WorldWideScience

Sample records for accretion discs due

  1. Relativistic reflection from accretion disc ionised due to illumination from on-axis compact corona

    Science.gov (United States)

    Dovciak, M.; Guainazzi, M.; Svoboda, J.

    2014-07-01

    We re-visit the relativistic (light bending) reflection scenario of AGN spectra in the lamp-post geometry. We compute the ionisation of the disc consistently with the amount of illumination from the on-axis compact corona. In this model the ionisation pattern of the disc is dependent on the distance from the centre according to astrophysically-motivated assumptions. We investigate the complementarity of different model parameters like: a) the intrinsic primary flux and the height of the corona, both affecting the normalization of the observed primary power-law; b) the height of the corona and the black hole spin, both affecting the amount of radiation emitted from the innermost regions of the disc; and c) the intrinsic primary flux, the height of the corona and the density of the disc, the three parameters that affect the ionisation state of the disc. We examine how these complementarities manifest themselves when fitting X-ray broadband spectra of the Seyfert 1 Galaxy MCG-6-30-15.

  2. FRB as products of accretion disc funnels

    Science.gov (United States)

    Katz, J. I.

    2017-10-01

    The repeating FRB 121102, the only fast radio burst (FRB) with an accurately determined position, is associated with a variable persistent radio source. I suggest that an FRB originates in the accretion disc funnels of black holes. Narrowly collimated radiation is emitted along the wandering instantaneous angular momentum axis of accreted matter. This emission is observed as a fast radio burst when it sweeps across the direction to the observer. In this model, in contrast to neutron star (pulsar, RRAT or SGR) models, repeating FRBs do not have underlying periodicity and are co-located with persistent radio sources resulting from their off-axis emission. The model is analogous, on smaller spatial, lower mass and accretion rate and shorter temporal scales, to an active galactic nucleus (AGN), with FRB corresponding to blazars in which the jets point towards us. The small inferred black hole masses imply that FRBs are not associated with galactic nuclei.

  3. On the illumination of neutron star accretion discs

    Science.gov (United States)

    Wilkins, D. R.

    2018-03-01

    The illumination of the accretion disc in a neutron star X-ray binary by X-rays emitted from (or close to) the neutron star surface is explored through general relativistic ray tracing simulations. The applicability of the canonical suite of relativistically broadened emission line models (developed for black holes) to discs around neutron stars is evaluated. These models were found to describe well emission lines from neutron star accretion discs unless the neutron star radius is larger than the innermost stable orbit of the accretion disc at 6 rg or the disc is viewed at high inclination, above 60° where shadowing of the back side of the disc becomes important. Theoretical emissivity profiles were computed for accretion discs illuminated by hotspots on the neutron star surfaces, bands of emission and emission by the entirety of the hot, spherical star surface and in all cases, the emissivity profile of the accretion disc was found to be well represented by a single power law falling off slightly steeper than r-3. Steepening of the emissivity index was found where the emission is close to the disc plane and the disc can appear truncated when illuminated by a hotspot at high latitude. The emissivity profile of the accretion disc in Serpens X-1 was measured and found to be consistent with a single unbroken power law with index q=3.5_{-0.4}^{+0.3}, suggestive of illumination by the boundary layer between the disc and neutron star surface.

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

    Science.gov (United States)

    Hennebelle, Patrick; Lesur, Geoffroy; Fromang, Sébastien

    2017-03-01

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

  5. Spectral properties of the accretion discs around rotating black holes

    Indian Academy of Sciences (India)

    Samir Mandal

    2018-02-10

    Feb 10, 2018 ... Abstract. We study the radiation properties of an accretion disc around a rotating black hole. We solve the hydrodynamic equations and calculate the transonic solutions of accretion disc in the presence of shocks. Then we use these solutions to generate the radiation spectrum in the presence of radiative ...

  6. Generation of inclined protoplanetary discs and misaligned planets through mass accretion - I. Coplanar secondary discs

    Science.gov (United States)

    Xiang-Gruess, M.; Kroupa, P.

    2017-10-01

    We study the three-dimensional (3D) evolution of a viscous protoplanetary disc that accretes gas material from a second protoplanetary disc during a close encounter in an embedded star cluster. The aim is to investigate the capability of the mass accretion scenario to generate strongly inclined gaseous discs that could later form misaligned planets. We use smoothed particle hydrodynamics to study mass transfer and disc inclination for passing stars and circumstellar discs with different masses. We explore different orbital configurations to find the parameter space that allows significant disc inclination generation. Thies et al. suggested that significant disc inclination and disc or planetary system shrinkage can generally be produced by the accretion of external gas material with a different angular momentum. We found that this condition can be fulfilled for a large range of gas mass and angular momentum. For all encounters, mass accretion from the secondary disc increases with decreasing mass of the secondary proto-star. Thus, higher disc inclinations can be attained for lower secondary stellar masses. Variations of the secondary disc's orientation relative to the orbital plane can alter the disc evolution significantly. The results taken together show that mass accretion can change the 3D disc orientation significantly resulting in strongly inclined discs. In combination with the gravitational interaction between the two star-disc systems, this scenario is relevant for explaining the formation of highly inclined discs that could later form misaligned planets.

  7. A simple framework for modelling the dependence of bulk Comptonization by turbulence on accretion disc parameters

    Science.gov (United States)

    Kaufman, J.; Blaes, O. M.; Hirose, S.

    2018-03-01

    Warm Comptonization models for the soft X-ray excess in AGN do not self-consistently explain the relationship between the Comptonizing medium and the underlying accretion disc. Because of this, they cannot directly connect the fitted Comptonization temperatures and optical depths to accretion disc parameters. Since bulk velocities exceed thermal velocities in highly radiation pressure dominated discs, in these systems bulk Comptonization by turbulence may provide a physical basis in the disc itself for warm Comptonization models. We model the dependence of bulk Comptonization on fundamental accretion disc parameters, such as mass, luminosity, radius, spin, inner boundary condition, and α. In addition to constraining warm Comptonization models, our model can help distinguish contributions from bulk Comptonization to the soft X-ray excess from those due to other physical mechanisms, such as absorption and reflection. By linking the time variability of bulk Comptonization to fluctuations in the disc vertical structure due to MRI turbulence, our results show that observations of the soft X-ray excess can be used to study disc turbulence in the radiation pressure dominated regime. Because our model connects bulk Comptonization to one dimensional vertical structure temperature profiles in a physically intuitive way, it will be useful for understanding this effect in future simulations run in new regimes.

  8. The effect of X-ray irradiation on the time-dependent behaviour of accretion discs with stochastic perturbations

    Science.gov (United States)

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

    2015-04-01

    The UV emission from X-ray binaries, is more likely to be produced by reprocessing of X-rays by the outer regions of an accretion disc. The structure of the outer disc may be altered due to the presence of X-ray irradiation and we discuss the physical regimes where this may occur and point out certain X-ray binaries where this effect may be important. The long-term X-ray variability of these sources is believed to be due to stochastic fluctuations in the outer disc, which propagate inwards giving rise to accretion rate variation in the X-ray-producing inner regions. The X-ray variability will induce structural variations in the outer disc which in turn may affect the inner accretion rate. To understand the qualitative behaviour of the disc in such a scenario, we adopt simplistic assumptions that the disc is fully ionized and is not warped. We develop and use a time-dependent global hydrodynamical code to study the effect of a sinusoidal accretion rate perturbation introduced at a specific radius. The response of the disc, especially the inner accretion rate, to such perturbations at different radii and with different time periods is shown. While we did not find any oscillatory or limit cycle behaviour, our results show that irradiation enhances the X-ray variability at time-scales corresponding to the viscous time-scales of the irradiated disc.

  9. Vortex survival in 3D self-gravitating accretion discs

    Science.gov (United States)

    Lin, Min-Kai; Pierens, Arnaud

    2018-04-01

    Large-scale, dust-trapping vortices may account for observations of asymmetric protoplanetary discs. Disc vortices are also potential sites for accelerated planetesimal formation by concentrating dust grains. However, in 3D discs vortices are subject to destructive `elliptic instabilities', which reduces their viability as dust traps. The survival of vortices in 3D accretion discs is thus an important issue to address. In this work, we perform shearing box simulations to show that disc self-gravity enhances the survival of 3D vortices, even when self-gravity is weak in the classic sense (e.g. with a Toomre Q ≃ 5). We find a 3D, self-gravitating vortex can grow on secular timescales in spite of the elliptic instability. The vortex aspect-ratio decreases as it strengthens, which feeds the elliptic instability. The result is a 3D vortex with a turbulent core that persists for ˜103 orbits. We find when gravitational and hydrodynamic stresses become comparable, the vortex may undergo episodic bursts, which we interpret as interaction between elliptic and gravitational instabilities. We estimate the distribution of dust particles in self-gravitating, turbulent vortices. Our results suggest large-scale vortices in protoplanetary discs are more easily observed at large radii.

