for observed large-scale disc structures. We present a series of two-dimensional hydrodynamic simulations to investigate the role of the RWI in DZs, including its impact on the long-term evolution of the disc and its morphology. The non-linear RWI can generate Reynolds stresses (effective α parameter) as large as 0.01-0.05 in the DZ, helping to sustain quasi-steady accretion throughout the disc. It also produces novel disc morphologies, including azimuthal asymmetries with m = 1, 2, and atypical vortex shapes. The angular momentum transport strength and morphology are most sensitive to two parameters: the radial extent of the DZ and the disc viscosity. The largest Reynolds stresses are produced when the radial extent of the DZ is less than its distance to the central star. Such narrow DZs lead to a single vortex or two coherent antipodal vortices in the quasi-steady state. The edges of wider DZs evolve separately, resulting in two independent vortices and reduced angular momentum transport efficiency. In either case, we find that, because of the Reynolds stresses generated by the non-linear RWI, gravitational instability is unlikely to play a role in angular momentum transport across the DZ, unless the accretion rate is sufficiently high.

  3. Disc piezoelectric ceramic transformers.

    PubMed

    Erhart, Jirií; Půlpán, Petr; Doleček, Roman; Psota, Pavel; Lédl, Vít

    2013-08-01

    In this contribution, we present our study on disc-shaped and homogeneously poled piezoelectric ceramic transformers working in planar-extensional vibration modes. Transformers are designed with electrodes divided into wedge, axisymmetrical ring-dot, moonie, smile, or yin-yang segments. Transformation ratio, efficiency, and input and output impedances were measured for low-power signals. Transformer efficiency and transformation ratio were measured as a function of frequency and impedance load in the secondary circuit. Optimum impedance for the maximum efficiency has been found. Maximum efficiency and no-load transformation ratio can reach almost 100% and 52 for the fundamental resonance of ring-dot transformers and 98% and 67 for the second resonance of 2-segment wedge transformers. Maximum efficiency was reached at optimum impedance, which is in the range from 500 Ω to 10 kΩ, depending on the electrode pattern and size. Fundamental vibration mode and its overtones were further studied using frequency-modulated digital holographic interferometry and by the finite element method. Complementary information has been obtained by the infrared camera visualization of surface temperature profiles at higher driving power. PMID:25004532

  4. Disc piezoelectric ceramic transformers.

    PubMed

    Erhart, Jirií; Půlpán, Petr; Doleček, Roman; Psota, Pavel; Lédl, Vít

    2013-08-01

    In this contribution, we present our study on disc-shaped and homogeneously poled piezoelectric ceramic transformers working in planar-extensional vibration modes. Transformers are designed with electrodes divided into wedge, axisymmetrical ring-dot, moonie, smile, or yin-yang segments. Transformation ratio, efficiency, and input and output impedances were measured for low-power signals. Transformer efficiency and transformation ratio were measured as a function of frequency and impedance load in the secondary circuit. Optimum impedance for the maximum efficiency has been found. Maximum efficiency and no-load transformation ratio can reach almost 100% and 52 for the fundamental resonance of ring-dot transformers and 98% and 67 for the second resonance of 2-segment wedge transformers. Maximum efficiency was reached at optimum impedance, which is in the range from 500 Ω to 10 kΩ, depending on the electrode pattern and size. Fundamental vibration mode and its overtones were further studied using frequency-modulated digital holographic interferometry and by the finite element method. Complementary information has been obtained by the infrared camera visualization of surface temperature profiles at higher driving power.

  5. Stellar and quasar feedback in concert: effects on AGN accretion, obscuration, and outflows

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.; Torrey, Paul; Faucher-Giguère, Claude-André; Quataert, Eliot; Murray, Norman

    2016-05-01

    We study the interaction of feedback from active galactic nuclei (AGN) and a multiphase interstellar medium (ISM), in simulations including explicit stellar feedback, multiphase cooling, accretion-disc winds, and Compton heating. We examine radii ˜0.1-100 pc around a black hole (BH), where the accretion rate on to the BH is determined and where AGN-powered winds and radiation couple to the ISM. We conclude: (1) the BH accretion rate is determined by exchange of angular momentum between gas and stars in gravitational instabilities. This produces accretion rates ˜0.03-1 M⊙ yr-1, sufficient to power luminous AGN. (2) The gas disc in the galactic nucleus undergoes an initial burst of star formation followed by several million years where stellar feedback suppresses the star formation rate (SFR). (3) AGN winds injected at small radii with momentum fluxes ˜LAGN/c couple efficiently to the ISM and have dramatic effects on ISM properties within ˜100 pc. AGN winds suppress the nuclear SFR by factors ˜10-30 and BH accretion rate by factors ˜3-30. They increase the outflow rate from the nucleus by factors ˜10, consistent with observational evidence for galaxy-scale AGN-driven outflows. (4) With AGN feedback, the predicted column density distribution to the BH is consistent with observations. Absent AGN feedback, the BH is isotropically obscured and there are not enough optically thin sightlines to explain type-I AGN. A `torus-like' geometry arises self-consistently as AGN feedback evacuates gas in polar regions.

  6. Cyclotron Resonance in Accreting Pulsars

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Dipankar

    2016-07-01

    Cyclotron Resonance Absorption/Scattering features provide direct measurement of magnetic field strength in the line forming region. This has enabled the estimation of magnetic field strengths of nearly two dozen neutron stars in accreting high mass binary systems. With improved spectroscopic sensitivity, new X-ray observatories such as NuSTAR, Astrosat and Hitomi are opening the doors to studying detailed features such as the line shape and phase dependence with high significance. Such studies will help understand the nature of matter accumulation in, and outflow from, the magnetically confined accretion column on the neutron star. This talk will describe the results of MHD simulations of the matter flow in such systems, the diagnostics of such flows using cyclotron lines, and comparison with recent observations from NuSTAR and Astrosat.

  7. 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.

  8. MRI Evaluation of Lumbar Disc Degenerative Disease

    PubMed Central

    Patel, Rupal; Mehta, Chetan; Patel, Narrotam

    2015-01-01

    Introduction: Lower back pain secondary to degenerative disc disease is a condition that affects young to middle-aged persons with peak incidence at approximately 40 y. MRI is the standard imaging modality for detecting disc pathology due to its advantage of lack of radiation, multiplanar imaging capability, excellent spinal soft-tissue contrast and precise localization of intervertebral discs changes. Aims and Objective: To evaluate the characterization, extent, and changes associated with the degenerative lumbar disc disease by Magnetic Resonance Imaging. Study Design: Cross-sectional and observational study. Materials and Methods: A total 109 patients of the lumbar disc degeneration with age group between 17 to 80 y were diagnosed & studied on 1.5 Tesla Magnetic Resonance Imaging machine. MRI findings like lumbar lordosis, Schmorl’s nodes, decreased disc height, disc annular tear, disc herniation, disc bulge, disc protrusion and disc extrusion were observed. Narrowing of the spinal canal, lateral recess and neural foramen with compression of nerve roots observed. Ligamentum flavum thickening and facetal arthropathy was observed. Result: Males were more commonly affected in Degenerative Spinal Disease & most of the patients show loss of lumbar lordosis. Decreased disc height was common at L5-S1 level. More than one disc involvement was seen per person. L4 – L5 disc was the most commonly involved. Annular disc tear, disc herniation, disc extrusion, narrowing of spinal canal, narrowing of lateral recess, compression of neural foramen, ligamentum flavum thickening and facetal arthropathy was common at the L4 –L5 disc level. Disc buldge was common at L3 – L4 & L4 – L5 disc level. Posterior osteophytes are common at L3 - L4 & L5 –S1 disc level. L1- L2 disc involvement and spondylolisthesis are less common. Conclusion: Lumbar disc degeneration is the most common cause of low back pain. Plain radiograph can be helpful in visualizing gross anatomic changes in

  9. Controlling the collimation and rotation of hydromagnetic disc winds

    NASA Astrophysics Data System (ADS)

    Pudritz, Ralph E.; Rogers, Conrad S.; Ouyed, Rachid

    2006-02-01

    We present a comprehensive set of axisymmetric, time-dependent simulations of jets from Keplerian discs whose mass loading as a function of disc radius is systematically changed. For a reasonable model for the density structure and injection speed of the underlying accretion disc, mass loading is determined by the radial structure of the magnetic field of the disc. We vary this structure by using four different magnetic field configurations, ranging from the Ouyed-Pudritz `potential' configuration, to the increasingly more steeply falling Blandford-Payne and Pelletier-Pudritz models, and ending with a quite steeply raked configuration that bears similarities to the Shu X-wind model. We find that the radial distribution of the mass load has a profound effect on the rotational profile of the underlying jet as well as the degree of collimation of its outflow velocity and magnetic field lines. These four models have systematic differences in the power-law rotation profiles of jet material far from the source: vφ(r)~ra ranging over -0.46 >=a>=-0.76. We show analytically and confirm by our simulations that the collimation of a jet depends on its radial current distribution, which in turn is prescribed by the mass load. Models with steeply descending mass loads have strong toroidal fields, and these collimate to cylinders (this includes the Ouyed-Pudritz and Blandford-Payne outflows). On the other hand, the more gradually descending mass load profiles (the PP92 and monopolar distributions) have weaker toroidal fields and these result in wide-angle outflows with parabolic collimation. We also present detailed structural information about jets such as their radial profiles of jet density, toroidal magnetic field and poloidal jet speed, as well as an analysis of the bulk energetics of our different simulations. Our results are in excellent agreement with the predictions of asymptotic collimation for axisymmetric, stationary jets.

  10. Spherical accretion and AGN feedback

    NASA Astrophysics Data System (ADS)

    Nulsen, Paul

    2014-06-01

    For a supermassive black hole accreting from a hot, quasi-spherical atmosphere, it is almost inevitable that the fluid approximation fails inside some point within the Bondi radius, but well outside the black hole event horizon. Within the region where the particle mean free paths exceed the radius, the flow must be modeled in terms of the Fokker-Planck equation. In the absence of magnetic fields, it is analogous to the "loss cone" problem for consumption of stars by a black hole. The accretion rate is suppressed well below the Bondi accretion rate and a significant power must be conveyed outward for the flow to proceed. This situation is complicated significantly by the presence of a magnetic field, but I will argue that the main outcomes are similar. I will also argue that the power emerging from such a flow, although generally far too little to suppress cooling on large scales, is an important ingredient of the AGN feedback cycle on scales comparable to the Bondi radius.

  11. 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.

  12. AGN fuelling: Bridging Large and Small Scales - Overlapping Inflows as Catalysts of Accretion

    NASA Astrophysics Data System (ADS)

    Manuel Carmona Loaiza, Juan Manuel

    2015-05-01

    One of the biggest challenges in understanding the fuelling of supermassive black holes in active galactic nuclei (AGN) is not on accounting for the source of fuel, as a galaxy can comfortably supply the required mass budget, but on its actual delivery. While a clear picture has been developed for the large scale (~ kpc) down to the intermediate one (~ 100 pc), and for the smallest scales (~ 0.1 pc) where an accretion disc likely forms, a bridge that has proven difficult to build is that between ~ 100 pc and ~ 0.1 pc. It is feared that gas at these scales might still retain enough angular momentum and settle into a larger scale disc with very low or no inflow to form or replenish the inner accretion disc (on ~ 0.01 pc scales). In this Thesis, I present numerical simulations in which a rotating gaseous shell flows towards a SMBH because of its lack of rotational support. As inflow proceeds, gas from the shell impacts an already present nuclear (~ 10pc) disc. The cancellation of angular momentum and redistribution of gas, due to the misalignment between the angular momentum of the shell and that of the disc, is studied in this scenario. The underlying hypothesis is that even if transport of angular momentum at these scales may be inefficient, the interaction of an inflow with a nuclear disc would still provide a mechanism to bring mass inwards because of the cancellation of angular momentum. I quantify the amount of gas such a cancellation would bring to the central parsec under different circumstances: Co- and counter-rotation between the disc and the shell and the presence or absence of an initial turbulent kick; I also discuss the impact of self gravity in our simulations. The scenario we study is highly idealized and designed to capture the specific outcomes produced by the mechanism proposed. I find that angular momentum cancellation and redistribution via hydrodynamical shocks leads to sub-pc inflows enhanced by more than 2-3 orders of magnitude. In all of our

  13. Gender differences in the impact of daily sadness on 24-h heart rate variability.

    PubMed

    Verkuil, Bart; Brosschot, Jos F; Marques, Andrea H; Kampschroer, Kevin; Sternberg, Esther M; Thayer, Julian F

    2015-12-01

    Reduced heart rate variability (HRV) is proposed to mediate the relation between depressive symptoms and cardiovascular health problems. Yet, several studies have found that in women depression is associated with higher HRV levels, whereas in men depression is associated with lower HRV levels. So far, these studies have only examined gender differences in HRV levels using a single assessment. This study aimed to test the interactive effects of gender and sadness on ambulatory-assessed HRV levels. A sample of 60 (41 women) employees participated in an ambulatory study. HRV levels (mean of successive differences; MSD) were continuously measured for 24 h. During the daytime, hourly assessments of sadness and other mood states were taken, while depressive symptoms were assessed with the Center for Epidemiologic Studies Depression scale (CES-D). Gender differences were observed when examining the impact of average daily sadness on MSD. In women, but not in men, the total amount of sadness experienced during the day was associated with higher circadian MSD levels. These findings suggest that researchers need to take gender differences into account when examining the relation between sadness, HRV, and cardiovascular problems. PMID:26338472

  14. Recalling happy memories in remitted depression: a neuroimaging investigation of the repair of sad mood.

    PubMed

    Foland-Ross, Lara C; Cooney, Rebecca E; Joormann, Jutta; Henry, Melissa L; Gotlib, Ian H

    2014-06-01

    Major depressive disorder (MDD) is a recurrent mood disorder. The high rate of recurrence of MDD suggests the presence of stable vulnerability factors that place individuals with a history of major depression at an increased risk for the onset of another episode. Previous research has linked the remitted state, and therefore increased vulnerability for depressive relapse, with difficulties in the use of pleasant autobiographical memories to repair sad mood. In the present study, we examined the neural correlates of these difficulties. Groups of 16 currently euthymic, remitted depressed individuals and 16 healthy (control) women underwent functional magnetic resonance imaging (fMRI) during sad mood induction and during recovery from a sad mood state through recall of mood-incongruent positive autobiographical memories. Sad mood was induced in participants by using film clips; participants then recalled positive autobiographical memories, a procedure previously shown to repair negative affect. During both the sad mood induction and automatic mood regulation, control participants exhibited activation in the left ventrolateral prefrontal cortex (vlPFC) and cuneus; in contrast, remitted participants exhibited a decrease in activation in these regions. Furthermore, exploratory analyses revealed that reduced activation levels during mood regulation predicted a worsening of depressive symptoms at a 20-month follow-up assessment. These findings highlight a dynamic role of the vlPFC and cuneus in the experience and modulation of emotional states and suggest that functional anomalies of these brain regions are associated with a history of, and vulnerability to, depression.

  15. Puerarin attenuates learning and memory impairments and inhibits oxidative stress in STZ-induced SAD mice.

    PubMed

    Zhao, Shan-shan; Yang, Wei-na; Jin, Hui; Ma, Kai-ge; Feng, Gai-feng

    2015-12-01

    Puerarin (PUE), an isoflavone purified from the root of Pueraria lobata (Chinese herb), has been reported to attenuate learning and memory impairments in the transgenic mouse model of Alzheimer's disease (AD). In the present study, we tested PUE in a sporadic AD (SAD) mouse model which was induced by the intracerebroventricular injection of streptozotocin (STZ). The mice were administrated PUE (25, 50, or 100mg/kg/d) for 28 days. Learning and memory abilities were assessed by the Morris water maze test. After behavioral test, the biochemical parameters of oxidative stress (glutathione peroxidase (GSH-Px), superoxide dismutases (SOD), and malondialdehyde (MDA)) were measured in the cerebral cortex and hippocampus. The SAD mice exhibited significantly decreased learning and memory ability, while PUE attenuated these impairments. The activities of GSH-Px and SOD were decreased while MDA was increased in the SAD animals. After PUE treatment, the activities of GSH-Px and SOD were elevated, and the level of MDA was decreased. The middle dose PUE was more effective than others. These results indicate that PUE attenuates learning and memory impairments and inhibits oxidative stress in STZ-induced SAD mice. PUE may be a promising therapeutic agent for SAD. PMID:26511841

  16. Puerarin attenuates learning and memory impairments and inhibits oxidative stress in STZ-induced SAD mice.

    PubMed

    Zhao, Shan-shan; Yang, Wei-na; Jin, Hui; Ma, Kai-ge; Feng, Gai-feng

    2015-12-01

    Puerarin (PUE), an isoflavone purified from the root of Pueraria lobata (Chinese herb), has been reported to attenuate learning and memory impairments in the transgenic mouse model of Alzheimer's disease (AD). In the present study, we tested PUE in a sporadic AD (SAD) mouse model which was induced by the intracerebroventricular injection of streptozotocin (STZ). The mice were administrated PUE (25, 50, or 100mg/kg/d) for 28 days. Learning and memory abilities were assessed by the Morris water maze test. After behavioral test, the biochemical parameters of oxidative stress (glutathione peroxidase (GSH-Px), superoxide dismutases (SOD), and malondialdehyde (MDA)) were measured in the cerebral cortex and hippocampus. The SAD mice exhibited significantly decreased learning and memory ability, while PUE attenuated these impairments. The activities of GSH-Px and SOD were decreased while MDA was increased in the SAD animals. After PUE treatment, the activities of GSH-Px and SOD were elevated, and the level of MDA was decreased. The middle dose PUE was more effective than others. These results indicate that PUE attenuates learning and memory impairments and inhibits oxidative stress in STZ-induced SAD mice. PUE may be a promising therapeutic agent for SAD.

  17. Prediction of Happy-Sad Mood from Daily Behaviors and Previous Sleep History

    PubMed Central

    Sano, Akane; Yu, Amy; McHill, Andrew W.; Phillips, Andrew J. K.; Taylor, Sara; Jaques, Natasha; Klerman, Elizabeth B.; Picard, Rosalind W.

    2016-01-01

    We collected and analyzed subjective and objective data using surveys and wearable sensors worn day and night from 68 participants, for 30 days each, to address questions related to the relationships among sleep duration, sleep irregularity, self-reported Happy-Sad mood and other factors in college students. We analyzed daily and monthly behavior and physiology and identified factors that affect mood, including how accurately sleep duration and sleep regularity for the past 1-5 days classified the participants into high/low mood using support vector machines. We found statistically significant associations among sad mood and poor health-related factors. Behavioral factors such as the percentage of neutral social interactions and the total academic activity hours showed the best performance in separating the Happy-Sad mood groups. Sleep regularity was a more important discriminator of mood than sleep duration for most participants, although both variables predicted happy/sad mood with from 70-82% accuracy. The number of nights giving the best prediction of happy/sad mood varied for different groups of individuals. PMID:26737854

  18. A self-consistent model for the evolution of the gas produced in the debris disc of β Pictoris

    NASA Astrophysics Data System (ADS)

    Kral, Q.; Wyatt, M.; Carswell, R. F.; Pringle, J. E.; Matrà, L.; Juhász, A.

    2016-09-01

    This paper presents a self-consistent model for the evolution of gas produced in the debris disc of β Pictoris. Our model proposes that atomic carbon and oxygen are created from the photodissociation of CO, which is itself released from volatile-rich bodies in the debris disc due to grain-grain collisions or photodesorption. While the CO lasts less than one orbit, the atomic gas evolves by viscous spreading resulting in an accretion disc inside the parent belt and a decretion disc outside. The temperature, ionization fraction and population levels of carbon and oxygen are followed with the photodissociation region model CLOUDY, which is coupled to a dynamical viscous α model. We present new gas observations of β Pic, of C I observed with Atacama Pathfinder EXperiment and O I observed with Herschel, and show that these along with published C II and CO observations can all be explained with this new model. Our model requires a viscosity α > 0.1, similar to that found in sufficiently ionized discs of other astronomical objects; we propose that the magnetorotational instability is at play in this highly ionized and dilute medium. This new model can be tested from its predictions for high-resolution ALMA observations of C I. We also constrain the water content of the planetesimals in β Pic. The scenario proposed here might be at play in all debris discs and this model could be used more generally on all discs with C, O or CO detections.

  19. The JCMT Gould Belt Survey: low-mass protoplanetary discs from a SCUBA-2 census of NGC 1333

    NASA Astrophysics Data System (ADS)

    Dodds, P.; Greaves, J. S.; Scholz, A.; Hatchell, J.; Holland, W. S.; JCMT Gould Belt Survey Team

    2015-02-01

    NGC 1333 is a 1-2 Myr old cluster of stars in the Perseus molecular cloud. We used 850 μm data from the Gould Belt Survey with SCUBA-2 on the James Clerk Maxwell Telescope to measure or place limits on disc masses for 82 Class II sources in this cluster. Eight disc candidates were detected; one is estimated to have mass of about 9 MJup in dust plus gas, while the others host only 2-4 MJup of circumstellar material. None of these discs exceeds the threshold for the `minimum mass solar nebula' (MMSN). This reinforces previous claims that only a small fraction of Class II sources at an age of 1-2 Myr have discs exceeding the MMSN threshold and thus can form a planetary system like our own. However, other regions with similarly low fractions of MMSN discs (IC 348, UpSco, σ Ori) are thought to be older than NGC 1333. Compared with coeval regions, the exceptionally low fraction of massive discs in NGC 1333 cannot easily be explained by the effects of UV radiation or stellar encounters. Our results indicate that additional environmental factors significantly affect disc evolution and the outcome of planet formation by core accretion.

  20. Gravitoturbulence in magnetized protostellar discs

    NASA Astrophysics Data System (ADS)

    Riols, A.; Latter, H.

    2016-08-01

    Gravitational instability (GI) features in several aspects of protostellar disc evolution, most notably in angular momentum transport, fragmentation, and the outbursts exemplified by FU Ori and EX Lupi systems. The outer regions of protostellar discs may also be coupled to magnetic fields, which could then modify the development of GI. To understand the basic elements of their interaction, we perform local 2D ideal and resistive magnetohydrodynamics simulations with an imposed toroidal field. In the regime of moderate plasma beta, we find that the system supports a hot gravitoturbulent state, characterized by considerable magnetic energy and stress and a surprisingly large Toomre parameter Q ≳ 10. This result has potential implications for disc structure, vertical thickness, ionization, etc. Our simulations also reveal the existence of long-lived and dense `magnetic islands' or plasmoids. Lastly, we find that the presence of a magnetic field has little impact on the fragmentation criterion of the disc. Though our focus is on protostellar discs, some of our results may be relevant for the outer radii of AGN.

  1. Formation of massive stars by growing accretion

    NASA Astrophysics Data System (ADS)

    Maeder, Andre

    There are at present three scenarios for the formation of massive star. 1) The classical scenario of constant mass pre-Main Sequence (MS) evolution on the Kelvin-Helmholtz timescale. 2) The coalescence scenario, with merging of intermediate mass protostars. 3) The accretion scenario. The various arguments for and against these scenarios are briefly reviewed. We examine the pre-MS evolution of accreting stars for constant accretion rates and for accretion rates which are growing with the stellar masses. The location of the birthlines in the HRD and the lifetimes support accretion rates growing fastly with the stellar masses. Remarkably the dependence found is similar to that of the mass outflows from UC HII regions observed by Churchwell (1999) and Henning et al. (2000). The accretion scenario also leads to a new concept for the maximum stellar mass.

  2. Magnetized Accretion-Ejection Structures

    NASA Astrophysics Data System (ADS)

    Ferreira, Jonathan

    1994-09-01

    For both active galactic nuclei (AGN) and young stellar objects (YSO), the common belief is growing that there is an interdependency between accretion of mass onto a central object and the highly collimated jets. This thesis deals with the investigation of the physical mechanism that leads to the formation of jets from a magnetized accretion disk. This has been done by solving the set of magnetohydrodynamical (MHD) equations in the case of an isothermal disk, using a self-similar approach. All the dynamical terms are included, so that the main results are independant of the modelling and thus, completely general. Indeed, a different temperature vertical profile only slightly modifies the parameters required for stationarity. A resistive thin accretion disk is thread by open magnetic field lines, sheared by its differential rotation. The field lines brake the disk and extract both angular momentum and mechanical energy from it. Because of the large magnetic "lever arm" acting on the disk, the magnetic braking is always dominant and the viscous torque is negligible. An equipartition magnetic field is enough, without significantly perturbing the Keplerian rotation. Thus, jets carry away all the angular momentum of the underlying accretion disk. Steady state accretion is achieved in the disk due to an anomalous magnetic diffusivity that allows the matter to slip across the field lines. This anomalous transport coefficient should arise from the saturation of a strong magnetic instability triggered in the disk. Ambipolar diffusion, which could have been used without losing the generality of the present results, remains however smaller than this anomalous diffusivity in the inner parts of a circumstellar disk. It has been found that steady state ejection can be achieved only if the magnetic torque changes its sign at the disk surface. From this point on, the field lines accelerate azimuthaly the matter transfering it both angular momentum and energy. This requires a

  3. The influence of fallback discs on the spectral and timing properties of neutron stars

    NASA Astrophysics Data System (ADS)

    Yan, T.; Perna, R.; Soria, R.

    2012-07-01

    Fallback discs around neutron stars (NSs) are believed to be an expected outcome of supernova explosions. Here we investigate the consequences of such a common outcome for the timing and spectral properties of the associated NS population, using Monte Carlo population synthesis models. We find that the long-term torque exerted by the fallback disc can substantially influence the late-time period distribution, but with quantitative differences which depend on whether the initial spin distribution is dominated by slow or fast pulsars. For the latter, a single-peaked initial spin distribution becomes bimodal at later times. Timing ages tend to underestimate the real age of older pulsars, and overestimate the age of younger ones. Braking indices cluster in the range 1.5 ≲n≲ 3 for slow-born pulsars, and -0.5 ≲n≲ 5 for fast-born pulsars, with the younger objects found predominantly below n≲ 3. Large values of n, while not common, are possible, and associated with torque transitions in the NS+disc system. The 0.1-10 keV thermal luminosity of the NS+disc system is found to be generally dominated by the disc emission at early times, ? yr, but this declines faster than the thermal surface emission of the NS. Depending on the initial parameters, there can be occasional periods in which some NSs switch from the propeller to the accretion phase, increasing their luminosity up to the Eddington limit for ˜103-104 years.

  4. A Theoretical Perspective on the Formation and Fragmentation of Protostellar Discs

    NASA Astrophysics Data System (ADS)

    Whitworth, A.; Lomax, O.

    2016-01-01

    We discuss the factors influencing the formation and gravitational fragmentation of protostellar discs. We start with a review of how observations of prestellar cores can be analysed statistically to yield plausible initial conditions for simulations of their subsequent collapse. Simulations based on these initial conditions show that, despite the low levels of turbulence in prestellar cores, they deliver primary protostars and associated discs which are routinely subject to stochastic impulsive perturbations; consequently misalignment of the spins and orbits of protostars are common. Also, the simulations produce protostars that collectively have a mass function and binary statistics matching those observed in nearby star-formation regions, but only if a significant fraction of the turbulent energy in the core is solenoidal, and accretion onto the primary protostar is episodic with a duty cycle ≳ 3 000 yr. Under this circumstance, a core typically spawns between 4 and 5 protostars, with high efficiency, and the lower mass protostars are mainly formed by disc fragmentation. The requirement that a proto-fragment in a disc lose thermal energy on a dynamical timescale dictates that there is a sweet spot for disc fragmentation at radii 70 AU ≲ R ≲ 100 AU and temperatures 10 K ≲ T ≲ 20 K, and this might explain the brown dwarf desert.