  10. Beyond the standard model of the disc-line spectral profiles from black hole accretion discs

    Czech Academy of Sciences Publication Activity Database

    Sochora, Vjačeslav; Karas, Vladimír; Svoboda, Jiří; Dovčiak, Michal

    2014-01-01

    Roč. 54, č. 4 (2014), s. 301-304 ISSN 1210-2709 R&D Projects: GA ČR(CZ) GC13-00070J Institutional support: RVO:67985815 Keywords : accretion discs * black hole physics * galactic nuclei Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  11. Magnetized advective accretion flows: formation of magnetic barriers in Magnetically Arrested Discs

    Science.gov (United States)

    Mondal, Tushar; Mukhopadhyay, Banibrata

    2018-02-01

    We discuss the importance of large scale strong magnetic field in the removal of angular momentum outward, as well as the possible origin of different kinds of magnetic barrier in advective, geometrically thick, sub-Keplerian accretion flows around black holes. The origin of this large scale strong magnetic field near the event horizon is due to the advection of the magnetic flux by the accreting gas from the environment, say, the interstellar medium or a companion star, because of flux freezing. In this simplest vertically averaged, 1.5 -dimensional disc model, we choose the maximum upper limit of the magnetic field, which the disc around a black hole can sustain. In this so called magnetically arrested disc (MAD) model, the accreting gas either decelerates or faces the magnetic barrier near the event horizon by the accumulated magnetic field depending on the geometry. The magnetic barrier may knock the matter to infinity. We suggest that these types of flow are the building block to produce jets and outflows in the accreting system. We also find that in some cases, when matter is trying to go back to infinity after knocking the barrier, matter is prevented being escaped by the cumulative action of strong gravity and the magnetic tension, hence by another barrier. In this way, magnetic field can lock the matter in between these two barriers and it might be a possible explanation for the formation of episodic jet.

  12. Magnetized advective accretion flows: formation of magnetic barriers in magnetically arrested discs

    Science.gov (United States)

    Mondal, Tushar; Mukhopadhyay, Banibrata

    2018-05-01

    We discuss the importance of large-scale strong magnetic field in the removal of angular momentum outward, as well as the possible origin of different kinds of magnetic barrier in advective, geometrically thick, sub-Keplerian accretion flows around black holes. The origin of this large-scale strong magnetic field near the event horizon is due to the advection of the magnetic flux by the accreting gas from the environment, say, the interstellar medium or a companion star, because of flux freezing. In this simplest vertically averaged, 1.5-dimensional disc model, we choose the maximum upper limit of the magnetic field, which the disc around a black hole can sustain. In this so called magnetically arrested disc model, the accreting gas either decelerates or faces the magnetic barrier near the event horizon by the accumulated magnetic field depending on the geometry. The magnetic barrier may knock the matter to infinity. We suggest that these types of flow are the building block to produce jets and outflows in the accreting system. We also find that in some cases, when matter is trying to go back to infinity after knocking the barrier, matter is prevented being escaped by the cumulative action of strong gravity and the magnetic tension, hence by another barrier. In this way, magnetic field can lock the matter in between these two barriers and it might be a possible explanation for the formation of episodic jet.

  13. The gravitational microlens influence on X-ray spectral line generated by an AGN accretion disc

    Directory of Open Access Journals (Sweden)

    Popović L.Č.

    2001-01-01

    Full Text Available The influence of gravitational microlensing on the X-ray spectral line profiles originated from a relativistic accretion disc has been studied. Using a disc model, we show that microlensing can induce noticeable changes in the line shapes when the Einstein ring radius associated with the microlens is of a size comparable to that of the accretion disc. Taking into account the relatively small size of the X-ray accretion disc, we found that compact objects (of about a Solar mass which belong to the bulge of the host galaxy can produce significant changes in the X-ray line profile of AGN.

  14. The luminosity of particle beams from thick accretion discs

    International Nuclear Information System (INIS)

    Narayan, R.; Nityananda, R.; Wiita, P.J.

    1983-01-01

    The interaction of the radiation produced in the funnels of thick, highly luminous accretion discs with the walls of these funnels is investigated. Some processes not considered in an earlier discussion have been included. The turbulent mixing of the surface layer with deeper regions acts to reduce the luminosity associated with outflowing matter. The modification of the radiation field by the moving walls is also important. It is found, for the specific funnel geometry studied, corresponding to a radiation luminosity of 8.5 times the Eddington limit Lsub(E), that up to 1.5 Lsub(E) can be carried away as a particle beam, even for an optically thin funnel. This particle luminosity is sensitive to the sound velocity and the mixing efficiency in the walls. (author)

  15. Luminosity limits for funnels in thick accretion discs

    International Nuclear Information System (INIS)

    Nityananda, R.; Narayan, R.

    1982-01-01

    A narrow, highly luminous funnel in a thick accretion disc is a common feature of many models for active galactic nuclei. The constraints on the luminosity imposed by the effects of radiation forces on the funnel are examined. The treatment allows properly for the irradiation of any part of the funnel by the rest, an important effect for this problem. It is found that the maximum luminosity of a funnel of small semi-angle phi is reduced below the Eddington limit Lsub(E) by a factor phi 2 if the funnel is to be in strict equilibrium. Even with allowance for flow induced viscous stresses, the luminosity cannot exceed of the order of Lsub(E)phi. In contrast, current models have luminosities of the order of Lsub(E)/phi. It is shown that the resulting large unbalanced forces at the funnel surface cause a significant outflow of matter which should be incorporated in the model for consistency. These results do not depend on the detailed angular momentum distribution over the disc surface but only on the funnel geometry. (author)

  16. Accretion-disc precession in UX Ursae Majoris

    Science.gov (United States)

    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.

  17. In situ accretion of gaseous envelopes on to planetary cores embedded in evolving protoplanetary discs

    Science.gov (United States)

    Coleman, Gavin A. L.; Papaloizou, John C. B.; Nelson, Richard P.

    2017-09-01

    The core accretion hypothesis posits that planets with significant gaseous envelopes accreted them from their protoplanetary discs after the formation of rocky/icy cores. Observations indicate that such exoplanets exist at a broad range of orbital radii, but it is not known whether they accreted their envelopes in situ, or originated elsewhere and migrated to their current locations. We consider the evolution of solid cores embedded in evolving viscous discs that undergo gaseous envelope accretion in situ with orbital radii in the range 0.1-10 au. Additionally, we determine the long-term evolution of the planets that had no runaway gas accretion phase after disc dispersal. We find the following. (I) Planets with 5 M⊕ cores never undergo runaway accretion. The most massive envelope contained 2.8 M⊕ with the planet orbiting at 10 au. (II) Accretion is more efficient on to 10 M⊕ and 15 M⊕ cores. For orbital radii ap ≥ 0.5 au, 15 M⊕ cores always experienced runaway gas accretion. For ap ≥ 5 au, all but one of the 10 M⊕ cores experienced runaway gas accretion. No planets experienced runaway growth at ap = 0.1 au. (III) We find that, after disc dispersal, planets with significant gaseous envelopes cool and contract on Gyr time-scales, the contraction time being sensitive to the opacity assumed. Our results indicate that Hot Jupiters with core masses ≲15 M⊕ at ≲0.1 au likely accreted their gaseous envelopes at larger distances and migrated inwards. Consistently with the known exoplanet population, super-Earths and mini-Neptunes at small radii during the disc lifetime, accrete only modest gaseous envelopes.

  18. X-ray reflection in oxygen-rich accretion discs of ultracompact X-ray binaries

    DEFF Research Database (Denmark)

    Madej, O. K.; Garcia, Jeronimo; Jonker, P. G.

    2014-01-01

    . The donor star in these sources is a carbon-oxygen or oxygen-neon-magnesium white dwarf. Hence, the accretion disc is enriched with oxygen which makes the O viii Ly alpha line particularly strong. Modelling the X-ray reflection off a carbon- and oxygen-enriched, hydrogen- and helium-poor disc with models...

  19. Estimating gas accretion in disc galaxies using the Kennicutt-Schmidt law

    NARCIS (Netherlands)

    Fraternali, Filippo; Tomassetti, Matteo

    2012-01-01

    We show how the existence of a relation between the star formation rate (SFR) and the gas density, i.e. the KennicuttSchmidt law, implies a continuous accretion of fresh gas from the environment into the discs of spiral galaxies. We present a method to derive the gas infall rate in a galaxy disc as

  20. A Laboratory Plasma Experiment for Studying Magnetic Dynamics of Accretion Discs and Jets

    OpenAIRE

    Hsu, S. C.; Bellan, P. M.

    2002-01-01

    This work describes a laboratory plasma experiment and initial results which should give insight into the magnetic dynamics of accretion discs and jets. A high-speed multiple-frame CCD camera reveals images of the formation and helical instability of a collimated plasma, similar to MHD models of disc jets, and also plasma detachment associated with spheromak formation, which may have relevance to disc winds and flares. The plasmas are produced by a planar magnetized coaxial gun. The resulting...