  5. Sadness is unique: neural processing of emotions in speech prosody in musicians and non-musicians.

    PubMed

    Park, Mona; Gutyrchik, Evgeny; Welker, Lorenz; Carl, Petra; Pöppel, Ernst; Zaytseva, Yuliya; Meindl, Thomas; Blautzik, Janusch; Reiser, Maximilian; Bao, Yan

    2014-01-01

    Musical training has been shown to have positive effects on several aspects of speech processing, however, the effects of musical training on the neural processing of speech prosody conveying distinct emotions are yet to be better understood. We used functional magnetic resonance imaging (fMRI) to investigate whether the neural responses to speech prosody conveying happiness, sadness, and fear differ between musicians and non-musicians. Differences in processing of emotional speech prosody between the two groups were only observed when sadness was expressed. Musicians showed increased activation in the middle frontal gyrus, the anterior medial prefrontal cortex, the posterior cingulate cortex and the retrosplenial cortex. Our results suggest an increased sensitivity of emotional processing in musicians with respect to sadness expressed in speech, possibly reflecting empathic processes.

  6. Identity recognition and happy and sad facial expression recall: influence of depressive symptoms.

    PubMed

    Jermann, Françoise; van der Linden, Martial; D'Argembeau, Arnaud

    2008-05-01

    Relatively few studies have examined memory bias for social stimuli in depression or dysphoria. The aim of this study was to investigate the influence of depressive symptoms on memory for facial information. A total of 234 participants completed the Beck Depression Inventory II and a task examining memory for facial identity and expression of happy and sad faces. For both facial identity and expression, the recollective experience was measured with the Remember/Know/Guess procedure (Gardiner & Richardson-Klavehn, 2000). The results show no major association between depressive symptoms and memory for identities. However, dysphoric individuals consciously recalled (Remember responses) more sad facial expressions than non-dysphoric individuals. These findings suggest that sad facial expressions led to more elaborate encoding, and thereby better recollection, in dysphoric individuals. PMID:18432481

  7. Sadness is unique: neural processing of emotions in speech prosody in musicians and non-musicians

    PubMed Central

    Park, Mona; Gutyrchik, Evgeny; Welker, Lorenz; Carl, Petra; Pöppel, Ernst; Zaytseva, Yuliya; Meindl, Thomas; Blautzik, Janusch; Reiser, Maximilian; Bao, Yan

    2015-01-01

    Musical training has been shown to have positive effects on several aspects of speech processing, however, the effects of musical training on the neural processing of speech prosody conveying distinct emotions are yet to be better understood. We used functional magnetic resonance imaging (fMRI) to investigate whether the neural responses to speech prosody conveying happiness, sadness, and fear differ between musicians and non-musicians. Differences in processing of emotional speech prosody between the two groups were only observed when sadness was expressed. Musicians showed increased activation in the middle frontal gyrus, the anterior medial prefrontal cortex, the posterior cingulate cortex and the retrosplenial cortex. Our results suggest an increased sensitivity of emotional processing in musicians with respect to sadness expressed in speech, possibly reflecting empathic processes. PMID:25688196

  8. Mood and heuristics: the influence of happy and sad states on sensitivity and bias in stereotyping.

    PubMed

    Park, J; Banaji, M R

    2000-06-01

    The influence of mood states on the propensity to use heuristics as expressed in stereotypes was examined using signal detection statistics. Participants experienced happy, neutral, or sad moods and "remembered" whether names connoting race (African American, European American) belonged to social categories (criminal, politician, basketball player). Positive mood increased reliance on heuristics, indexed by higher false identification of members of stereotyped groups. Positive mood lowered sensitivity (d'), even among relative experts, and shifted bias (beta) or criterion to be more lenient for stereotypical names. In contrast, sad mood did not disrupt sensitivity and, in fact, revealed the use of a stricter criterion compared with baseline mood. Results support theories that characterize happy mood as a mental state that predisposes reliance on heuristics and sad mood as dampening such reliance.

  9. Formation of massive stars by growing accretion

    NASA Astrophysics Data System (ADS)

    Maeder, André

    We calculate pre-main sequence evolutionary tracks with accretion rates growing with the actual stellar masses. We show that accretion rates growing at least as M1.5 are necessary to fit the constraints on the lifetimes and HR diagram. Most interestingly, such accretion rates growing with the stellar mass well correspond to those derived from observations of mass outflows (Churchwell 2000; Henning et al. 2000). These rates also lie in the permitted region of the dynamical models.

  10. Lithium synthesis in microquasar accretion.

    PubMed

    Iocco, Fabio; Pato, Miguel

    2012-07-13

    We study the synthesis of lithium isotopes in the hot tori formed around stellar mass black holes by accretion of the companion star. We find that sizable amounts of both stable isotopes 6Li and 7Li can be produced, the exact figures varying with the characteristics of the torus and reaching as much as 10(-2) M⊙ for each isotope. This mass output is enough to contaminate the entire Galaxy at a level comparable with the original, pregalactic amount of lithium and to overcome other sources such as cosmic-ray spallation or stellar nucleosynthesis. PMID:23030150

  11. Lithium synthesis in microquasar accretion.

    PubMed

    Iocco, Fabio; Pato, Miguel

    2012-07-13

    We study the synthesis of lithium isotopes in the hot tori formed around stellar mass black holes by accretion of the companion star. We find that sizable amounts of both stable isotopes 6Li and 7Li can be produced, the exact figures varying with the characteristics of the torus and reaching as much as 10(-2) M⊙ for each isotope. This mass output is enough to contaminate the entire Galaxy at a level comparable with the original, pregalactic amount of lithium and to overcome other sources such as cosmic-ray spallation or stellar nucleosynthesis.

  12. [Exploration on Electroencephalogram Mechanism Differences of Negative Emotions Induced by Disgusted and Sad Situation Images].

    PubMed

    Wang, Xin; Jin, Jingna; Li, Song; Liu, Zhipeng; Yin, Tao

    2015-12-01

    Evolutionary psychology holds such an opinion that negative situation may threaten survival, trigger avoidance motive and have poor effects on the human-body function and the psychological quality. Both disgusted and sad situations can induce negative emotions. However, differences between the two situations on attention capture and emotion cognition during the emotion induction are still not well known. Typical disgusted and sad situation images were used in the present study to induce two negative emotions, and 15 young students (7 males and 8 females, aged 27 ± 3) were recruited in the experiments. Electroencephalogram of 32 leads was recorded when the subjects were viewing situation images, and event-related potentials (ERP) of all leads were obtained for future analysis. Paired sample t tests were carried out on two ERP signals separately induced by disgusted and sad situation images to get time quantum with significant statistical differences between the two ERP signals. Root-mean-square deviations of two ERP signals during each time quantum were calculated and the brain topographic map based on root-mean-square deviations was drawn to display differences of two ERP signals in spatial. Results showed that differences of ERP signals induced by disgusted and sad situation images were mainly manifested in T1 (120-450 ms) early and T2 (800-1,000 ms) later. During the period of T1, the occipital lobe reflecting attention capture was activated by both disgusted and sad situation images, but the prefrontal cortex reflecting emotion sense was activated only by disgusted situation images. During the period of T2, the prefrontal cortex was activated by both disgusted and sad situation images. However, the parietal lobe was activated only by disgusted situation images, which showed stronger emotional perception. The research results would have enlightenment to deepen understanding of negative emotion and to exploredeep cognitive neuroscience mechanisms of negative

  13. Impact of civil war on emotion recognition: the denial of sadness in Sierra Leone

    PubMed Central

    Umiltà, Maria Allessandra; Wood, Rachel; Loffredo, Francesca; Ravera, Roberto; Gallese, Vittorio

    2013-01-01

    Studies of children with atypical emotional experience demonstrate that childhood exposure to high levels of hostility and threat biases emotion perception. This study investigates emotion processing, in former child soldiers and non-combatant civilians. All participants have experienced prolonged violence exposure during childhood. The study, carried out in Sierra Leone, aimed to examine the effects of exposure to and forced participation in acts of extreme violence on the emotion processing of young adults war survivors. A total of 76 young, male adults (38 former child soldier survivors and 38 civilian survivors) were tested in order to assess participants' ability to identify four different facial emotion expressions from photographs and movies. Both groups were able to recognize facial expressions of emotion. However, despite their general ability to correctly identify facial emotions, participants showed a significant response bias in their recognition of sadness. Both former soldiers and civilians made more errors in identifying expressions of sadness than in the other three emotions and when mislabeling sadness participants most often described it as anger. Conversely, when making erroneous identifications of other emotions, participants were most likely to label the expressed emotion as sadness. In addition, while for three of the four emotions participants were better able to make a correct identification the greater the intensity of the expression, this pattern was not observed for sadness. During movies presentation the recognition of sadness was significantly worse for soldiers. While both former child soldiers and civilians were found to be able to identify facial emotions, a significant response bias in their attribution of negative emotions was observed. Such bias was particularly pronounced in former child soldiers. These findings point to a pervasive long-lasting effect of childhood exposure to violence on emotion processing in later life. PMID

  14. 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.

  15. 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.

  16. 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.

  17. Accretion flows govern black hole jet properties

    NASA Astrophysics Data System (ADS)

    Koljonen, K.; Russell, D.; Fernández Ontiveros, J.; Miller-Jones, J.; Russell, T.; Curran, P.; Soria, R.; Markoff, S.; van der Horst, A.; Casella, P.

    2015-07-01

    The process of jet formation in accreting black holes, and the conditions under which it occurs is currently hotly debated, with competing models predicting the jet power to be governed by black hole spin, the magnetic field strength, the location of the jet base, the mass accretion rate and/or the properties of the inner accretion flow. We present new results that show empirical correlations between the accretion flow properties and the spectral energy distribution of the jets launched from accreting black holes. The X-ray power law is directly related to the particle energy distribution in the hot accretion flow. We find that the photon index of this power law correlates with the characteristic break frequency in the jet spectrum emitted near the jet base, and the jet luminosity up to the break frequency. The observed correlations can be explained by the energy distribution of electrons in the hot accretion flow being subsequently channeled into the jet. These correlations represent a new inflow--outflow connection in accreting black holes, and demonstrate that the spectral properties of the jet rely most critically on the conditions in the inner accretion flow, rather than other parameters such as the black hole mass or spin.

  18. Bondi accretion onto cosmological black holes

    NASA Astrophysics Data System (ADS)

    Karkowski, Janusz; Malec, Edward

    2013-02-01

    In this paper we investigate a steady accretion within the Einstein-Straus vacuole, in the presence of the cosmological constant. The dark energy damps the mass accretion rate and—above a certain limit—completely stops the steady accretion onto black holes, which, in particular, is prohibited in the inflation era and after (roughly) 1012 years from the big bang (assuming the presently known value of the cosmological constant). Steady accretion would not exist in the late phases of the Penrose’s scenario—known as the Weyl curvature hypothesis—of the evolution of the Universe.

  19. Relativistic reverberation in the accretion flow of a Tidal Disruption Event

    NASA Astrophysics Data System (ADS)

    Kara, Erin; Miller, Jon M.; Reynolds, Christopher S.; Dai, Lixin J.

    2016-04-01

    Our current understanding of the curved spacetime around supermassive black holes is based on actively accreting black holes, which make up only ten per cent or less of the overall population. X-ray observations of that small fraction reveal strong gravitational redshifts that indicate that many of these black holes are rapidly rotating, however selection biases suggest that these results of a few are not necessarily reflective of the majority of black hole spins in the Universe. Tidal disruption events, where a star orbiting an otherwise dormant black hole gets tidally shredded and accreted on to the black hole, can provide a short, unbiased glimpse at the spacetime around the other ninety per cent of black holes. Observations of tidal disruptions have hitherto revealed the formation of an accretion disc and the onset of an accretion-powered jet, but have failed to reveal gravitational redshifts from innermost regions close to the event horizon, which enable the measurement of black hole spin. Here, we report observations of reverberation arising from photons from highly ionized iron (from K shell electrons) reflected off the accretion flow in a tidal disruption event. The asymmetric iron line profile indicates that we are seeing a region close to the event horizon of the black hole, where gravitational redshifts are strong. From the reverberation time delay, we estimate the mass of the central black hole to be a few million solar masses. Combined with the observed luminosity, we conclude the tidal disruption event is accreting at least 100 times the Eddington limit, which is consistent with predictions of the mass fallback rate of a tidally disrupted star. The detection of reverberation from the relativistic depths of this rare hyper-Eddington event demonstrates that the X-rays do not arise from the relativistically moving regions of a jet, as previously thought.

  20. Rapid variability as a probe of warped space-time around accreting black holes

    NASA Astrophysics Data System (ADS)

    Axelsson, Magnus

    2016-07-01

    The geometry of the inner accretion flow of X-ray binaries is complex, with multiple regions contributing to the observed emission. Frequency-resolved spectroscopy is a powerful tool in breaking this spectral degeneracy. We have extracted the spectra of the strong low-frequency quasi-periodic oscillation (QPO) and its harmonic in GX339-4 and XTE J1550-564, and compare these to the time-averaged spectrum and the spectrum of the rapid (<0.1 s) variability. Our results support the picture where the QPO arises from vertical (Lense-Thirring) precession of an inhomogeneous hot flow, softer at larger radii closer to the truncated disc and harder in the innermost parts where the rapid variability is produced. This coupling between variability and spectra allows us to constrain the soft Comptonization component, breaking the degeneracy plaguing the time-averaged spectrum and revealing the geometry of the accretion flow close to the black hole.

  1. Particle dynamics in discs with turbulence generated by the vertical shear instability

    NASA Astrophysics Data System (ADS)

    Stoll, Moritz H. R.; Kley, Wilhelm

    2016-10-01

    Context. Among the candidates for generating turbulence in accretion discs in situations with low intrinsic ionization, the vertical shear instability (VSI) has become an interesting candidate, since it relies purely on a vertical gradient in the angular velocity. Existing numerical simulations have shown that α-values a few times 10-4 can be generated. Aims: The particle growth in the early planet formation phase is determined by the dynamics of embedded dust particles. Here, we address, in particular, the efficiency of VSI-turbulence in concentrating particles to generate overdensities and low collision velocities. Methods: We perform three-dimensional (3D) numerical hydrodynamical simulations of accretion discs around young stars that include radiative transport and irradiation from the central star. The motion of embedded particles within a size range of a fraction of mm up to several m is followed using standard drag formula. Results: We confirm that, under realistic conditions, the VSI is able to generate turbulence in full 3D protoplanetary discs. The irradiated disc shows turbulence within 10 to 60 au. The mean radial motion of the gas is such that it is directed inward near the midplane and outward in the surface layers. We find that large particles drift inward with the expected speed, while small particles can experience phases of outward drift. Additionally, the particles show bunching behaviour with overdensities reaching five times the average value, which is strongest for dimensionless stopping times around unity. Conclusions: Particles in a VSI-turbulent discs are concentrated in large-scale turbulent eddies and show low relative speeds that allow for growing collisions. The reached overdensities will also enable the onset of streaming instabilities, further enhancing particle growth. The outward drift for small particles at higher disk elevations enable the transport of processed high temperature material in the solar system to greater distances.