  1. Modeling the response of a standard accretion disc to stochastic viscous fluctuations

    Science.gov (United States)

    Ahmad, Naveel; Misra, Ranjeev; Iqbal, Naseer; Maqbool, Bari; Hamid, Mubashir

    2018-01-01

    The observed variability of X-ray binaries over a wide range of time-scales can be understood in the framework of a stochastic propagation model, where viscous fluctuations at different radii induce accretion rate variability that propagate inwards to the X-ray producing region. The scenario successfully explains the power spectra, the linear rms-flux relation as well as the time-lag between different energy photons. The predictions of this model have been obtained using approximate analytical solutions or empirically motivated models which take into account the effect of these propagating variability on the radiative process of complex accretion flows. Here, we study the variation of the accretion rate due to such viscous fluctuations using a hydro-dynamical code for the standard geometrically thin, gas pressure dominated α-disc with a zero torque boundary condition. Our results confirm earlier findings that the time-lag between a perturbation and the resultant inner accretion rate variation depends on the frequency (or time-period) of the perturbation. Here we have quantified that the time-lag tlag ∝f-0.54 , for time-periods less than the viscous time-scale of the perturbation radius and is nearly constant otherwise. This, coupled with radiative process would produce the observed frequency dependent time-lag between different energy bands. We also confirm that if there are random Gaussian fluctuations of the α-parameter at different radii, the resultant inner accretion rate has a power spectrum which is a power-law.

  2. Accreting transition discs with large cavities created by X-ray photoevaporation in C and O depleted discs

    Science.gov (United States)

    Ercolano, Barbara; Weber, Michael L.; Owen, James E.

    2018-01-01

    Circumstellar discs with large dust depleted cavities and vigorous accretion on to the central star are often considered signposts for (multiple) giant planet formation. In this Letter, we show that X-ray photoevaporation operating in discs with modest (factors 3-10) gas-phase depletion of carbon and oxygen at large radii ( > 15 au) yields the inner radius and accretion rates for most of the observed discs, without the need to invoke giant planet formation. We present one-dimensional viscous evolution models of discs affected by X-ray photoevaporation assuming moderate gas-phase depletion of carbon and oxygen, well within the range reported by recent observations. Our models use a simplified prescription for scaling the X-ray photoevaporation rates and profiles at different metallicity, and our quantitative result depends on this scaling. While more rigorous hydrodynamical modelling of mass-loss profiles at low metallicities is required to constrain the observational parameter space that can be explained by our models, the general conclusion that metal sequestering at large radii may be responsible for the observed diversity of transition discs is shown to be robust. Gap opening by giant planet formation may still be responsible for a number of observed transition discs with large cavities and very high accretion rate.

  3. The disappearance and reformation of the accretion disc during a low state of FO Aquarii

    Science.gov (United States)

    Hameury, J.-M.; Lasota, J.-P.

    2017-09-01

    Context. FO Aquarii, an asynchronous magnetic cataclysmic variable (intermediate polar) went into a low state in 2016, from which it slowly and steadily recovered without showing dwarf nova outbursts. This requires explanation since in a low state, the mass-transfer rate is in principle too low for the disc to be fully ionised and the disc should be subject to the standard thermal and viscous instability observed in dwarf novae. Aims: We investigate the conditions under which an accretion disc in an intermediate polar could exhibit a luminosity drop of two magnitudes in the optical band without showing outbursts. Methods: We use our numerical code for the time evolution of accretion discs, including other light sources from the system (primary, secondary, hot spot). Results: We show that although it is marginally possible for the accretion disc in the low state to stay on the hot stable branch, the required mass-transfer rate in the normal state would then have to be extremely high, of the order of 1019 g s-1 or even larger. This would make the system so intrinsically bright that its distance should be much larger than allowed by all estimates. We show that observations of FO Aqr are well accounted for by the same mechanism that we have suggested as explaining the absence of outbursts during low states of VY Scl stars: during the decay, the magnetospheric radius exceeds the circularisation radius, so that the disc disappears before it enters the instability strip for dwarf nova outbursts. Conclusions: Our results are unaffected, and even reinforced, if accretion proceeds both via the accretion disc and directly via the stream during some intermediate stages; the detailed process through which the disc disappears still requires investigation.

  4. Chemical enrichment of giant planets and discs due to pebble drift

    Science.gov (United States)

    Booth, Richard A.; Clarke, Cathie J.; Madhusudhan, Nikku; Ilee, John D.

    2017-08-01

    Chemical compositions of giant planets provide a means to constrain how and where they form. Traditionally, super-stellar elemental abundances in giant planets were thought to be possible due to accretion of metal-rich solids. Such enrichments are accompanied by oxygen-rich compositions (I.e. C/O below the disc's value, assumed to be solar, C/O = 0.54). Without solid accretion, the planets are expected to have sub-solar metallicity, but high C/O ratios. This arises because the solids are dominated by oxygen-rich species, e.g. H2O and CO2, which freeze out in the disc earlier than CO, leaving the gas metal poor but carbon rich. Here we demonstrate that super-solar metallicities can be achieved by gas accretion alone when growth and radial drift of pebbles are considered in protoplanetary discs. Through this mechanism, planets may simultaneously acquire super-solar metallicities and super-solar C/O ratios. This happens because the pebbles transport volatile species inwards as they migrate through the disc, enriching the gas at snow lines where the volatiles sublimate. Furthermore, the planet's composition can be used to constrain where it formed. Since high C/H and C/O ratios cannot be created by accreting solids, it may be possible to distinguish between formation via pebble accretion and planetesimal accretion by the level of solid enrichment. Finally, we expect that Jupiter's C/O ratio should be near or above solar if its enhanced carbon abundance came through accreting metal-rich gas. Thus, Juno's measurement of Jupiter's C/O ratio should determine whether Jupiter accreted its metals from carbon-rich gas or oxygen-rich solids.

  5. Transient jet formation and state transitions from large-scale magnetic reconnection in black hole accretion discs

    NARCIS (Netherlands)

    Dexter, J.; McKinney, J.C.; Markoff, S.; Tchekhovskoy, A.

    2014-01-01

    Magnetically arrested accretion discs (MADs), where the magnetic pressure in the inner disc is dynamically important, provide an alternative mechanism for regulating accretion to what is commonly assumed in black hole systems. We show that a global magnetic field inversion in the MAD state can

  6. Spectral properties of the accretion discs around rotating black holes

    Indian Academy of Sciences (India)

    Samir Mandal

    2018-02-10

    Feb 10, 2018 ... attention has also been paid to the variation in energy spectral index with Kerr parameter and accretion rate. We find that spectral index .... entropy generation equation (or equation of state). In the absence of dissipation in the ..... the study was confined around a stationary BH. Here, we intend to see the ...

  7. Eclipsing the innermost accretion disc regions in AGN

    Czech Academy of Sciences Publication Activity Database

    Sanfrutos, M.; Miniutti, G.; Dovčiak, Michal; Agis-Gonzalez, B.

    2016-01-01

    Roč. 337, 4-5 (2016), s. 546-551 ISSN 0004-6337 Institutional support: RVO:67985815 Keywords : accretion disks * black hole physics * relativistic effects Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 0.916, year: 2016

  8. Turbulence in Accretion Discs. The Global Baroclinic Instability

    Science.gov (United States)

    Klahr, Hubert; Bodenheimer, Peter

    The transport of angular momentum away from the central object is a sufficient condition for a protoplanetary disk to accrete matter onto the star and spin it down. Magnetic fields cannot be of importance for this process in a large part of the cold and dusty disk where the planets supposedly form. Our new hypothesis on the angular momentum transport based on radiation hydro simulations is as follows: We present the global baroclinic instability as a source for vigorous turbulence leading to angular momentum transport in Keplerian accretion disks. We show by analytical considerations and three-dimensional radiation hydro simulations that, in particular, protoplanetary disks have a negative radial entropy gradient, which makes them baroclinic. Two-dimensional numerical simulations show that this baroclinic flow is unstable and produces turbulence. These findings are currently tested for numerical effects by performing barotropic simulations which show that imposed turbulence rapidly decays. The turbulence in baroclinic disks draws energy from the background shear, transports angular momentum outward and creates a radially inward bound accretion of matter, thus forming a self consistent process. Gravitational energy is transformed into turbulent kinetic energy, which is then dissipated, as in the classical accretion paradigm. We measure accretion rates in 2D and 3D simulations of dot M= - 10-9 to -10-7 Msolar yr-1 and viscosity parameters of α = 10-4 - 10-2, which fit perfectly together and agree reasonably with observations. The turbulence creates pressure waves, Rossby waves, and vortices in the (r-φ) plane of the disk. We demonstrate in a global simulation that these vortices tend to form out of little background noise and to be long-lasting features, which have already been suggested to lead to the formation of planets.

  9. The ephemeris and variations of the accretion disc radius in IP Pegasi

    International Nuclear Information System (INIS)

    Wood, J.H.; Robinson, E.L.