  2. Shock vaporization and the accretion of the icy satellites of Jupiter and Saturn

    NASA Technical Reports Server (NTRS)

    Ahrens, T. J.; Okeefe, J. D.

    1984-01-01

    The role of impact vaporization acting during the formation of the Jovian and Saturnian satellites is examined in an attempt to explain the observed density in terms of composition of these rock and ice objects. A hypothesis is examined which states that the smaller satellites of Saturn having mean densities in the 1.1 to 1.4 Mg/cu m range represent primordial accreted planetesimal condensates formed in the proto-Jovian and Saturnian accretionary planetary discs. These densities are in the range expected for water-ice/silicate mixtures constrained in the solar values of O/Si and O/Mg atomic ratios. It is demonstrated that if the large satellites accreted from the same group of planetesimals which formed the small Saturnian satellites impact vaporization of water upon accretion in a porous regolith, at low H2O partial pressure, can account for the increase in mean planetesimal density from 1.6 Mg/cu m (43% H2O + 57% silicate) to a mean planetary density of 1.9 Mg/cu m for Ganymedean-sized water silicate objects. If impact volatilization of initially porous planetesimals is assumed, it can be demonstrated starting with planetesimals composed of 54% H2O and 40% silicate partial devolatilization upon accretion will yield a Ganymede-sized planet, having a radius of 2600 km and a density of 1.85 kg/cu m, similar to that of Ganymede, Callisto, and Titan.

  3. New Insights on the Accretion Disk-Winds Connection in Radio-Loud AGNs from Suzaku

    NASA Technical Reports Server (NTRS)

    Tombesi, F.; Sambruna, R. M.; Reeves, J. N.; Braito, V.; Cappi, M.; Reynolds, S.; Mushotzky, R. F.

    2011-01-01

    From the spectral analysis of long Suzaku observations of five radio-loud AGNs we have been able to discover the presence of ultra-fast outflows with velocities ,,approx.0.1 c in three of them, namely 3C III, 3C 120 and 3C 390.3. They are consistent with being accretion disk winds/outflows. We also performed a follow-up on 3C III to monitor its outflow on approx.7 days time-scales and detected an anti-correlated variability of a possible relativistic emission line with respect to blue-shifted Fe K features, following a flux increase. This provides the first direct evidence for an accretion disc-wind connection in an AGN. The mass outflow rate of these outflows can be comparable to the accretion rate and their mechanical power can correspond to a significant fraction of the bolometric luminosity and is comparable to their typical jet power. Therefore, they can possibly play a significant role in the expected feedback from AGNs and can give us further clues on the relation between the accretion disk and the formation of winds/jets.

  4. Swept wing ice accretion modeling

    NASA Technical Reports Server (NTRS)

    Potapczuk, Mark G.; Bidwell, Colin S.

    1990-01-01

    An effort to develop a three-dimensional modeling method was initiated. This first step towards creation of a complete aircraft icing simulation code builds on previously developed methods for calculating three-dimensional flow fields and particle trajectories combined with a two-dimensional ice accretion calculation along coordinate locations corresponding to streamlines. This work is a demonstration of the types of calculations necessary to predict a three-dimensional ice accretion. Results of calculations using the 3-D method for a MS-317 swept wing geometry are projected onto a 2-D plane normal to the wing leading edge and compared to 2-D results for the same geometry. It is anticipated that many modifications will be made to this approach, however, this effort will lay the groundwork for future modeling efforts. Results indicate that the flow field 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 3-D calculation.

  5. 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.

  6. 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.

  7. Time evolution of accreting magnetofluid around a compact object-Newtonian analysis

    NASA Astrophysics Data System (ADS)

    Habibi, Fahimeh; Shaghaghian, Mahboobeh; Pazhouhesh, Reza

    2015-07-01

    Time evolution of a thick disc with finite conductivity around a nonrotating compact object is presented. Along with the Maxwell equations and the Ohm's law, the Newtonian limit of the relativistic fluid equations governing the motion of a finitely conducting plasma is derived. The magnetofluid is considered to possess only the poloidal components of the electromagnetic field. Moreover, the shear viscous stress is neglected, as well as the self-gravity of the disc. In order to solve the equations, we have used a self-similar solution. The main features of this solution are as follows. The azimuthal velocity is somewhat increased from the Keplerian value in the equator plane to the super-Keplerian values at the surface of disc. Moreover, the radial velocity is obtained proportional to the meridional velocity. Magnetofluid does not have any nonzero component of the current density. Subsequently, the electromagnetic force is vanished and does not play any role in the force balance. While the pressure gradient maintains the disc structure in latitudinal direction, magnetofluid has no accretion on the central compact object. Analogously to the parameter α in the standard model, our calculations contain one parameter η0 which specifies the size of the electrical resistivity.

  8. Disc reflection and a possible disc wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9-342058

    NASA Astrophysics Data System (ADS)

    Degenaar, N.; Altamirano, D.; Parker, M.; Miller-Jones, J. C. A.; Miller, J. M.; Heinke, C. O.; Wijnands, R.; Ludlam, R.; Parikh, A.; Hessels, J. W. T.; Gusinskaia, N.; Deller, A. T.; Fabian, A. C.

    2016-10-01

    1RXS J180408.9-342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present NuSTAR, Swift, and Chandra observations obtained around the peak brightness of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of LX ≃ (2-3) × 1037(D/5.8 kpc)2 erg s-1 (0.5-10 keV). The NuSTAR data reveal a broad Fe-K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disc is viewed at an inclination of i ≃ 27°-35° and extended close to the neutron star, down to Rin ≃ 5-7.5 gravitational radii (≃11-17 km). This inner disc radius suggests that the neutron star magnetic field strength is B ≲ 2 × 108 G. We find a narrow absorption line in the Chandra/HEG data at an energy of ≃7.64 keV with a significance of ≃4.8σ. This feature could correspond to blueshifted Fe XXVI and arise from an accretion disc wind, which would imply an outflow velocity of vout ≃ 0.086c (≃25 800 km s-1). However, this would be extreme for an X-ray binary and it is unclear if a disc wind should be visible at the low inclination angle that we infer from our reflection analysis. Finally, we discuss how the X-ray and optical properties of 1RXS J180408.9-342058 are consistent with a relatively small (Porb ≲ 3 h) binary orbit.

  9. Growing massive black holes through supercritical accretion of stellar-mass seeds

    NASA Astrophysics Data System (ADS)

    Lupi, A.; Haardt, F.; Dotti, M.; Fiacconi, D.; Mayer, L.; Madau, P.

    2016-03-01

    The rapid assembly of the massive black holes that power the luminous quasars observed at z ˜ 6-7 remains a puzzle. Various direct collapse models have been proposed to head-start black hole growth from initial seeds with masses ˜105 M⊙, which can then reach a billion solar mass while accreting at the Eddington limit. Here, we propose an alternative scenario based on radiatively inefficient supercritical accretion of stellar-mass holes embedded in the gaseous circumnuclear discs (CNDs) expected to exist in the cores of high-redshift galaxies. Our sub-pc resolution hydrodynamical simulations show that stellar-mass holes orbiting within the central 100 pc of the CND bind to very high density gas clumps that arise from the fragmentation of the surrounding gas. Owing to the large reservoir of dense cold gas available, a stellar-mass black hole allowed to grow at super-Eddington rates according to the `slim-disc' solution can increase its mass by three orders of magnitudes within a few million years. These findings are supported by simulations run with two different hydro codes, RAMSES based on the Adaptive Mesh Refinement technique and GIZMO based on a new Lagrangian Godunov-type method, and with similar, but not identical, sub-grid recipes for star formation, supernova feedback, black hole accretion and feedback. The low radiative efficiency of supercritical accretion flows are instrumental to the rapid mass growth of our black holes, as they imply modest radiative heating of the surrounding nuclear environment.

  10. Remarkable spectral variability on the spin period of the accreting white dwarf in V455 And

    NASA Astrophysics Data System (ADS)

    Bloemen, S.; Steeghs, D.; De Smedt, K.; Vos, J.; Gänsicke, B. T.; Marsh, T. R.; Rodriguez-Gil, P.

    2013-03-01

    We present spin-resolved spectroscopy of the accreting white dwarf binary V455 And. With a suggested spin period of only 67 s, it has one of the fastest spinning white dwarfs known. To study the spectral variability on the spin period of the white dwarf, we observed V455 And with 2 s integration times, which is significantly shorter than the spin rate of the white dwarf. To achieve this cadence, we used the blue arm of the ISIS spectrograph at the 4.2-m William Herschel Telescope, equipped with an electron multiplying CCD (EMCCD). Strong coherent signals were detected in our time series, which led to a robust determination of the spin period of the white dwarf (Pspin = 67.619 ± 0.002 s). Folding the spectra on the white dwarf spin period uncovered very complex emission line variations in Hγ, He I λ4472 and He II λ4686. We attribute the observed spin phase dependence of the emission line shape to the presence of magnetically controlled accretion on to the white dwarf via accretion curtains, consistent with an intermediate polar type system. We are, however, not aware of any specific model that can quantitatively explain the complex velocity variations we detect in our observations. The orbital variations in the spectral lines indicate that the accretion disc of V455 And is rather structureless, contrary to the disc of the prototype of the intermediate polars, DQ Her. This work demonstrates the potential of EMCCDs to observe faint targets at high cadence, as readout noise would make such a study impossible with conventional CCDs.

  11. Electromagnetic Levitation of a Disc

    ERIC Educational Resources Information Center

    Valle, R.; Neves, F.; de Andrade, R., Jr.; Stephan, R. M.

    2012-01-01

    This paper presents a teaching experiment that explores the levitation of a disc of ferromagnetic material in the presence of the magnetic field produced by a single electromagnet. In comparison to the classical experiment of the levitation of a sphere, the main advantage of the proposed laboratory bench is that the uniform magnetic field…

  12. Optical Disc Applications in Libraries.

    ERIC Educational Resources Information Center

    Andre, Pamela Q. J.

    1989-01-01

    Discusses a variety of library applications of optical disc storage technology, including CD-ROM, digital videodisc, and WORM. Research and development projects at the Library of Congress, National Library of Medicine, and National Agricultural Library are described, products offered by library networks are reviewed, and activities in academic and…

  13. A disc corona-jet model for the radio/X-ray correlation in black hole X-ray binaries

    NASA Astrophysics Data System (ADS)

    Qiao, Erlin; Liu, B. F.

    2015-04-01

    The observed tight radio/X-ray correlation in the low spectral state of some black hole X-ray binaries implies the strong coupling of the accretion and jet. The correlation of L_R ∝ L_X^{˜ 0.5-0.7} was well explained by the coupling of a radiatively inefficient accretion flow and a jet. Recently, however, a growing number of sources show more complicated radio/X-ray correlations, e.g. L_R ∝ L_X^{˜ 1.4} for LX/LEdd ≳ 10-3, which is suggested to be explained by the coupling of a radiatively efficient accretion flow and a jet. In this work, we interpret the deviation from the initial radio/X-ray correlation for LX/LEdd ≳ 10-3 with a detailed disc corona-jet model. In this model, the disc and corona are radiatively and dynamically coupled. Assuming a fraction of the matter in the accretion flow, η ≡ dot{M}_jet/dot{M}, is ejected to form the jet, we can calculate the emergent spectrum of the disc corona-jet system. We calculate LR and LX at different dot{M}, adjusting η to fit the observed radio/X-ray correlation of the black hole X-ray transient H1743-322 for LX/LEdd > 10-3. It is found that always the X-ray emission is dominated by the disc corona and the radio emission is dominated by the jet. We noted that the value of η for the deviated radio/X-ray correlation for LX/LEdd > 10-3 is systematically less than that of the case for LX/LEdd < 10-3, which is consistent with the general idea that the jet is often relatively suppressed at the high-luminosity phase in black hole X-ray binaries.

  14. The collimation of magnetic jets by disc winds

    NASA Astrophysics Data System (ADS)

    Globus, N.; Levinson, A.

    2016-09-01

    The collimation of a Poynting-flux dominated jet by a wind emanating from the surface of an accretion flow is computed using a semi-analytic model. The injection of the disc wind is treated as a boundary condition in the equatorial plane, and its evolution is followed by invoking a prescribed geometry of streamlines. Solutions are obtained for a wide range of disc wind parameters. It is found that jet collimation generally occurs when the total wind power exceeds about 10 percents of the jet power. For moderate wind powers, we find gradual collimation. For strong winds, we find rapid collimation followed by focusing of the jet, after which it remains narrow over many Alfvén crossing times before becoming conical. We estimate that in the later case, the jet's magnetic field may be dissipated by the current-driven kink instability over a distance of a few hundreds gravitational radii. We apply the model to M87 and show that the observed parabolic shape of the radio jet within the Bondi radius can be reproduced provided that the wind injection zone extends to several hundreds gravitational radii, and that its total power is about one-third of the jet power. The radio spectrum can be produced by synchrotron radiation of relativistically hot, thermal electrons in the sheath flow surrounding the inner jet.

  15. The Smad4 activation domain (SAD) is a proline-rich, p300-dependent transcriptional activation domain.

    PubMed

    de Caestecker, M P; Yahata, T; Wang, D; Parks, W T; Huang, S; Hill, C S; Shioda, T; Roberts, A B; Lechleider, R J

    2000-01-21

    Transforming growth factor-beta (TGF-beta) family members signal through a unique set of intracellular proteins called Smads. Smad4, previously identified as the tumor suppressor DPC4, is functionally distinct among the Smad family, and is required for the assembly and transcriptional activation of diverse, Smad-DNA complexes. We previously identified a 48-amino acid proline-rich regulatory element within the middle linker domain of this molecule, the Smad4 activation domain (SAD), which is essential for mediating these signaling activities. We now characterize the functional activity of the SAD. Mutants lacking the SAD are still able to form complexes with other Smad family members and associated transcription factors, but cannot activate transcription in these complexes. Furthermore, the SAD itself is able to activate transcription in heterologous reporter assays, identifying it as a proline-rich transcriptional activation domain, and indicating that the SAD is both necessary and sufficient to activate Smad-dependent transcriptional responses. We show that transcriptional activation by the SAD is p300-dependent, and demonstrate that this activity is associated with a physical interaction of the SAD with the amino terminus of p300. These data identify a novel function of the middle linker region of Smad4, and define the role of the SAD as an important locus determining the transcriptional activation of the Smad complex.

  16. Influence of trait empathy on the emotion evoked by sad music and on the preference for it

    PubMed Central

    Kawakami, Ai; Katahira, Kenji

    2015-01-01

    Some people experience pleasant emotion when listening to sad music. Therefore, they can enjoy listening to it. In the current study, we aimed to investigate such apparently paradoxical emotional mechanisms and focused on the influence of individuals’ trait empathy, which has been reported to associate with emotional responses to sad music and a preference for it. Eighty-four elementary school children (42 males and 42 females, mean age 11.9 years) listened to two kinds of sad music and rated their emotional state and liking toward them. In addition, trait empathy was assessed using the Interpersonal Reactivity Index scale, which comprises four sub-components: Empathic Concern, Personal Distress, Perspective Taking, and Fantasy (FS). We conducted a path analysis and tested our proposed model that hypothesized that trait empathy and its sub-components would affect the preference for sad music directly or indirectly, mediated by the emotional response to the sad music. Our findings indicated that FS, a sub-component of trait empathy, was directly associated with liking sad music. Additionally, perspective taking ability, another sub-component of trait empathy, was correlated with the emotional response to sad music. Furthermore, the experience of pleasant emotions contributed to liking sad music. PMID:26578992

  17. Influence of trait empathy on the emotion evoked by sad music and on the preference for it.

    PubMed

    Kawakami, Ai; Katahira, Kenji

    2015-01-01

    Some people experience pleasant emotion when listening to sad music. Therefore, they can enjoy listening to it. In the current study, we aimed to investigate such apparently paradoxical emotional mechanisms and focused on the influence of individuals' trait empathy, which has been reported to associate with emotional responses to sad music and a preference for it. Eighty-four elementary school children (42 males and 42 females, mean age 11.9 years) listened to two kinds of sad music and rated their emotional state and liking toward them. In addition, trait empathy was assessed using the Interpersonal Reactivity Index scale, which comprises four sub-components: Empathic Concern, Personal Distress, Perspective Taking, and Fantasy (FS). We conducted a path analysis and tested our proposed model that hypothesized that trait empathy and its sub-components would affect the preference for sad music directly or indirectly, mediated by the emotional response to the sad music. Our findings indicated that FS, a sub-component of trait empathy, was directly associated with liking sad music. Additionally, perspective taking ability, another sub-component of trait empathy, was correlated with the emotional response to sad music. Furthermore, the experience of pleasant emotions contributed to liking sad music. PMID:26578992

  18. Maternal Sadness and Adolescents' Responses to Stress in Offspring of Mothers with and without a History of Depression

    ERIC Educational Resources Information Center

    Jaser, Sarah S.; Fear, Jessica M.; Reeslund, Kristen L.; Champion, Jennifer E.; Reising, Michelle M.; Compas, Bruce E.

    2008-01-01

    This study examined maternal sadness and adolescents' responses to stress in the offspring (n = 72) of mothers with and without a history of depression. Mothers with a history of depression reported higher levels of current depressive symptoms and exhibited greater sadness during interactions with their adolescent children (ages 11-14) than…

  19. Responses to Children's Sadness: Mothers' and Fathers' Unique Contributions and Perceptions

    ERIC Educational Resources Information Center

    Cassano, Michael C.; Zeman, Janice L.; Sanders, Wesley M.

    2014-01-01

    Parental socialization of children's sadness was examined through self-report, spouse report, and a parent-child sadness discussion task. A total of 79 two-parent, predominantly White, middle-class families participated with one child in grades 2-5 (44 sons; M = 9 years, 8 months). Analyses revealed that mothers and fathers respond…

  20. Neural correlates of delicate sadness: an fMRI study based on the neuroaesthetics of Noh masks.

    PubMed

    Osaka, Naoyuki; Minamoto, Takehiro; Yaoi, Ken; Osaka, Mariko

    2012-01-01

    Although the role of the amygdala in processing facial expressions of fear is well established, its role in the processing of other emotions, such as sadness, remains unclear. We hypothesized that the amygdala would respond to a negative emotion such as sadness, when sadness was represented by a theatrical mask. In the traditional Japanese Noh theater, performers use masks to indicate many of the mental states of the characters they portray. Here, we report a functional MRI study, in which participants' brains were scanned while viewing Noh masks, whose faces appeared delicately sad. Among seventy standard Noh masks previously rated by the individual participants, we chose six top-rated sad masks and six neutral masks to study the neural correlates of such delicate sadness. Results based on a region of interest analysis indicated the activation of the right amygdala while viewing sad masks. We suggest the fact that such delicate sad masks could activate the amygdala, and it could possibly be because of an underlying similarity to emotions such as fear and disgust. PMID:22113213

  1. Influence of trait empathy on the emotion evoked by sad music and on the preference for it.

    PubMed

    Kawakami, Ai; Katahira, Kenji

    2015-01-01

    Some people experience pleasant emotion when listening to sad music. Therefore, they can enjoy listening to it. In the current study, we aimed to investigate such apparently paradoxical emotional mechanisms and focused on the influence of individuals' trait empathy, which has been reported to associate with emotional responses to sad music and a preference for it. Eighty-four elementary school children (42 males and 42 females, mean age 11.9 years) listened to two kinds of sad music and rated their emotional state and liking toward them. In addition, trait empathy was assessed using the Interpersonal Reactivity Index scale, which comprises four sub-components: Empathic Concern, Personal Distress, Perspective Taking, and Fantasy (FS). We conducted a path analysis and tested our proposed model that hypothesized that trait empathy and its sub-components would affect the preference for sad music directly or indirectly, mediated by the emotional response to the sad music. Our findings indicated that FS, a sub-component of trait empathy, was directly associated with liking sad music. Additionally, perspective taking ability, another sub-component of trait empathy, was correlated with the emotional response to sad music. Furthermore, the experience of pleasant emotions contributed to liking sad music.

  2. 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. PMID:23283175

  3. 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.

  4. Foundations of Black Hole Accretion Disk Theory

    NASA Astrophysics Data System (ADS)

    Abramowicz, Marek A.; Fragile, P. Chris

    2013-12-01

    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).

  5. On the dynamics of planetesimals embedded in turbulent protoplanetary discs with dead zones

    NASA Astrophysics Data System (ADS)

    Gressel, Oliver; Nelson, Richard P.; Turner, Neal J.

    2011-08-01

    Accretion in protoplanetary discs is thought to be driven by magnetohydrodynamic (MHD) turbulence via the magnetorotational instability. Recent work has shown that a planetesimal swarm embedded in a fully turbulent disc is subject to strong excitation of the velocity dispersion, leading to collisional destruction of bodies with radii Rp < 100 km. Significant diffusion of planetesimal semimajor axes also arises, leading to large-scale spreading of the planetesimal population throughout the inner regions of the protoplanetary disc, in apparent contradiction of constraints provided by the distribution of asteroids within the asteroid belt. In this paper, we examine the dynamics of planetesimals embedded in vertically stratified turbulent discs, with and without dead zones. Our main aims are to examine the turbulent excitation of the velocity dispersion, and the radial diffusion, of planetesimals in these discs. We employ 3D MHD simulations using the shearing box approximation, along with an equilibrium chemistry model that is used to calculate the ionization fraction of the disc gas as a function of time and position. Ionization is assumed to arise because of stellar X-rays, galactic cosmic rays and radioactive nuclei. In agreement with our previous study, we find that planetesimals in fully turbulent discs develop large random velocities that will lead to collisional destruction/erosion for bodies with sizes below 100 km, and undergo radial diffusion on a scale ˜2.5 au over a 5 Myr disc lifetime. But planetesimals in a dead zone experience a much reduced excitation of their random velocities, and equilibrium velocity dispersions lie between the disruption thresholds for weak and strong aggregates for sizes Rp≤ 100 km. We also find that radial diffusion occurs over a much reduced length-scale ˜0.25 au over the disc lifetime, this being consistent with Solar system constraints. We conclude that planetesimal growth via mutual collisions between smaller bodies cannot

  6. 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

  7. Peripheral Disc Margin Shape and Internal Disc Derangement: Imaging Correlation in Significantly Painful Discs Identified at Provocation Lumbar Discography

    PubMed Central

    Bartynski, W.S.; Rothfus, W.E.

    2012-01-01

    Summary Annular margin shape is used to characterize lumbar disc abnormality on CT/MR imaging studies. Abnormal discs also have internal derangement including annular degeneration and radial defects. The purpose of this study was to evaluate potential correlation between disc-margin shape and annular internal derangement on post-discogram CT in significantly painful discs encountered at provocation lumbar discography (PLD). Significantly painful discs were encountered at 126 levels in 86 patients (47 male, 39 female) studied by PLD where no prior surgery had been performed and response to intradiscal lidocaine after provocation resulted in either substantial/total relief or no improvement after lidocaine administration. Post-discogram CT and discogram imaging was evaluated for disc-margin characteristics (bulge/protrusion), features of disc internal derangement (radial annular defect [RD: radial tear/fissure/annular gap], annular degeneration) and presence/absence of discographic contrast leakage. In discs with focal protrusion, 50 of 63 (79%) demonstrated Grade 3 RD with 13 (21%) demonstrating severe degenerative change only. In discs with generalized-bulge-only, 48 of 63 (76%) demonstrated degenerative change only (primarily Dallas Grade 3) with 15 of 63 (24%) demonstrating a RD (Dallas Grade 3). Differences were highly statistically significant (p<0.001). Pain elimination with intra-discal lidocaine correlated with discographic contrast leakage (p<0.001). Disc-margin shape correlates with features of internal derangement in significantly painful discs encountered at PLD. Discs with focal protrusion typically demonstrate RD while generalized bulging discs typically demonstrated degenerative changes only (p<0.001). Disc-margin shape may provide an important imaging clue to the cause of chronic discogenic low back pain. PMID:22681741

  8. Peripheral disc margin shape and internal disc derangement: imaging correlation in significantly painful discs identified at provocation lumbar discography.

    PubMed

    Bartynski, W S; Rothfus, W E

    2012-06-01

    Annular margin shape is used to characterize lumbar disc abnormality on CT/MR imaging studies. Abnormal discs also have internal derangement including annular degeneration and radial defects. The purpose of this study was to evaluate potential correlation between disc-margin shape and annular internal derangement on post-discogram CT in significantly painful discs encountered at provocation lumbar discography (PLD). Significantly painful discs were encountered at 126 levels in 86 patients (47 male, 39 female) studied by PLD where no prior surgery had been performed and response to intradiscal lidocaine after provocation resulted in either substantial/total relief or no improvement after lidocaine administration. Post-discogram CT and discogram imaging was evaluated for disc-margin characteristics (bulge/protrusion), features of disc internal derangement (radial annular defect [RD: radial tear/fissure/annular gap], annular degeneration) and presence/absence of discographic contrast leakage. In discs with focal protrusion, 50 of 63 (79%) demonstrated Grade 3 RD with 13 (21%) demonstrating severe degenerative change only. In discs with generalized-bulge-only, 48 of 63 (76%) demonstrated degenerative change only (primarily Dallas Grade 3) with 15 of 63 (24%) demonstrating a RD (Dallas Grade 3). Differences were highly statistically significant (p<0.001). Pain elimination with intra-discal lidocaine correlated with discographic contrast leakage (p<0.001). Disc-margin shape correlates with features of internal derangement in significantly painful discs encountered at PLD. Discs with focal protrusion typically demonstrate RD while generalized bulging discs typically demonstrated degenerative changes only (p<0.001). Disc-margin shape may provide an important imaging clue to the cause of chronic discogenic low back pain. PMID:22681741

  9. On emotion-cognition integration: The effect of happy and sad moods on language comprehension.

    PubMed

    Egidi, Giovanna

    2015-01-01

    I comment on Pessoa's (2013) idea that the interaction between emotion and cognition cannot be reduced to mutual interference. As an example that bolsters Pessoa's position, I discuss the effects of happy and sad moods on discourse and sentence comprehension. I distinguish between the effects of moods elicited without participants' knowledge (incidental) and moods elicited with participants' contribution (constructed). PMID:26786957

  10. Sad and happy emotion discrimination in music by children with cochlear implants.

    PubMed

    Hopyan, Talar; Manno, Francis A M; Papsin, Blake C; Gordon, Karen A

    2016-01-01

    Children using cochlear implants (CIs) develop speech perception but have difficulty perceiving complex acoustic signals. Mode and tempo are the two components used to recognize emotion in music. Based on CI limitations, we hypothesized children using CIs would have impaired perception of mode cues relative to their normal hearing peers and would rely more heavily on tempo cues to distinguish happy from sad music. Study participants were children with 13 right CIs and 3 left CIs (M = 12.7, SD = 2.6 years) and 16 normal hearing peers. Participants judged 96 brief piano excerpts from the classical genre as happy or sad in a forced-choice task. Music was randomly presented with alterations of transposed mode, tempo, or both. When music was presented in original form, children using CIs discriminated between happy and sad music with accuracy well above chance levels (87.5%) but significantly below those with normal hearing (98%). The CI group primarily used tempo cues, whereas normal hearing children relied more on mode cues. Transposing both mode and tempo cues in the same musical excerpt obliterated cues to emotion for both groups. Children using CIs showed significantly slower response times across all conditions. Children using CIs use tempo cues to discriminate happy versus sad music reflecting a very different hearing strategy than their normal hearing peers. Slower reaction times by children using CIs indicate that they found the task more difficult and support the possibility that they require different strategies to process emotion in music than normal.