    1989-01-01

    We present timings of 37 previously unpublished eclipses of the dwarf nova IP Pegasi, obtained in 1986 through to 1988, and combine these with earlier published timings in order to update the orbital ephemeris and to examine the behaviour of the accretion disc radius through the outburst cycle. (author)

  10. Radio emission from Sgr A*: pulsar transits through the accretion disc

    Science.gov (United States)

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

    2017-06-01

    Radiatively inefficient accretion flow models have been shown to accurately account for the spectrum and luminosity observed from Sgr A* in the X-ray regime down to mm wavelengths. However, observations at a few GHz cannot be explained by thermal electrons alone but require the presence of an additional non-thermal particle population. Here, we propose a model for the origin of such a population in the accretion flow via means of a pulsar orbiting the supermassive black hole in our Galaxy. Interactions between the relativistic pulsar wind with the disc lead to the formation of a bow shock in the wind. During the pulsar's transit through the accretion disc, relativistic pairs, accelerated at the shock front, are injected into the disc. The radio-emitting particles are long lived and remain within the disc long after the pulsar's transit. Periodic pulsar transits through the disc result in regular injection episodes of non-thermal particles. We show that for a pulsar with spin-down luminosity Lsd ˜ 3 × 1035 erg s-1 and a wind Lorentz factor of γw ˜ 104 a quasi-steady synchrotron emission is established with luminosities in the 1-10 GHz range comparable to the observed one.

  11. BEYOND THE STANDARD MODEL OF THE DISC–LINE SPECTRAL PROFILES FROM BLACK HOLE ACCRETION DISCS

    Directory of Open Access Journals (Sweden)

    Vjaceslav Sochora

    2014-08-01

    Full Text Available The strong gravitational field of a black hole has distinct effects on the observed profile of a spectral line from an accretion disc near a black hole. The observed profile of the spectral line is broadened and skewed by a fast orbital motion and redshifted by a gravitational field. These effects can help us to constrain the parameters of a system with a black hole, both in active galactic nuclei and in a stellar-mass black hole. Here we explore the fact that an accretion disc emission can be mathematically imagined as a superposition of radiating accretion rings that extend from the inner edge to the outer rim of the disc, with some radially varying emissivity. In our work, we show that a characteristic double-horn profile of several radially confined (relatively narrow accretion rings or belts could be recognized by the planned instruments onboard future satellites (such as the proposed ESA Large Observatory for X-ray Timing.

  12. Optically thin core accretion: how planets get their gas in nearly gas-free discs

    Science.gov (United States)

    Lee, Eve J.; Chiang, Eugene; Ferguson, Jason W.

    2018-05-01

    Models of core accretion assume that in the radiative zones of accreting gas envelopes, radiation diffuses. But super-Earths/sub-Neptunes (1-4 R⊕, 2-20 M⊕) point to formation conditions that are optically thin: their modest gas masses are accreted from short-lived and gas-poor nebulae reminiscent of the transparent cavities of transitional discs. Planetary atmospheres born in such environments can be optically thin to both incident starlight and internally generated thermal radiation. We construct time-dependent models of such atmospheres, showing that super-Earths/sub-Neptunes can accrete their ˜1 per cent-by-mass gas envelopes, and super-puffs/sub-Saturns their ˜20 per cent-by-mass envelopes, over a wide range of nebular depletion histories requiring no fine tuning. Although nascent atmospheres can exhibit stratospheric temperature inversions affected by atomic Fe and various oxides that absorb strongly at visible wavelengths, the rate of gas accretion remains controlled by the radiative-convective boundary (rcb) at much greater pressures. For dusty envelopes, the temperature at the rcb Trcb ≃ 2500 K is still set by H2 dissociation; for dust-depleted envelopes, Trcb tracks the temperature of the visible or thermal photosphere, whichever is deeper, out to at least ˜5 au. The rate of envelope growth remains largely unchanged between the old radiative diffusion models and the new optically thin models, reinforcing how robustly super-Earths form as part of the endgame chapter in disc evolution.

  13. Quasi-periodic oscillations and the global modes of relativistic, MHD accretion discs

    Science.gov (United States)

    Dewberry, Janosz W.; Latter, Henrik N.; Ogilvie, Gordon I.

    2018-02-01

    The high-frequency quasi-periodic oscillations (HFQPOs) that punctuate the light curves of X-ray binary systems present a window onto the intrinsic properties of stellar-mass black holes and hence a testbed for general relativity. One explanation for these features is that relativistic distortion of the accretion disc's differential rotation creates a trapping region in which inertial waves (r-modes) might grow to observable amplitudes. Local analyses, however, predict that large-scale magnetic fields push this trapping region to the inner disc edge, where conditions may be unfavorable for r-mode growth. We revisit this problem from a pseudo-Newtonian but fully global perspective, deriving linearized equations describing a relativistic, magnetized accretion flow, and calculating normal modes with and without vertical density stratification. In an unstratified model, the choice of vertical wavenumber determines the extent to which vertical magnetic fields drive the r-modes toward the inner edge. In a global model fully incorporating density stratification, we confirm that this susceptibility to magnetic fields depends on disc thickness. Our calculations suggest that in thin discs, r-modes may remain independent of the inner disc edge for vertical magnetic fields with plasma betas as low as β ≈ 100 - 300. We posit that the appearance of r-modes in observations may be more determined by a competition between excitation and damping mechanisms near the ISCO than the modification of the trapping region by magnetic fields.

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

    DEFF Research Database (Denmark)

    Pessah, Martin Elias; Chan, Chi-kwan; Psaltis, Dimitrios

    2006-01-01

    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 scale-height) 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...

  15. Viscous driving of global oscillations in accretion discs around black holes

    Czech Academy of Sciences Publication Activity Database

    Miranda, R.; Horák, Jiří; Lai, D.

    2015-01-01

    Roč. 446, č. 1 (2015), s. 240-253 ISSN 0035-8711 R&D Projects: GA MŠk(CZ) LH14049 Grant - others:Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100031202 Institutional support: RVO:67985815 Keywords : accretion discs * hydrodynamics * waves Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.952, year: 2015

  16. Dust inflated accretion disc as the origin of the broad line region in active galactic nuclei

    Science.gov (United States)

    Baskin, Alexei; Laor, Ari

    2018-02-01

    The broad line region (BLR) in active galactic nuclei (AGNs) is composed of dense gas (˜1011 cm-3) on sub-pc scale, which absorbs about 30 per cent of the ionizing continuum. The outer size of the BLR is likely set by dust sublimation, and its density by the incident radiation pressure compression (RPC). But, what is the origin of this gas, and what sets its covering factor (CF)? Czerny & Hryniewicz (2011) suggested that the BLR is a failed dusty wind from the outer accretion disc. We explore the expected dust properties, and the implied BLR structure. We find that graphite grains sublimate only at T ≃ 2000 K at the predicted density of ˜1011 cm-3, and therefore large graphite grains (≥0.3 μm) survive down to the observed size of the BLR, RBLR. The dust opacity in the accretion disc atmosphere is ˜50 times larger than previously assumed, and leads to an inflated torus-like structure, with a predicted peak height at RBLR. The illuminated surface of this torus-like structure is a natural place for the BLR. The BLR CF is mostly set by the gas metallicity, the radiative accretion efficiency, a dynamic configuration and ablation by the incident optical-UV continuum. This model predicts that the BLR should extend inwards of RBLR to the disc radius where the surface temperature is ≃2000 K, which occurs at Rin ≃ 0.18RBLR. The value of Rin can be tested by reverberation mapping of the higher ionization lines, predicted by RPC to peak well inside RBLR. The dust inflated disc scenario can also be tested based on the predicted response of RBLR and the CF to changes in the AGN luminosity and accretion rate.

  17. Erratum: Spiral structure in the accretion disc of the binary IP Pegasi

    Science.gov (United States)

    Steeghs, D.; Harlaftis, E. T.; Horne, Keith

    1998-05-01

    The paper `Spiral structure in the accretion disc of the binary IP Pegasi' was published in Mon. Not. R. Astron. Soc. 290, L28-L32 (1997). Figs 1 and 2 of the paper (grey-scale images) did not reproduce well, and are reprinted here (Fig. 1 overleaf). Colour versions of the images are available on the World Wide Web:http://www-star.st-and.ac.uk/^~ds10/spirals.html

  18. Supersonic turbulence, filamentary accretion and the rapid assembly of massive stars and discs

    Science.gov (United States)

    Banerjee, Robi; Pudritz, Ralph E.; Anderson, Dave W.

    2006-12-01

    We present a detailed computational study of the assembly of protostellar discs and massive stars in molecular clouds with supersonic turbulence. We follow the evolution of large-scale filamentary structures in a cluster-forming clump down to protostellar length-scales by means of very highly resolved, 3D adaptive mesh refined (AMR) simulations, and show how accretion discs and massive stars form in such environments. We find that an initially elongated cloud core which has a slight spin from oblique shocks collapses first to a filament and later develops a turbulent disc close to the centre of the filament. The continued large-scale flow that shocks with the filament maintains the high density and pressure within it. Material within the cooling filament undergoes gravitational collapse and an outside-in assembly of a massive protostar. Our simulations show that very high mass accretion rates of up to 10-2Msolaryr-1 and high, supersonic, infall velocities result from such filamentary accretion. Accretion at these rates is higher by an order of magnitude than those found in semi-analytic studies, and can quench the radiation field of a growing massive young star. Our simulations include a comprehensive set of the important chemical and radiative processes such as cooling by molecular line emission, gas-dust interaction and radiative diffusion in the optically thick regime, as well as H2 formation and dissociation. Therefore, we are able to probe, for the first time, the relevant physical phenomena on all scales from those characterizing the clump down to protostellar core.