  11. Scaffolding Young Children's Prosocial Responsiveness: Preschoolers' Responses to Adult Sadness, Anger, and Pain.

    ERIC Educational Resources Information Center

    Denham, Susanne A.; And Others

    Two studies investigated children's responsiveness to an adult's negative emotions (anger, sadness, and pain). The studies also evaluated effects of adult scaffolding (labeling and explaining negative emotions, and requesting help). In the first study, subjects were 55 preschool children between the ages of 33 and 56 months. During individual play…

  12. Parental Personality and Its Relationship to Socialization of Sadness in Children.

    ERIC Educational Resources Information Center

    Race, Eleanor; Brand, Ann E.

    The relationship between parental personality traits and how parents socialize their children's emotions is largely unexplored. This study examined the association of personality traits such as Neuroticism and Agreeableness, and emotion traits such as Anxiety and Trait Depression to the strategies parents use to socialize their children's sadness,…

  13. Relations among Sadness Regulation, Peer Acceptance, and Social Functioning in Early Adolescence: The Role of Gender

    ERIC Educational Resources Information Center

    Perry-Parrish, Carisa; Zeman, Janice

    2011-01-01

    Using a multi-informant approach, this study examined emotion regulation within the social context of White and Black adolescent peer groups by assessing two aspects of sadness expression management (i.e., inhibition, disinhibition) and their linkages to peer acceptance and social functioning as a function of gender and ethnicity. Seventh- and…

  14. The Influence of Mother-Child Emotion Regulation Strategies on Children's Expression of Anger and Sadness

    ERIC Educational Resources Information Center

    Morris, Amanda Sheffield; Silk, Jennifer S.; Morris, Michael D. S.; Steinberg, Laurence; Aucoin, Katherine J.; Keyes, Angela W.

    2011-01-01

    In a sample of 153 children from preschool through second grade, relations between the use of emotion regulation strategy and children's expression of anger and sadness were coded during an observational task in which children were intentionally disappointed in the presence of the mother. Multilevel modeling was used to examine strategy use and…

  15. Maternal Socialization of Children's Anger, Sadness, and Physical Pain in Two Communities in Gujarat, India

    ERIC Educational Resources Information Center

    Raval, Vaishali Vidhatri; Martini, Tanya Susan

    2009-01-01

    Despite the recognition of cultural influences in child socialization, little is known about socialization of emotion in children from different cultures. This study examined (a) Gujarati Indian mothers' reports concerning their beliefs, affective and behavioral responses to their children's displays of anger, sadness, and physical pain, and (b)…

  16. The Experience of Anger and Sadness in Everyday Problems Impacts Age Differences in Emotion Regulation

    ERIC Educational Resources Information Center

    Blanchard-Fields, Fredda; Coats, Abby Heckman

    2008-01-01

    The authors examined regulation of the discrete emotions anger and sadness in adolescents through older adults in the context of describing everyday problem situations. The results support previous work; in comparison to younger age groups, older adults reported that they experienced less anger and reported that they used more passive and fewer…

  17. The Sad, the Mad and the Bad: Co-Existing Discourses of Girlhood

    ERIC Educational Resources Information Center

    Brown, Marion

    2011-01-01

    Three significant, prevailing and overlapping narratives of teenage girls have dominated North American popular consciousness since the early 1990s: the sad girl, victimized by male privilege and misogyny of adolescence and beyond; the mad grrrls who rejected this vulnerability through music and media; and the bad girls of much current popular…

  18. Influence of Intensity on Children's Sensitivity to Happy, Sad, and Fearful Facial Expressions

    ERIC Educational Resources Information Center

    Gao, Xiaoqing; Maurer, Daphne

    2009-01-01

    Most previous studies investigating children's ability to recognize facial expressions used only intense exemplars. Here we compared the sensitivity of 5-, 7-, and 10-year-olds with that of adults (n = 24 per age group) for less intense expressions of happiness, sadness, and fear. The developmental patterns differed across expressions. For…

  19. Misery is not miserly: sad and self-focused individuals spend more.

    PubMed

    Cryder, Cynthia E; Lerner, Jennifer S; Gross, James J; Dahl, Ronald E

    2008-06-01

    Misery is not miserly: Sadness increases the amount of money that decision makers give up to acquire a commodity. The present research investigated when and why the misery-is-not-miserly effect occurs. Drawing on William James's concept of the material self, we tested a model specifying relationships among sadness, self-focus, and the amount of money that decision makers spend. Consistent with our Jamesian hypothesis, results demonstrated that the misery-is-not-miserly effect occurs only when self-focus is high. That is, self-focus moderates the effect of sadness on spending. Moreover, mediational analyses revealed that, at sufficiently high levels, self-focus mediates (explains) the relationship between sadness and spending. Because the study used real commodities and real money, the results hold implications for everyday decisions, as well as implications for the development of theory. For example, economic theories of spending may benefit from incorporating psychological theories -- specifically, theories of emotion and the self -- into their models.

  20. Neural Substrates for Processing Task-Irrelevant Sad Images in Adolescents

    ERIC Educational Resources Information Center

    Wang, Lihong; Huettel, Scott; De Bellis, Michael D.

    2008-01-01

    Neural systems related to cognitive and emotional processing were examined in adolescents using event-related functional magnetic resonance imaging (fMRI). Ten healthy adolescents performed an emotional oddball task. Subjects detected infrequent circles (targets) within a continual stream of phase-scrambled images (standards). Sad and neutral…

  1. Anticipated Coping with Interpersonal Stressors: Links with the Emotional Reactions of Sadness, Anger, and Fear

    ERIC Educational Resources Information Center

    Zimmer-Gembeck, Melanie J.; Skinner, Ellen A.; Morris, Helen; Thomas, Rae

    2013-01-01

    The same stressor can evoke different emotions across individuals, and emotions can prompt certain coping responses. Responding to four videotaped interpersonal stressors, adolescents ("N" = 230, the average values of "X"[subscript age] = 10 years) reported their sadness, fear "and" anger, and 12 coping strategies.…

  2. The moderating role of personal relevance on differential priming of anxiety and sadness on perceived travel risk: a replication.

    PubMed

    Chiou, Wen-Bin; Chang, Ming-Hsu; Chen, Chien-Lung

    2009-04-01

    Raghunathan and Pham conducted a pioneer study in 1999 on the motivational influences of anxiety and sadness on decision making and indicated that anxiety would motivate individuals to be risk averse, whereas sadness would motivate individuals to be risk taking. A replication study was employed in the domain of perceived travel risk. Compared to participants in a neutral mood, anxious participants showed higher perceived travel risk than sad participants. Moreover, the differential effect of anxiety and sadness on perceived travel risk was only pronounced under the high personal relevance condition, in which participants made personal decisions and expected that they would be affected by the outcomes. In general, the results extend the notion proposed by Raghunathan and Pham suggesting that travelers' implicit goals primed by anxiety or sadness used for mood-repair purposes appear to be moderated by personal relevance. PMID:19610480

  3. Magnetospheric accretion on the T Tauri star BP Tauri

    NASA Astrophysics Data System (ADS)

    Donati, J.-F.; Jardine, M. M.; Gregory, S. G.; Petit, P.; Paletou, F.; Bouvier, J.; Dougados, C.; Ménard, F.; Collier Cameron, A.; Harries, T. J.; Hussain, G. A. J.; Unruh, Y.; Morin, J.; Marsden, S. C.; Manset, N.; Aurière, M.; Catala, C.; Alecian, E.

    2008-05-01

    From observations collected with the ESPaDOnS and NARVAL spectropolarimeters, we report the detection of Zeeman signatures on the classical T Tauri star (cTTS) BP Tau. Circular polarization signatures in photospheric lines and in narrow emission lines tracing magnetospheric accretion are monitored throughout most of the rotation cycle of BP Tau at two different epochs in 2006. We observe that rotational modulation dominates the temporal variations of both unpolarized and circularly polarized spectral proxies tracing the photosphere and the footpoints of accretion funnels. From the complete data sets at each epoch, we reconstruct the large-scale magnetic topology and the location of accretion spots at the surface of BP Tau using tomographic imaging. We find that the field of BP Tau involves a 1.2 kG dipole and 1.6 kG octupole, both slightly tilted with respect to the rotation axis. Accretion spots coincide with the two main magnetic poles at high latitudes and overlap with dark photospheric spots; they cover about 2 per cent of the stellar surface. The strong mainly axisymmetric poloidal field of BP Tau is very reminiscent of magnetic topologies of fully convective dwarfs. It suggests that magnetic fields of fully convective cTTSs such as BP Tau are likely not fossil remants, but rather result from vigorous dynamo action operating within the bulk of their convective zones. Preliminary modelling suggests that the magnetosphere of BP Tau extends to distances of at least 4R* to ensure that accretion spots are located at high latitudes, and is not blown open close to the surface by a putative stellar wind. It apparently succeeds in coupling to the accretion disc as far out as the corotation radius, and could possibly explain the slow rotation of BP Tau. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) and at the Télescope Bernard Lyot (TBL). CFHT is operated by the National Research Council of Canada, the Institut National des Sciences de l

  4. The artificial disc: theory, design and materials.

    PubMed

    Bao, Q B; McCullen, G M; Higham, P A; Dumbleton, J H; Yuan, H A

    1996-06-01

    Low back pain is one of the most common medical conditions in the Western world. Disc degeneration, an inevitable process of aging, of variable rate and degree, is one of the major causes of low back pain. Currently, there are two major surgical interventions for treating conditions related to the degenerative disc: discectomy and fusion. Although discectomy and fusion produce a relatively good short-term clinical result in relieving pain, both these surgical treatments alter the biomechanics of the spine, possibly leading to further degeneration of the surrounding tissues and the discs at adjacent levels. Over the past 35 years, a tremendous effort has been made to develop an artificial disc to replace the degenerated disc. The goal is the restoration of the natural biomechanics of the segment after disc excision, thus relieving pain and preventing further degeneration at adjacent segments. However, the artificial disc faces a complex biomechanical environment which makes replication of the biomechanics difficult and long-term survival challenging to designs and materials. The purpose of this article is to examine the factors of importance in designing a disc replacement. Topics covered include the structure and function of the natural disc, the changes that occur with disc degeneration and existing methods of treatment for the degenerative spine. The progress in achieving a functional, long-lasting disc replacement is outlined.

  5. Terrestrial accretion under oxidizing conditions.

    PubMed

    Siebert, Julien; Badro, James; Antonangeli, Daniele; Ryerson, Frederick J

    2013-03-01

    The abundance of siderophile elements in the mantle preserves the signature of core formation. On the basis of partitioning experiments at high pressure (35 to 74 gigapascals) and high temperature (3100 to 4400 kelvin), we demonstrate that depletions of slightly siderophile elements (vanadium and chromium), as well as moderately siderophile elements (nickel and cobalt), can be produced by core formation under more oxidizing conditions than previously proposed. Enhanced solubility of oxygen in the metal perturbs the metal-silicate partitioning of vanadium and chromium, precluding extrapolation of previous results. We propose that Earth accreted from materials as oxidized as ordinary or carbonaceous chondrites. Transfer of oxygen from the mantle to the core provides a mechanism to reduce the initial magma ocean redox state to that of the present-day mantle, reconciling the observed mantle vanadium and chromium concentrations with geophysical constraints on light elements in the core. PMID:23306436

  6. Why Do T Tauri Disks Accrete?

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee; D'Alessio, Paola; Calvet, Nuria; Muzerolle, James

    2006-01-01

    Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks scales roughly with the square of the central stellar mass. No dependence of accretion rate on stellar mass is predicted by the simplest version of the Gammie layered disk model, in which nonthermal ionization of upper disk layers allows accretion to occur via the magnetorotational instability. We show that a minor modification of Gaminie's model to include heating by irradiation from the central star yields a modest dependence of accretion on the mass of the central star. A purely viscous disk model could provide a strong dependence of accretion rate on stellar mass if the initial disk radius (before much viscous evolution has occurred) has a strong dependence on stellar mass. However, it is far from clear that at least the most massive pre-main-sequence disks can be totally magnetically activated by X-rays or cosmic rays. We suggest that a combination of effects are responsible for the observed dependence, with the lowest mass stars having the lowest mass disks, which can be thoroughly magnetically active, while the higher mass stars have higher mass disks that have layered accret,ion and relatively inactive or "dead" central zones at some radii. In such dead zones, we suggest that gravitational instabilities may play a role in allowing accretion to proceed. In this connection, we emphasize the uncertainty in disk masses derived from dust emission and argue that T Tauri disk masses have been systematically underestimated by conventional analyses. Furtlier study of accretion rates, especially in the lowest mass stars, would help to clarify the mechanisms of accretion in T Tauri stars.

  7. A Functional MRI Study of Happy and Sad Emotions in Music with and without Lyrics.

    PubMed

    Brattico, Elvira; Alluri, Vinoo; Bogert, Brigitte; Jacobsen, Thomas; Vartiainen, Nuutti; Nieminen, Sirke; Tervaniemi, Mari

    2011-01-01

    Musical emotions, such as happiness and sadness, have been investigated using instrumental music devoid of linguistic content. However, pop and rock, the most common musical genres, utilize lyrics for conveying emotions. Using participants' self-selected musical excerpts, we studied their behavior and brain responses to elucidate how lyrics interact with musical emotion processing, as reflected by emotion recognition and activation of limbic areas involved in affective experience. We extracted samples from subjects' selections of sad and happy pieces and sorted them according to the presence of lyrics. Acoustic feature analysis showed that music with lyrics differed from music without lyrics in spectral centroid, a feature related to perceptual brightness, whereas sad music with lyrics did not diverge from happy music without lyrics, indicating the role of other factors in emotion classification. Behavioral ratings revealed that happy music without lyrics induced stronger positive emotions than happy music with lyrics. We also acquired functional magnetic resonance imaging data while subjects performed affective tasks regarding the music. First, using ecological and acoustically variable stimuli, we broadened previous findings about the brain processing of musical emotions and of songs versus instrumental music. Additionally, contrasts between sad music with versus without lyrics recruited the parahippocampal gyrus, the amygdala, the claustrum, the putamen, the precentral gyrus, the medial and inferior frontal gyri (including Broca's area), and the auditory cortex, while the reverse contrast produced no activations. Happy music without lyrics activated structures of the limbic system and the right pars opercularis of the inferior frontal gyrus, whereas auditory regions alone responded to happy music with lyrics. These findings point to the role of acoustic cues for the experience of happiness in music and to the importance of lyrics for sad musical emotions.