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

    Science.gov (United States)

    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 ∼10 8  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 × 10 33  erg s -1 for a stellar mass-loss rate, disc number density, and thermal pressure strength of [Formula: see text], n d  = 10 5  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.

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

    Czech Academy of Sciences Publication Activity Database

    Horák, Jiří; Lai, D.

    2013-01-01

    Roč. 434, č. 4 (2013), s. 2761-2771 ISSN 0035-8711 R&D Projects: GA MŠk ME09036; GA ČR(CZ) GAP209/11/2004 Grant - others:NASA(US) NNX12AF85G; NSF(US) AST-1008245; NSF(US) AST-1211061; Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100031202 Institutional support: RVO:67985815 Keywords : accretion discs * hydrodynamics * X-ray binaries Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.226, year: 2013

  1. Fate of an accretion disc around a black hole when both the viscosity and dark energy is in effect

    Energy Technology Data Exchange (ETDEWEB)

    Dutta, Sandip; Biswas, Ritabrata [The University of Burdwan, Department of Mathematics, Burdwan, West Bengal (India)

    2017-10-15

    This paper deals with the viscous accretion flow of a modified Chaplygin gas towards a black hole as the central gravitating object. A modified Chaplygin gas is a particular type of dark energy model which mimics of radiation era to phantom era depending on the different values of its parameters. We compare the dark energy accretion with the flow of adiabatic gas. An accretion disc flowing around a black hole is an example of a transonic flow. To construct the model, we consider three components of the Navier-Stokes equation, the equation of continuity and the modified Chaplygin gas equation of state. As a transonic flow passes through the sonic point, the velocity gradient being apparently singular there, it gives rise to two flow branches: one in-falling, the accretion and the other outgoing, the wind. We show that the wind curve is stronger and the wind speed reaches that of light at a finite distance from the black hole when dark energy is considered. Besides, if we increase the viscosity, the accretion disc is shortened in radius. These two processes acting together make the system deviate much from the adiabatic accretion case. It shows a weakening process for the accretion procedure by the work of the viscous system influencing both the angular momentum transport and the repulsive force of the modified Chaplygin gas. (orig.)

  2. [Efficacy of percutaneous laser disc decompression for radiculalgia due to lumbar disc hernia (149 patients)].

    Science.gov (United States)

    Morelet, Aude; Boyer, François; Vitry, Fabien; Ackah-Miezan, Stanley; Berquet, Renaud; Langlois, Sandrine; Brochot, Pascal; Breidt, Damien; Eschard, Jean-Paul; Etienne, Jean-Claude

    2007-11-01

    To assess the efficacy of percutaneous laser disc decompression for patients with radicular pain due to lumbar disc hernia and to identify factors that may predict outcome. The study included all patients treated with percutaneous laser disc decompression from May 2003 through May 2005 at Reims University Hospital and the Courlancy Clinic of Reims. Each patient had previous undergone at least six weeks of conventional medical treatment. The same technique, with either a laser diode or Nd: YAG, was used under endoscopic control and with neuroleptanalgesia. They were seen at 1, 3, 6 and 12 months. The principal evaluation criteria were the course of radicular pain, return to work, and need for surgery. We reexamined 149 patients 1 month after the procedure, 135 after 3 months, 102 after 6 months and 59 a year after the procedure. At a month after surgery, radicular pain had decreased by at least half, and sometimes even completely disappeared in 63.1% of patients at 1 month, 66.6% at 3 months, 73.5% at 6 months, and 83.1% at 12 months, while 24%, 50,4%, 61.2%, and 67.3%, respectively, had returned to work. No patient had serious complications. Finally, 45 of the 149 (30.2%) patients chose to have a traditional surgical procedure after percutaneous laser disc decompression. Percutaneous laser disc decompression is effective, noninvasive and well tolerated for patients with radicular pain due to lumbar disc hernia.

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

    Science.gov (United States)

    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.

  4. Papaloizou-Pringle instability suppression by the magnetorotational instability in relativistic accretion discs

    Science.gov (United States)

    Bugli, M.; Guilet, J.; Müller, E.; Del Zanna, L.; Bucciantini, N.; Montero, P. J.

    2018-03-01

    Geometrically thick tori with constant specific angular momentum have been widely used in the last decades to construct numerical models of accretion flows on to black holes. Such discs are prone to a global non-axisymmetric hydrodynamic instability, known as Papaloizou-Pringle instability (PPI), which can redistribute angular momentum and also lead to an emission of gravitational waves. It is, however, not clear yet how the development of the PPI is affected by the presence of a magnetic field and by the concurrent development of the magnetorotational instability (MRI). We present a numerical analysis using three-dimensional GRMHD simulations of the interplay between the PPI and the MRI considering, for the first time, an analytical magnetized equilibrium solution as initial condition. In the purely hydrodynamic case, the PPI selects as expected the large-scale m = 1 azimuthal mode as the fastest growing and non-linearly dominant mode. However, when the torus is threaded by a weak toroidal magnetic field, the development of the MRI leads to the suppression of large-scale modes and redistributes power across smaller scales. If the system starts with a significantly excited m = 1 mode, the PPI can be dominant in a transient phase, before being ultimately quenched by the MRI. Such dynamics may well be important in compact star mergers and tidal disruption events.

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

    Science.gov (United States)

    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.

  6. Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers

    Science.gov (United States)

    Wu, Meng-Ru; Fernández, Rodrigo; Martínez-Pinedo, Gabriel; Metzger, Brian D.

    2016-12-01

    We consider r-process nucleosynthesis in outflows from black hole accretion discs formed in double neutron star and neutron star-black hole mergers. These outflows, powered by angular momentum transport processes and nuclear recombination, represent an important - and in some cases dominant - contribution to the total mass ejected by the merger. Here we calculate the nucleosynthesis yields from disc outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. We find that outflows produce a robust abundance pattern around the second r-process peak (mass number A ˜ 130), independent of model parameters, with significant production of A spike at A = 132 that is absent in the Solar system r-process distribution. The spike arises from convection in the disc and depends on the treatment of nuclear heating in the simulations. We conclude that disc outflows provide an important - and perhaps dominant - contribution to the r-process yields of compact binary mergers, and hence must be included when assessing the contribution of these systems to the inventory of r-process elements in the Galaxy.

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

    Science.gov (United States)

    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

  8. Determination of the turbulent parameter in accretion discs: effects of self-irradiation in 4U 1543-47 during the 2002 outburst

    Science.gov (United States)

    Lipunova, G. V.; Malanchev, K. L.

    2017-07-01

    We investigate the viscous evolution of the accretion disc in 4U 1543-47, a black hole binary system, during the first 30 d after the peak of the 2002 burst by comparing the observed and theoretical accretion rate evolution \\dot{M}(t). The observed \\dot{M}(t) is obtained from spectral modelling of the archival Proportional Counter Array aboard the RXTE observatory (RXTE/PCA) data. Different scenarios of disc decay evolution are possible depending on a degree of self-irradiation of the disc by the emission from its centre. If the self-irradiation, which is parametrized by factor Cirr, had been as high as ˜5 × 10-3, then the disc would have been completely ionized up to the tidal radius and the short time of the decay would have required the turbulent parameter α ˜ 3. We find that the shape of the \\dot{M}(t) curve is much better explained in a model with a shrinking high-viscosity zone. If Cirr ≈ (2-3) × 10-4, the resulting α lie in the interval 0.5-1.5 for the black hole masses in the range 6-10 M⊙, while the radius of the ionized disc is variable and controlled by irradiation. For very weak irradiation, Cirr public 1D code freddi to model the viscous evolution of an accretion disc. Analytic approximations are derived to estimate α in X-ray novae using \\dot{M}(t).

  9. Accretion funnels onto weakly magnetized young stars

    NARCIS (Netherlands)

    Bessolaz, N.; Zanni, C.; Ferreira, J.; Keppens, R.; Bouvier, J.

    2008-01-01

    Aims. We re-examine the conditions required to steadily deviate an accretion flow from a circumstellar disc into a magnetospheric funnel flow onto a slow rotating young forming star. Methods. New analytical constraints on the formation of accretion funnels flows due to the presence of a dipolar

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

    Science.gov (United States)

    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.

  11. Time dependent spectrum of an X-ray irradiated accretion disc with stochastic perturbations

    Science.gov (United States)

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

    2016-07-01

    The X-rays emitted by the inner regions of the accretion disk induce structural changes in the outer regions of the disk. We study here how the effective temperature and hence the corresponding spectrum of the disk is altered by stochastic perturbations in the outer regions and thereby try to study the long term variability which has been observed in some X-ray binaries. We use a time dependent global hydrodynamic code to study the variations in the effective temperature of the disk in response to sinusoidal accretion rate perturbations introduced at different radii and with different time periods. To quantify the results, we calculate the root mean square effective temperature at different radii and the root mean square flux at different frequencies. From our calculations of the time-lags in accretion rate, effective temperature and the different frequencies, we find that the time-lags in presence of X-ray irradiation is significantly smaller than the expected viscous time-scale.

  12. The Effects of High Density on the X-ray Spectrum Reflected from Accretion Discs Around Black Holes

    Science.gov (United States)

    Garcia, Javier A.; Fabian, Andrew C.; Kallman, Timothy R.; Dauser, Thomas; Parker, Micahel L.; McClintock, Jeffrey E.; Steiner, James F.; Wilms, Jorn

    2016-01-01

    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 (xi), which is the ratio of the incident flux to the gas density. The density is typically fixed at n(sub e) = 10(exp 15) per cu cm. Motivated by observations, we consider higher densities in the calculation of the reflected spectrum. We show by computing model spectra for n(sub e) approximately greater than 10(exp 17) per cu cm that high-density effects significantly modify reflection spectra. The main effect is to boost the thermal continuum at energies 2 approximately less than 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.

  13. Surgical techniques for sciatica due to herniated disc, a systematic review

    NARCIS (Netherlands)

    Jacobs, Wilco C H; Arts, Mark P.; van Tulder, Maurits W; Rubinstein, Sidney M; van Middelkoop, Marienke; Ostelo, Raymond W; Verhagen, Arianne P; Koes, Bart W; Peul, Wilco C.

    2012-01-01

    INTRODUCTION: Disc herniation with sciatica accounts for five percent of low-back disorders but is one of the most common reasons for spine surgery. The goal of this study was to update the Cochrane review on the effect of surgical techniques for sciatica due to disc herniation, which was last

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  16. Bowen emission from Aquila X-1: evidence for multiple components and constraint on the accretion disc vertical structure

    Science.gov (United States)

    Jiménez-Ibarra, F.; Muñoz-Darias, T.; Wang, L.; Casares, J.; Mata Sánchez, D.; Steeghs, D.; Armas Padilla, M.; Charles, P. A.

    2018-03-01

    We present a detailed spectroscopic study of the optical counterpart of the neutron star X-ray transient Aquila X-1 during its 2011, 2013 and 2016 outbursts. We use 65 intermediate resolution GTC-10.4 m spectra with the aim of detecting irradiation-induced Bowen blend emission from the donor star. While Gaussian fitting does not yield conclusive results, our full phase coverage allows us to exploit Doppler mapping techniques to independently constrain the donor star radial velocity. By using the component N III 4640.64/4641.84 Å, we measure Kem = 102 ± 6 km s-1. This highly significant detection (≳13σ) is fully compatible with the true companion star radial velocity obtained from near-infrared spectroscopy during quiescence. Combining these two velocities we determine, for the first time, the accretion disc opening angle and its associated error from direct spectroscopic measurements and detailed modelling, obtaining α = 15.5 ^{+ 2.5}_{-5} deg. This value is consistent with theoretical work if significant X-ray irradiation is taken into account and is important in the light of recent observations of GX339-4, where discrepant results were obtained between the donor's intrinsic radial velocity and the Bowen-inferred value. We also discuss the limitations of the Bowen technique when complete phase coverage is not available.

  17. Deformation of the Galactic Centre stellar cusp due to the gravity of a growing gas disc

    Science.gov (United States)

    Kaur, Karamveer; Sridhar, S.

    2018-03-01

    The nuclear star cluster surrounding the massive black hole at the Galactic Centre consists of young and old stars, with most of the stellar mass in an extended, cuspy distribution of old stars. The compact cluster of young stars was probably born in situ in a massive accretion disc around the black hole. We investigate the effect of the growing gravity of the disc on the orbits of the old stars, using an integrable model of the deformation of a spherical star cluster with anisotropic velocity dispersions. A formula for the perturbed phase space distribution function is derived using linear theory, and new density and surface density profiles are computed. The cusp undergoes a spheroidal deformation with the flattening increasing strongly at smaller distances from the black hole; the intrinsic axis ratio ˜0.8 at ˜0.15 pc. Stellar orbits are deformed such that they spend more time near the disc plane and sample the dense inner parts of the disc; this could result in enhanced stripping of the envelopes of red giant stars. Linear theory accounts only for orbits whose apsides circulate. The non-linear theory of adiabatic capture into resonance is needed to understand orbits whose apsides librate. The mechanism is a generic dynamical process, and it may be common in galactic nuclei.

  18. Conus medullaris syndrome due to an intradural disc herniation: A case report

    Directory of Open Access Journals (Sweden)

    Chaudhary Kshitij

    2008-01-01

    Full Text Available A 70-year-old male patient developed acute paraplegia due to conus medullaris compression secondary to extrusion of D12-L1 disc. After negative epidural examination intraoperatively, a durotomy was performed and an intradural disc fragment was excised. Patient did not regain ambulatory status at two-year follow-up. Intraoperative finding of negative extradural compression, tense swollen dura and CSF leak from ventral dura should alert the surgeon for the possibility of intradural disc herniation. A routine preoperative MRI is misleading and a high index of suspicion helps to avoid a missed diagnosis.

  19. Lumbar radiculopathy due to unilateral facet hypertrophy following lumbar disc hernia operation: a case report.

    Science.gov (United States)

    Kökeş, Fatih; Günaydin, Ahmet; Aciduman, Ahmet; Kalan, Mehmet; Koçak, Halit

    2007-10-01

    To present a radiculopathy case due to unilateral facet hypertrophy developing three years after a lumbar disc hernia operation. A fifty two-year-old female patient, who had been operated on for a left L5-S1 herniated lumbar disc three years ago, was hospitalized and re-operated with a diagnosis of unilateral facet hypertrophy. She had complaints of left leg pain and walking restrictions for the last six months. Left Straight Leg Raising test was positive at 40 degrees , left ankle dorsiflexion muscle strength was 4/5, left Extensor Hallucis Longus muscle strength was 3/5, and left Achilles reflex was hypoactive. Lumbar spinal Magnetic Resonance Imaging revealed left L5-S1 facet hypertrophy. Lumbar radiculopathy due to lumbar facet hypertrophy is a well-known neurological condition. Radicular pain develops during the late postoperative period following lumbar disc hernia operations that are often related to recurrent disc herniation or to formation of post-operative scar tissue. In addition, it can be speculated that unilateral facet hypertrophy, which may develop after a disc hernia operation, might also be one of the causes of radiculopathy.

  20. Surgical Strategies for Spondylodiscitis due to Lumbar Disc Surgery.

    Science.gov (United States)

    Kucuk, Ahmet; Karademir, Mustafa; Tumturk, Abdulfettah; Ulutabanca, Halil; Ercal, Baris Derya; Senol, Serkan; Menku, Ahmet

    2017-01-01

    Despite different surgical treatment protocols at different centers for spondylodiscitis due to lumbar surgery, there is no consensus on its surgical indications. In this study, we aimed to clarify the steps to be followed in the management and treatment of postoperative spondylodiscitis. The data of 20 cases with postoperative spondylodiscitis were evaluated. C-reactive protein (CRP) was used for diagnosis and follow-up. According to culture results of the infected material obtained from the operated cases, appropriate antibiotic treatment was initiated. In non-operated cases, parenteral empirical antibiotic treatment was implemented. Surgical treatment was planned for cases with clinical and radiological instability, abscess on imaging and those who were nonrespondent to empirical antibiotic treatment. For the cases that clinically recovered and had normal CRP levels, oral antibiotic treatment was continued after parenteral antibiotic treatment. Of the cases; 13 were male (65%) and 7 were femals (35%). The mean age was 56.3 years (32-74). The most prevalent complaints in referral were waist and leg pain. Except one, all cases had increased CRP levels. All patients had spondylodiscitis on magnetic resonance imaging. Seven had radiological and clinical instability and 3 had epidural abscess. The most commonly growing microorganism in culture was Staphylococcus aureus. Surgical treatment was applied to seven cases and medical treatment to 13 cases. In cases with waist pain in the postoperative period, the first potential diagnosis to be considered is spondylodiscitis. Surgical treatment should be implemented for cases resistant to empirical antibiotic treatment, with abscess on imaging, or with lumbar instability.

  1. Is the spiral morphology of the Elias 2-27 circumstellar disc due to gravitational instability?

    Science.gov (United States)

    Hall, Cassandra; Rice, Ken; Dipierro, Giovanni; Forgan, Duncan; Harries, Tim; Alexander, Richard

    2018-02-01

    A recent ALMA observation of the Elias 2-27 system revealed a two-armed structure extending out to ˜300 au in radius. The protostellar disc surrounding the central star is unusually massive, raising the possibility that the system is gravitationally unstable. Recent work has shown that the observed morphology of the system can be explained by disc self-gravity, so we examine the physical properties of the disc necessary to detect self-gravitating spiral waves. Using three-dimensional Smoothed Particle Hydrodynamics, coupled with radiative transfer and synthetic ALMA imaging, we find that observable spiral structure can only be explained by self-gravity if the disc has a low opacity (and therefore efficient cooling), and is minimally supported by external irradiation. This corresponds to a very narrow region of parameter space, suggesting that, although it is possible for the spiral structure to be due to disc self-gravity, other explanations, such as an external perturbation, may be preferred.