  8. A Functional MRI Study of Happy and Sad Emotions in Music with and without Lyrics

    PubMed Central

    Brattico, Elvira; Alluri, Vinoo; Bogert, Brigitte; Jacobsen, Thomas; Vartiainen, Nuutti; Nieminen, Sirke; Tervaniemi, Mari

    2011-01-01

    Musical emotions, such as happiness and sadness, have been investigated using instrumental music devoid of linguistic content. However, pop and rock, the most common musical genres, utilize lyrics for conveying emotions. Using participants’ self-selected musical excerpts, we studied their behavior and brain responses to elucidate how lyrics interact with musical emotion processing, as reflected by emotion recognition and activation of limbic areas involved in affective experience. We extracted samples from subjects’ selections of sad and happy pieces and sorted them according to the presence of lyrics. Acoustic feature analysis showed that music with lyrics differed from music without lyrics in spectral centroid, a feature related to perceptual brightness, whereas sad music with lyrics did not diverge from happy music without lyrics, indicating the role of other factors in emotion classification. Behavioral ratings revealed that happy music without lyrics induced stronger positive emotions than happy music with lyrics. We also acquired functional magnetic resonance imaging data while subjects performed affective tasks regarding the music. First, using ecological and acoustically variable stimuli, we broadened previous findings about the brain processing of musical emotions and of songs versus instrumental music. Additionally, contrasts between sad music with versus without lyrics recruited the parahippocampal gyrus, the amygdala, the claustrum, the putamen, the precentral gyrus, the medial and inferior frontal gyri (including Broca’s area), and the auditory cortex, while the reverse contrast produced no activations. Happy music without lyrics activated structures of the limbic system and the right pars opercularis of the inferior frontal gyrus, whereas auditory regions alone responded to happy music with lyrics. These findings point to the role of acoustic cues for the experience of happiness in music and to the importance of lyrics for sad musical emotions

  9. Model dependence of the multi-transonic behaviour, stability properties and the corresponding acoustic geometry for accretion onto rotating black holes

    NASA Astrophysics Data System (ADS)

    Saha, Sonali; Sen, Sharmistha; Nag, Sankhasubhra; Raychowdhury, Suparna; Das, Tapas K.

    2016-02-01

    Stationary, multi-transonic, integral solutions of hydrodynamic axisymmetric accretion onto a rotating black hole have been compared for different geometrical configurations of the associated accretion disc structures described using the polytropic as well as the isothermal equations of state. Such analysis is performed for accretion under the influence of generalised post Newtonian pseudo Kerr black hole potential. The variations of the stationary shock characteristics with black hole spin have been studied in details for all the disc models and are compared for the flow characterised by the two aforementioned equations of state. Using a novel linear perturbation technique it has been demonstrated that the aforementioned stationary solutions are stable, at least upto an astrophysically relevant time scale. It has been demonstrated that the emergence of the horizon related gravity like phenomena (the analogue gravity effects) is a natural consequence of such stability analysis, and the corresponding acoustic geometry embedded within the transonic accretion can be constructed for the propagation of the linear acoustic perturbation of the mass accretion rate. The analytical expression for the associated sonic surface gravity κ has been obtained self consistently. The variations of κ with the black hole spin parameter for all different geometric configurations of matter and for various thermodynamic equations of state have been demonstrated.

  10. Dust settling in magnetorotationally driven turbulent discs - I. Numerical methods and evidence for a vigorous streaming instability

    NASA Astrophysics Data System (ADS)

    Balsara, Dinshaw S.; Tilley, David A.; Rettig, Terrence; Brittain, Sean D.

    2009-07-01

    In this paper, we have used the RIEMANN code for computational astrophysics to study the interaction of a realistic distribution of dust grains with gas at specific radial locations in a vertically stratified protostellar accretion disc. The disc was modelled to have the density and temperature of a minimum mass solar nebula, and shearing box simulations at radii of 0.3 and 10 au are reported here. The disc was driven to a fully developed turbulence via the magnetorotational instability (MRI). The simulations span three gas scaleheights about the disc's midplane. We find that the inclusion of standard dust-to-gas ratios does not have any significant effect on the MRI even when the dust sediments to the midplane of the accretion disc. The density distribution of the dust of all sizes reached a Gaussian profile within two scaleheights of the disc's midplane. The vertical scaleheights of these Gaussian profiles are shown to be proportional to the reciprocal of the square root of the dust radius when large spherical dust grains are considered. This result is consistent with theoretical expectation. The largest two families of dust in one of our simulations show a strong tendency to settle to the midplane of the accretion disc. The large dust tends to organize itself into elongated clumps of high density. The dynamics of these clumps is shown to be consistent with a streaming instability. The streaming instability is seen to be very vigorous and persistent once it forms. Each stream of high-density dust displays a reduced rms velocity dispersion. The velocity directions within the streams are also aligned relative to the mean shear, providing further evidence that we are witnessing a streaming instability. The densest clumpings of large dust are shown to form where the streams intersect. We have also shown that the mean free path and collision time for dust that participates in the streaming instability are reduced by almost two orders of magnitude relative to the

  11. Echo Tomography of Hercules X-1: Mapping the Accretion Disc with RXTE and HST

    NASA Technical Reports Server (NTRS)

    Vrtilek, S.

    2000-01-01

    A paper based on the RXTE results contents the following and are ready for submission to ApJ: "Possible Detection of Companion Star Reflection from Hercules X-1 with RXTE". A paper combining July 1998 and July 1999 observations (including the RXTE results for both years) is nearly ready for submission to ApJ: The July 1998 and July 1999 Multiwavelength Campaigns on Hercules X-I/HZ Herculis. The July 1999 observations took place during an anomalous X-ray low state and the RXTE and EUVE data are consistent with X_ray reflected from the surface of the companion star.

  12. [Innervation of the intervertebral disc].

    PubMed

    García-Cosamalón, José; Fernández-Fernández, Javier; González-Martínez, Emilio; Ibáñez-Plágaro, Javier; Robla Costales, Javier; Martínez-Madrigal, Milton; López Muñíz, Alfonso; del Valle, Miguel Enrique; Vega, José Antonio

    2013-01-01

    Until very recently, intervertebral disc innervation was a subject of considerable debate. Nowadays, the introduction of inmunohistochemical techniques associated to specific antibodies and studies with retrograde tracers in nerves have allowed greater understanding of disc innervation in physiological and pathological conditions and also endings characteristics and their patterns of distribution in both situations. The existing controversies regarding structural basis of discogenic pain, have raised the interest of knowing the influence of innervation in back pain from discal origin and its characteristics. Today, we know that pathologic neoinnervation accompanying radial fissures is an important factor in the genesis of discogenic pain; within a complex mechanism in which other neurobiomechemical, inflammatory and biomechanical factors are involved. PMID:23582224

  13. Probing the disc wind-jet connection in black hole transients

    NASA Astrophysics Data System (ADS)

    Diaz Trigo, Maria

    2010-10-01

    We propose 4 observations of one high inclination black hole low mass X-ray binary (LMXB) at different stages of its outburst. We will investigate the presence of X-ray narrow absorption/emission features in the XMM spectra, which are a signature of a disc wind, and their relation to the accreting regime. Such features, identified with ions like FeXXV and FeXXVI, have been observed in a number of LMXBs and give us information about the mass outflow rate and the launching mechanism of the wind. With simultaneous radio observations we will probe the jet power as a function of the wind properties and how the radio flux density correlates with the X-ray flux at different accretion regimes. We will also investigate the broadening mechanism of the FeK emission line detected up to now in several LMXBs.

  14. Probing the disc wind-jet connection in black hole transients II

    NASA Astrophysics Data System (ADS)

    Diaz Trigo, Maria

    2013-10-01

    We propose six observations of one high inclination black hole low mass X-ray binary (LMXB) at different stages of its outburst. We will investigate the presence of X-ray narrow absorption/emission features in the XMM spectra, which are a signature of a disc wind, and their relation to the accreting regime. Such features, identified with ions like FeXXV and FeXXVI, have been observed in a number of LMXBs and give us information about the mass outflow rate and the launching mechanism of the wind. With simultaneous radio observations we will probe the jet power as a function of the wind properties and how the radio flux density correlates with the X-ray flux at different accretion regimes. We will also investigate the broadening mechanism of the FeK emission line detected up to now in several LMXBs.

  15. 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

  16. Spectrum of a jet-emitting disc: application to the microquasar XTE J1118+480

    NASA Astrophysics Data System (ADS)

    Zhang, Jian-Fu; Xie, Fu-Guo

    2013-10-01

    Under the framework of the magnetized accretion ejection structures, we analyse the energy balance properties, and study the spectral energy distributions (SEDs) of the jet-emitting disc (JED) model for black hole X-ray transients. Various radiative processes are considered, i.e. synchrotron, bremsstrahlung, and their Comptonizations, and external Comptonization of radiation from the outer thin disc. With these cooling terms taken into account, we solve the thermal equilibrium equation self-consistently and find three solutions, of which the cold and the hot solutions are stable. Subsequently, we investigate the theoretical SEDs for these two stable solutions. We find the hot JED model can naturally explain the spectra of the Galactic microquasars in their hard states. As an example, we apply this model to the case of XTE J1118+480.

  17. The Aerodynamics of a Flying Sports Disc

    NASA Astrophysics Data System (ADS)

    Potts, Jonathan R.; Crowther, William J.

    2001-11-01

    The flying sports disc is a spin-stabilised axi-symmetric wing of quite remarkable design. A typical disc has an approximate elliptical cross-section and hollowed out under-side cavity, such as the Frisbee(TM) disc. An experimental study of flying disc aerodynamics, including both spinning and non-spinning tests, has been carried out in the wind tunnel. Load measurements, pressure data and flow visualisation techniques have enabled an explanation of the flow physics and provided data for free-flight simulations. A computer simulation that predicts free-flight trajectories from a given set of initial conditions was used to investigate the dynamics of a flying disc. This includes a six-degree of freedom mathematical model of disc flight mechanics, with aerodynamic coefficients derived from experimental data. A flying sports disc generates lift through forward velocity just like a conventional wing. The lift contributed by spin is insignificant and does not provide nearly enough down force to support hover. Without spin, the disc tumbles ground-ward under the influence of an unstable aerodynamic pitching moment. From a backhand throw however, spin is naturally given to the disc. The unchanged pitching moment now results in roll, due to gyroscopic precession, stabilising the disc in free-flight.

  18. 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

  19. Outflows from Accretion Disks around Compact Objects

    NASA Astrophysics Data System (ADS)

    Jiao, Cheng-Liang; Wu, Xue-Bing

    2013-02-01

    We solve the set of hydrodynamic equations for accretion disks in the spherical coordinates (rθφ) to obtain the explicit structure along the θ direction. The results display thinner, quasi-Keplerian disks for Shakura-Sunyaev Disks (SSDs) and thicker, sub-Keplerian disks for Advection Dominated Accretion Flows (ADAFs) and slim disks, which are consistent with previous popular analytical models, while an inflow region and an outflow region always exist, which supports the results of some recent numerical simulation works. Our results indicate that the outflows should be common in various accretion disks and stronger in slim disks and ADAFs.

  20. Extremes of the jet-accretion power relation of blazars, as explored by NuSTAR

    NASA Astrophysics Data System (ADS)

    Sbarrato, T.; Ghisellini, G.; Tagliaferri, G.; Perri, M.; Madejski, G. M.; Stern, D.; Boggs, S. E.; Christensen, F. E.; Craig, W. W.; Hailey, C. J.; Harrison, F. A.; Zhang, W. W.

    2016-10-01

    Hard X-ray observations are crucial to study the non-thermal jet emission from high-redshift, powerful blazars. We observed two bright z > 2 flat-spectrum radio quasars (FSRQs) in hard X-rays to explore the details of their relativistic jets and their possible variability. S5 0014+81 (at z = 3.366) and B0222+185 (at z = 2.690) have been observed twice by the Nuclear Spectroscopic Telescope Array (NuSTAR) simultaneously with Swift/X-ray Telescope, showing different variability behaviours. We found that NuSTAR is instrumental to explore the variability of powerful high-redshift blazars, even when no γ-ray emission is detected. The two sources have proven to have respectively the most luminous accretion disc and the most powerful jet among known blazars. Thanks to these properties, they are located at the extreme end of the jet-accretion disc relation previously found for γ-ray detected blazars, to which they are consistent.

  1. The effects of a magnetic field on planetary migration in laminar and turbulent discs

    NASA Astrophysics Data System (ADS)

    Comins, Megan L.; Romanova, Marina M.; Koldoba, Alexander V.; Ustyugova, Galina V.; Blinova, Alisa A.; Lovelace, Richard V. E.

    2016-07-01

    We investigate the migration of low-mass planets (1, 5 and 20 M⊕) in accretion discs threaded with a magnetic field using 2D magnetohydrodynamic code in polar coordinates. We observed that, in the case of a strong azimuthal magnetic field where the plasma parameter is β ˜ 2-4, density waves at the magnetic resonances exert a positive torque on the planet and may slow down or reverse its migration. However, when the magnetic field is weaker (i.e. the plasma parameter β is relatively large), then non-axisymmetric density waves excited by the planet lead to growth of the radial component of the field and, subsequently, to development of the magnetorotational instability, such that the disc becomes turbulent. Migration in a turbulent disc is stochastic, and the migration direction may change as such. To understand migration in a turbulent disc, both the interaction between a planet and individual turbulent cells, as well as the interaction between a planet and ordered density waves, have been investigated.

  2. Observations vs theory: from metallicity correlations of exoplanets and debris discs to HL Tau

    NASA Astrophysics Data System (ADS)

    Nayakshin, Sergei V.