  2. Percutaneous endoscopic cervical discectomy for discogenic cervical headache due to soft disc herniation

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, Y.; Lee, S.H.; Shin, S.W. [Wooridul Spine Hospital, Department of Neurosurgery, Kangnam-gu (Korea); Chung, S.E.; Park, H.S. [Wooridul Spine Hospital, Department of Radiology, Kangnam-gu (Korea)

    2005-12-01

    A discogenic cervical headache is a subtype of cervicogenic headache (CEH) that arises from a degenerative cervical disc abnormality. The purpose of this study was to evaluate the clinical outcome of percutaneous endoscopic cervical discectomy (PECD) for patients with chronic cervical headache due to soft cervical disc herniation. Seventeen patients underwent PECD for intractable headache. The inclusion criteria were soft disc herniation without segmental instability, proven by both local anesthesia and provocative discography for headache unresponsive to conservative treatment. The mean follow-up period was 37.6 months. Fifteen of the 17 patients (88.2%) showed successful outcomes based on the Macnab criteria. Pain scores on a visual analog scale (VAS) improved from a preoperative mean of 8.35{+-}0.79 to 2.12{+-}1.17, postoperatively (P<0.01). The mean disc height decreased from 6.81{+-}1.08 to 5.98{+-}1.07 mm (P<0.01). There was no newly developed segmental instability or spontaneous fusion on follow-up radiography. In conclusion, PECD appears to be effective for chronic severe discogenic cervical headache under strict inclusion criteria. (orig.)

  3. Percutaneous endoscopic cervical discectomy for discogenic cervical headache due to soft disc herniation

    International Nuclear Information System (INIS)

    Ahn, Y.; Lee, S.H.; Shin, S.W.; Chung, S.E.; Park, H.S.

    2005-01-01

    A discogenic cervical headache is a subtype of cervicogenic headache (CEH) that arises from a degenerative cervical disc abnormality. The purpose of this study was to evaluate the clinical outcome of percutaneous endoscopic cervical discectomy (PECD) for patients with chronic cervical headache due to soft cervical disc herniation. Seventeen patients underwent PECD for intractable headache. The inclusion criteria were soft disc herniation without segmental instability, proven by both local anesthesia and provocative discography for headache unresponsive to conservative treatment. The mean follow-up period was 37.6 months. Fifteen of the 17 patients (88.2%) showed successful outcomes based on the Macnab criteria. Pain scores on a visual analog scale (VAS) improved from a preoperative mean of 8.35±0.79 to 2.12±1.17, postoperatively (P<0.01). The mean disc height decreased from 6.81±1.08 to 5.98±1.07 mm (P<0.01). There was no newly developed segmental instability or spontaneous fusion on follow-up radiography. In conclusion, PECD appears to be effective for chronic severe discogenic cervical headache under strict inclusion criteria. (orig.)

  4. Enhanced activity of massive black holes by stellar capture assisted by a self-gravitating accretion disc

    Czech Academy of Sciences Publication Activity Database

    Karas, Vladimír; Šubr, L.

    2007-01-01

    Roč. 470, č. 1 (2007), s. 11-19 ISSN 0004-6361 R&D Projects: GA ČR GA205/07/0052; GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : black hole physics * accretion Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.259, year: 2007

  5. Hot-spot model for accretion disc variability as random process II. Mathematics of the power-spectrum break frequency

    Czech Academy of Sciences Publication Activity Database

    Pecháček, Tomáš; Goosmann, R. W.; Karas, Vladimír; Czerny, B.; Dovčiak, Michal

    2013-01-01

    Roč. 556, August (2013), A77/1-A77/12 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GC13-00070J Institutional support: RVO:67985815 Keywords : accretion * black holes Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.479, year: 2013

  6. Planet population synthesis driven by pebble accretion in cluster environments

    Science.gov (United States)

    Ndugu, N.; Bitsch, B.; Jurua, E.

    2018-02-01

    The evolution of protoplanetary discs embedded in stellar clusters depends on the age and the stellar density in which they are embedded. Stellar clusters of young age and high stellar surface density destroy protoplanetary discs by external photoevaporation and stellar encounters. Here, we consider the effect of background heating from newly formed stellar clusters on the structure of protoplanetary discs and how it affects the formation of planets in these discs. Our planet formation model is built on the core accretion scenario, where we take the reduction of the core growth time-scale due to pebble accretion into account. We synthesize planet populations that we compare to observations obtained by radial velocity measurements. The giant planets in our simulations migrate over large distances due to the fast type-II migration regime induced by a high disc viscosity (α = 5.4 × 10-3). Cold Jupiters (rp > 1 au) originate preferably from the outer disc, due to the large-scale planetary migration, while hot Jupiters (rp meaning that more gas giants are formed at larger metallicity. However, our synthetic population of isolated stars host a significant amount of giant planets even at low metallicity, in contradiction to observations where giant planets are preferably found around high metallicity stars, indicating that pebble accretion is very efficient in the standard pebble accretion framework. On the other hand, discs around stars embedded in cluster environments hardly form any giant planets at low metallicity in agreement with observations, where these changes originate from the increased temperature in the outer parts of the disc, which prolongs the core accretion time-scale of the planet. We therefore conclude that the outer disc structure and the planet's formation location determines the giant planet occurrence rate and the formation efficiency of cold and hot Jupiters.

  7. Constraints on the evolution of black hole spin due to magnetohydrodynamic accretion

    International Nuclear Information System (INIS)

    Takahashi, Masaaki; Tomimatsu, Akira

    2008-01-01

    Stationary and axisymmetric ideal magnetohydrodynamic (MHD) accretion onto a black hole is studied analytically. The accreting plasma ejected from a plasma source with low velocity must be superfast magnetosonic before passing through the event horizon. We work out and apply a trans-fast magnetosonic solution without detailed analysis of the regularity conditions at the magnetosonic point, by introducing the bending angle β of the magnetic field line, which is the ratio of the toroidal and poloidal components of the magnetic field. To accrete onto a black hole, the trans-magnetosonic solution has some restrictions on β, which are related to the field-aligned parameters of the MHD flows. One of the restrictions gives the boundary condition at the event horizon for the inclination of a magnetic field line. We find that this inclination is related to the energy and angular momentum transport to the black hole. Then, we discuss the spin-up/down process of a rotating black hole by cold MHD inflows in a secular evolution time scale. There are two asymptotic states for the spin evolution. One is that the angular velocity of the black hole approaches to that of the magnetic field line, and the other is that the spin-up effect by the positive angular momentum influx and the spin-down effect by the energy influx (as the mass-energy influx) are canceled. We also show that the MHD inflows prevents the evolution to the maximally rotating black hole.

  8. Evidence for Precession due to Supercritical Accretion in Ultraluminous X-Ray Sources

    Science.gov (United States)

    Weng, Shan-Shan; Feng, Hua

    2018-02-01

    Most ultraluminous X-ray sources (ULXs) are thought to be supercritical accreting compact objects, where massive outflows are inevitable. Using the long-term monitoring data with the Swift X-ray Telescope, we identified a common feature in bright, hard ULXs: they display a quasi-periodic modulation in their hard X-ray band but not in their soft band. As a result, some sources show a bimodal distribution on the hardness intensity map. We argue that these model-independent results can be well interpreted in a picture that involves supercritical accretion with precession, where the hard X-ray emission from the central funnel is more or less beamed, while the soft X-rays may arise from the photosphere of the massive outflow and be nearly isotropic. It implies that precession may be ubiquitous in supercritical systems, such as the Galactic microquasar SS 433. How the hard X-rays are modulated can be used to constrain the angular distribution of the hard X-ray emission and the geometry of the accretion flow. We also find that two ULX pulsars (NGC 5907 ULX-1 and NGC 7793 P13) show similar behaviors but no bimodal distribution, which may imply that they have a different beaming shape or mechanism.

  9. Partial dust obscuration in active galactic nuclei as a cause of broad-line profile and lag variability, and apparent accretion disc inhomogeneities

    Science.gov (United States)

    Gaskell, C. Martin; Harrington, Peter Z.

    2018-04-01

    The profiles of the broad emission lines of active galactic nuclei (AGNs) and the time delays in their response to changes in the ionizing continuum ("lags") give information about the structure and kinematics of the inner regions of AGNs. Line profiles are also our main way of estimating the masses of the supermassive black holes (SMBHs). However, the profiles often show ill-understood, asymmetric structure and velocity-dependent lags vary with time. Here we show that partial obscuration of the broad-line region (BLR) by outflowing, compact, dusty clumps produces asymmetries and velocity-dependent lags similar to those observed. Our model explains previously inexplicable changes in the ratios of the hydrogen lines with time and velocity, the lack of correlation of changes in line profiles with variability of the central engine, the velocity dependence of lags, and the change of lags with time. We propose that changes on timescales longer than the light-crossing time do not come from dynamical changes in the BLR, but are a natural result of the effect of outflowing dusty clumps driven by radiation pressure acting on the dust. The motion of these clumps offers an explanation of long-term changes in polarization. The effects of the dust complicate the study of the structure and kinematics of the BLR and the search for sub-parsec SMBH binaries. Partial obscuration of the accretion disc can also provide the local fluctuations in luminosity that can explain sizes deduced from microlensing.