    2015-12-01

    Boley et al (2010) and Nayakshin (2010) proposed Tidal Downsizing (TD), a new hypothesis for forming all types of planets. Gas fragments born by gravitational disc instability at ~ 100 AU migrate inwards rapidly, with some becoming hot Jupiters. Grain sedimentation inside the fragments makes rocky cores. These cores are future Earths and Super Earths, leaved behind when most of the migrating fragments are tidally disrupted.TD can now be tested against data in detail thanks to a numerical population synthesis model (Nayakshin and Fletcher 2015). TD scenario is fundamentally different from Core Accretion (CA), with sub-Saturn planets and debris discs born in gas fragment disruptions, and not vice versa. I therefore find robust observational differences between CA and TD despite uncertainties inherent in any population synthesis. Here I use metallicity correlations of all sorts to test the model. In TD, the only population that correlates with metallicity (Z) of the host strongly is that of moderately massive gas giants interior to a few AU from the host. Super-Earths and debris discs correlate in mass but not in numbers with Z; very massive gas giants, brown dwarfs and directly imaged gas giants are neutral to Z. Fragment self-destruction by core feedback explains simultaneously the core mass function roll-over at ~20 Earth masses, the rapid formation of suspected planets in HL Tau, and the paucity of directly imaged gas giants. Debris discs and gas giants do not correlate in TD, as observed.I argue that TD does a better job in accounting for many of the observed properties of exoplanets and planetary debris than CA. I finish with observational predictions that can distinguish TD from Core Accretion in the near future.

  3. 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.

  4. Palaeoclimate, Sedimentation and Continental Accretion

    NASA Astrophysics Data System (ADS)

    Ziegler, A. M.; Barrett, S. F.; Scotese, C. R.

    1981-05-01

    Climate has a pervasive effect on sedimentation today, and the same climatic patterns are reflected in the distribution of lithofacies through the Palaeozoic, as the continents migrate beneath the climatic zones. The low-latitude hot wet zone is represented by thick clastics, coals and carbonates and is best developed along east coasts where prevailing winds bring moisture and heated surface waters toward the continent. The desert zones occur on the west sides of continents centred at 20 degrees north and south, and these dry belts are represented in the geological record by evaporites. Tillites, thick clastics and coals occur in the temperate rainy belts, especially on the windward, west sides of continents above 40 degrees latitude. Continental accretion occurs where subduction zones coincide with rainy zones, such that the products of erosion are transported to the trench, and thus thrust back, extending the margin of the continent. The opposite process of `tectonic erosion', wherein the descending oceanic slab continually `rasps' away the margin of the continental crust, may occur in areas where rainfall and surface run-off is insufficient to provide trench sediments. This process has been operating adjacent to the Atacama Desert in South America during the past 200 Ma. To judge by the eastward migration of the calc-alkaline intrusive foci, about 250 km of the margin of South America have been transported down the subduction zone during this period.

  5. 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.

  6. Heat transfer on accreting ice surfaces

    NASA Technical Reports Server (NTRS)

    Yamaguchi, Keiko; Hansman, R. John, Jr.

    1993-01-01

    Based on previous observations of glaze ice accretion on aircraft surfaces, a multizone model with distinct zones of different surface roughness is demonstrated. The use of surface roughness in the LEWICE ice accretion prediction code is examined. It was found that roughness is used in two ways: (1) to determine the laminar to turbulent boundary-layer transition location; and (2) to calculate the convective turbulent heat-transfer coefficient. A two-zone version of the multizone model is implemented in the LEWICE code, and compared with experimental convective heat-transfer coefficient and ice accretion results. The analysis of the boundary-layer transition, surface roughness, and viscous flowfield effects significantly increased the accuracy in predicting heat-transfer coefficients. The multizone model was found to significantly improve the ice accretion prediction for the cases compared.

  7. Accretion of Ghost Condensate by Black Holes

    SciTech Connect

    Frolov, A

    2004-06-02

    The intent of this letter is to point out that the accretion of a ghost condensate by black holes could be extremely efficient. We analyze steady-state spherically symmetric flows of the ghost fluid in the gravitational field of a Schwarzschild black hole and calculate the accretion rate. Unlike minimally coupled scalar field or quintessence, the accretion rate is set not by the cosmological energy density of the field, but by the energy scale of the ghost condensate theory. If hydrodynamical flow is established, it could be as high as tenth of a solar mass per second for 10MeV-scale ghost condensate accreting onto a stellar-sized black hole, which puts serious constraints on the parameters of the ghost condensate model.

  8. Review of gravitomagnetic acceleration from accretion disks

    NASA Astrophysics Data System (ADS)

    Poirier, J.; Mathews, G. J.

    2015-11-01

    We review the development of the equations of gravitoelectromagnetism and summarize how the motion of the neutral masses in an accretion disk orbiting a black hole creates a general-relativistic magnetic-like (gravitomagnetic) field that vertically accelerates neutral particles near the accretion disk upward and then inward toward the axis of the accretion disk. Even though this gravitomagnetic field is not the only mechanism to produce collimated jets, it is a novel means to identify one general relativistic effect from a much more complicated problem. In addition, as the accelerated material above or below the accretion disk nears the axis with a nearly vertical direction, a frame-dragging effect twists the trajectories around the axis thus contributing to the collimation of the jet.

  9. Gravitomagnetic acceleration from black hole accretion disks

    NASA Astrophysics Data System (ADS)

    Poirier, J.; Mathews, G. J.

    2016-05-01

    We demonstrate how the motion of the neutral masses in an accretion disk orbiting a black hole creates a general-relativistic magnetic-like (gravitomagnetic) field that vertically accelerates neutral particles near an accretion disk upward and then inward toward the axis of the accretion disk. Even though this gravitomagnetic field is not the only mechanism contributing to the production of jets, it presents a novel means to identify one general relativistic effect from a much more complicated problem. In addition, as the accelerated material above or below the accretion disk nears the axis with a nearly vertical direction, a frame-dragging effect twists the trajectories around the axis thus contributing to the collimation of the jet.

  10. Planetary science: Iron fog of accretion

    SciTech Connect

    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.

  11. Disc wear and entrapment in a Starr-Edwards mitral caged-disc valve.

    PubMed

    Aoyagi, Shigeaki; Fukunaga, Shuji; Arinaga, Koichi

    2011-07-01

    A case of wear and entrapment of a polyethylene disc observed in a Starr-Edwards (SE) mitral caged-disc valve at 37 years after implantation is reported. A 66-year-old woman who had undergone mitral valve replacement with a SE disc valve 37 years previously was admitted to the authors' hospital. Cinefluoroscopy showed the polyethylene disc of the SE valve to have impinged against a calcified mass on the left ventricular posterior wall, causing a tipping motion of the disc during opening. The valve was successfully replaced at surgery. A macroscopic examination of the excised valve revealed wear of the polyethylene disc at sites where the disc abutted the cage struts, and where it impinged on the calcified mass. The long-term durability of the SE caged-disc valves has been favorable; however, when implanted for over 20 years, they should be carefully followed up.

  12. Sad as a Matter of Choice? Emotion-Regulation Goals in Depression.

    PubMed

    Millgram, Yael; Joormann, Jutta; Huppert, Jonathan D; Tamir, Maya

    2015-08-01

    Research on deficits in emotion regulation has devoted considerable attention to emotion-regulation strategies. We propose that deficits in emotion regulation may also be related to emotion-regulation goals. We tested this possibility by assessing the direction in which depressed people chose to regulate their emotions (i.e., toward happiness, toward sadness). In three studies, clinically depressed participants were more likely than nondepressed participants to use emotion-regulation strategies in a direction that was likely to maintain or increase their level of sadness. This pattern was found when using the regulation strategies of situation selection (Studies 1 and 2) and cognitive reappraisal (Study 3). The findings demonstrate that maladaptive emotion regulation may be linked not only to the means people use to regulate their emotions, but also to the ends toward which those means are directed. PMID:26092058

  13. Cardiovascular, electrodermal, and respiratory response patterns to fear- and sadness-inducing films.

    PubMed

    Kreibig, Sylvia D; Wilhelm, Frank H; Roth, Walton T; Gross, James J

    2007-09-01

    Responses to fear- and sadness-inducing films were assessed using a broad range of cardiovascular (heart rate, T-wave amplitude, low- and high-frequency heart rate variability, stroke volume, preejection period, left-ventricular ejection time, Heather index, blood pressure, pulse amplitude and transit time, and finger temperature), electrodermal (level, response rate, and response amplitude), and respiratory (rate, tidal volume and its variability, inspiratory flow rate, duty cycle, and end-tidal pCO(2)) measures. Subjective emotional experience and facial behavior (Corrugator Supercilii and Zygomaticus Major EMG) served as control measures. Results indicated robust differential physiological response patterns for fear, sadness, and neutral (mean classification accuracy 85%). Findings are discussed in terms of the fight-flight and conservation-withdrawal responses and possible limitations of a valence-arousal categorization of emotion in affective space.

  14. The Unique and Shared Genetic and Environmental Contributions to Fear, Anger, and Sadness in Childhood

    PubMed Central

    Clifford, Sierra; Lemery-Chalfant, Kathryn; Goldsmith, H. Hill

    2015-01-01

    This study examined the extent to which subordinate dimensions of negative emotionality were genetically and environmentally distinct in a sample of 1316 twins (51% female, 85.8% Caucasian, primarily middle class, mean age = 7.87 years, SD = .93), recruited from Wisconsin hospital birth records between 1989 and 2004. Cholesky, independent pathway, and common pathway models were fitted for mother-report, father-report, and in-home observation of temperament. Although findings support the use of negative emotionality, there were heritable aspects of anger and fear not explained by a common genetic factor, and shared environmental influences common to anger and sadness but not fear. Observed fear was independent from observed anger and sadness. Distinctions support specificity in measurement when considering implications for child development. PMID:26182850

  15. Caregiver Protective Behavior, Toddler Fear and Sadness, and Toddler Cortisol Reactivity in Novel Contexts

    PubMed Central

    Hutt, Rachel L.; Buss, Kristin A.; Kiel, Elizabeth J.

    2012-01-01

    Previous research has shown that caregiver protective behavior may exacerbate toddler distress in specific contexts. The current study sought to extend this work to examine associations between these variables and toddler cortisol reactivity. Ninety-three 24-month-old toddlers were observed across six novel contexts designed to elicit distress. Toddlers were asked to give saliva samples at the beginning and end of the laboratory procedure. Toddler sadness, toddler fear, and caregiver protective behavior were coded. Results indicate that caregiver protective behavior accounted for the association between toddler sadness and cortisol reactivity where higher levels of protective behavior were associated with higher cortisol reactivity. The current study showed that caregiver protective behavior, which functions to prevent a child from interacting with a novel stimulus, is an important mechanism to consider when understanding toddler stress responses during novel contexts. PMID:24659922

  16. Sadness shifts to anxiety with time and distance from national tragedy in Newtown CT

    PubMed Central

    Doré, Bruce; Ort, Leonard; Braverman, Ofir; Ochsner, Kevin

    2015-01-01

    How do increasing temporal and spatial distance impact the emotions we feel and express in response to tragic events? Standard views suggest decreases in emotional intensity but are silent on changes in emotional quality. Using a large Twitter dataset, we identified temporal and spatial patterns in emotional and cognitive word use on the topic of the Sandy Hook Elementary School shooting. Although sadness words decreased with time and distance, anxiety words showed the opposite pattern, associated with concurrent increases in language reflecting causal thinking. In a follow-up experiment, we found that thinking about abstract causes (versus concrete details) of this event similarly evoked decreased sadness but increased anxiety, which was associated with perceptions that a similar event may occur in the future. These data challenge current theories of emotional reactivity and identify time, space, and abstract causal thinking as factors that elicit categorical shifts in emotional responses to tragedy. PMID:25767209

  17. 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.

  18. The quiescent phase of galactic disc growth

    NASA Astrophysics Data System (ADS)

    Aumer, Michael; Binney, James; Schönrich, Ralph

    2016-07-01

    We perform a series of controlled N-body simulations of growing disc galaxies within non-growing, live dark matter haloes of varying mass and concentration. Our initial conditions include either a low-mass disc or a compact bulge. New stellar particles are continuously added on near-circular orbits to the existing disc, so spiral structure is continuously excited. To study the effect of combined spiral and giant molecular cloud (GMC) heating on the discs, we introduce massive, short-lived particles that sample a GMC mass function. An isothermal gas component is introduced for a subset of the models. We perform a resolution study and vary parameters governing the GMC population, the histories of star formation and radial scale growth. Models with GMCs and standard values for the disc mass and halo density provide the right level of self-gravity to explain the age-velocity dispersion relation of the solar neighbourhood (Snhd). GMC heating generates remarkably exponential vertical profiles with scaleheights that are radially constant and agree with observations of galactic thin discs. GMCs are also capable of significantly delaying bar formation. The amount of spiral-induced radial migration agrees with what is required for the metallicity distribution of the Snhd. However, in our standard models, the outward-migrating populations are not hot enough vertically to create thick discs. Thick discs can form in models with high baryon fractions, but the corresponding bars are too long, the young stellar populations too hot and the discs flare considerably.

  19. Stability of MRI Turbulent Accretion Disks

    NASA Astrophysics Data System (ADS)

    Takahashi, H. R.; Masada, Y.

    2010-12-01

    We study the stability of geometrically thin accretion disks with non-standard α parameter, which characterizes the efficiency of the angular momentum transport. Following recent results of numerical simulations of the Magnetorotational instability (MRI) driven turbulence, we assume that α increases with the magnetic Prandtl number. By adopting Spitzer's microscopic diffusivities, we obtain local structures of geometrically thin accretion disks consistently including effects of MRI-driven turbulence. Since the magnetic Prandtl number increases with the temperature, the efficiency of the angular momentum transport and thus viscous heating rate are smaller for a larger radius when δ > 0. We find that such disks can be unstable to gravitational, thermal, and secular instabilities. It is most remarkable feature that the thermal and secular instabilities can grow in the middle part of accretion disks even when the radiation pressure is negligible, while the standard Shakura