  10. Compact binary merger and kilonova: outflows from remnant disc

    Science.gov (United States)

    Yi, Tuan; Gu, Wei-Min; Liu, Tong; Kumar, Rajiv; Mu, Hui-Jun; Song, Cui-Ying

    2018-05-01

    Outflows launched from a remnant disc of compact binary merger may have essential contribution to the kilonova emission. Numerical calculations are conducted in this work to study the structure of accretion flows and outflows. By the incorporation of limited-energy advection in the hyper-accretion discs, outflows occur naturally from accretion flows due to imbalance between the viscous heating and the sum of the advective and radiative cooling. Following this spirit, we revisit the properties of the merger outflow ejecta. Our results show that around 10-3 ˜ 10-1 M⊙ of the disc mass can be launched as powerful outflows. The amount of unbound mass varies with the disc mass and the viscosity. The outflow-contributed peak luminosity is around 1040 ˜ 1041 erg s-1. Such a scenario can account for the observed kilonovae associated with short gamma-ray bursts, including the recent event AT2017gfo (GW170817).

  11. Multiwavelength temporal and spectral variability of the blazar OJ 287 during and after the 2015 December flare: a major accretion disc contribution

    Science.gov (United States)

    Kushwaha, Pankaj; Gupta, Alok C.; Wiita, Paul J.; Gaur, Haritma; de Gouveia Dal Pino, E. M.; Bhagwan, Jai; Kurtanidze, O. M.; Larionov, V. M.; Damljanovic, G.; Uemura, M.; Semkov, E.; Strigachev, A.; Bachev, R.; Vince, O.; Gu, Minfeng; Zhang, Z.; Abe, T.; Agarwal, A.; Borman, G. A.; Fan, J. H.; Grishina, T. S.; Hirochi, J.; Itoh, R.; Kawabata, M.; Kopatskaya, E. N.; Kurtanidze, S. O.; Larionova, E. G.; Larionova, L. V.; Mishra, A.; Morozova, D. A.; Nakaoka, T.; Nikolashvili, M. G.; Savchenko, S. S.; Troitskaya, Yu. V.; Troitsky, I. S.; Vasilyev, A. A.

    2018-01-01

    We present a multiwavelength spectral and temporal analysis of the blazar OJ 287 during its recent activity between 2015 December and 2016 May, showing strong variability in the near-infrared (NIR) to X-ray energies with detection at γ-ray energies as well. Most of the optical flux variations exhibit strong changes in polarization angle and degree. All the interband time lags are consistent with simultaneous emissions. Interestingly, on days with excellent data coverage in the NIR-UV bands, the spectral energy distributions (SEDs) show signatures of bumps in the visible-UV bands, never seen before in this source. The optical bump can be explained as accretion-disc emission associated with the primary black hole of mass ∼ 1.8 × 1010 M⊙ while the little bump feature in the optical-UV appears consistent with line emission. Further, the broad-band SEDs extracted during the first flare and during a quiescent period during this span show very different γ-ray spectra compared to previously observed flare or quiescent spectra. The probable thermal bump in the visible seems to have been clearly present since 2013 May, as found by examining all available NIR-optical observations, and favours the binary supermassive black hole model. The simultaneous multiwavelength variability and relatively weak γ-ray emission that shows a shift in the SED peak is consistent with γ-ray emission originating from inverse Compton scattering of photons from the line emission that apparently contributes to the little blue bump.

  12. Revealing general relativity effects from accretion events near a supermassive black hole

    Science.gov (United States)

    Karas, Vladimír; Dovčiak, Michal; Eckart, Andreas; Kunneriath, Devaky; Zamaninasab, Mohammad

    2014-12-01

    Accretion onto black holes often proceeds via an accretion disc or a temporary disclike pattern. Variability features, observed in the light curves of such objects, and theoretical models of accretion flows suggest that inner accretion discs are inhomogeneous and clumpy. We discuss the general relativity effects acting on the radiation signal from the inner accretion flow. To this end we consider the radiation flux and polarization properties originating from a blob of gas near a rotating black hole. The predicted observed polarization at infinity is changed from its local value due to strong gravity and fast orbital motion. Different processes can produce the observed pattern: in the context of Sgr A* flares, the synchrotron mechanism and the inverse Compton upscattering appear to be the most likely mechanisms. The energy dependence of the changing degree and angle of polarization should allow us to discriminate between rotating (Kerr) and a non-rotating (Schwarzschild) black hole.

  13. Differentiation of patients with chronic lombosciatica due to disc hernia using gait analysis techniques.

    Science.gov (United States)

    Tacu, Cristina; Rezuş, Elena; Boiculese, L V; Stratulat, I S; Miu, Silvia Nicoleta

    2010-01-01

    Nowadays gait analysis represent a modern technique used as a useful tool in the assessment of patients with locomotors disease. To make a differentiation of patients with chronic sciatica due to disc hernia using gait analysis techniques. Study was prospective, with consecutive selection of subjects according to eligibility criteria, using a control group. The number of subjects was 47: 28 patients and 19 healthy subjects. The patients were characterized clinically, imagistically and biomechanically. The biomechanically evaluation was made with VICON MX optical motion capture system. Our data of interest were: temporo-spatial and kinematic parameters. These data were factorial analyzed with a principal component extraction technique, resulting 10 variables, which characterized the system variability in 94.67%. Next step was represented by a hierarchical cluster analysis for sub-group identification. We have differentiated two clusters. The two clusters were individualized regarding the temporo-spatial parameters (opposite foot contact, step width) as well as the kinematic parameters (maximum upward rotation in stance of pelvis, maximum adduction of the hip in stance, maximum abduction of the hip in swing, maximum plantar flexion angle in swing, total sagittal plane excursion of the ankle). The two clusters can be defined as following: cluster 1: reduced stance phase and mainly distal problems (of the ankle); cluster 2: normal stance phase duration, severely low step width and mainly proximal problems (pelvic belt).

  14. Longitudinal parallel compression suture to control postopartum hemorrhage due to placenta previa and accrete.

    Science.gov (United States)

    Li, Guang-Tai; Li, Xiao-Fan; Wu, Baoping; Li, Guangrui

    2016-04-01

    To assess the efficacy and safety of longitudinal parallel compression suture to control heavy postpartum hemorrhage (PPH) in patients with placenta previa/accreta. Fifteen women received a longitudinal parallel compression suture to stop life-threatening PPH due to placenta previa with or without accreta during cesarean section. The suture apposed the anterior and posterior walls of the lower uterine segment together using an absorbable thread A 70-mm round needle with a Number-1 absorbable thread was used. The point of needle entry was 1 cm above the upper margin of the cervix and 1 cm from the right lateral border of the lower segment of the anterior wall. The suture was threaded through the uterine cavity to the serosa of the posterior wall. Then, it was directed upward and threaded from the posterior to the anterior wall at ∼1-2 cm above the upper boundary of the lower uterine segment and 3-cm medial to the right margin of the uterus. Both ends of the suture were tied on the anterior aspect of uterus. The left side was sutured in the same way. The success rate of the procedure was 86.7% (13/15). Two of 15 cases were concurrently administered gauze packing and achieved satisfactory hemostasis. All patients resumed a normal menstrual flow, and no postoperative anatomical or physiological abnormalities related to the suture were observed. Three women achieved further pregnancies after the procedure. Longitudinal parallel compression suture is a safe, easy, effective, practical, and conservative surgical technique to stop intractable PPH from the lower uterine segment, particularly in women who have a cesarean scar and placenta previa/accreta. Copyright © 2016. Published by Elsevier B.V.

  15. Magnetic field structure in accretion columns on HMXB and effects on CRSF

    Directory of Open Access Journals (Sweden)

    Mukherjee Dipanjan

    2014-01-01

    Full Text Available In accreting neutron star binaries, matter is channelled by the magnetic fields from the accretion disc to the poles of neutron stars forming an accretion mound. We model such mounds by numerically solving the Grad-Shafranov equation for axisymmetric static MHD equilibria. From our solutions we infer local distortion of field lines due to the weight of accreted matter. Variation in mass loading at the accretion disc will alter the shape of the accretion mound which will also affect the local field distortion. From simulations of cyclotron resonance scattering features from HMXBs, we conclude that local field distortion will greatly affect the shape and nature of the CRSF. From phase resolved spectral analysis one can infer the local field structure and hence the nature of mass loading of field lines at the accretion disc. We also study the stability of such mounds by performing MHD simulations using the PLUTO MHD code. We find that pressure and gravity driven instabilities depend on the total mass accreted and the nature of mass loading of the field lines.

  16. Acute chest pain in a top soccer player due to thoracic disc herniation.

    Science.gov (United States)

    Baranto, Adad; Börjesson, Mats; Danielsson, Barbro; Hellström, Mikael; Swärd, Leif

    2009-05-01

    Case report. An unusual and previously not reported case of upper thoracic disc herniation combined with acute chest pain, is presented. Disc herniation in the thoracic spine is rare. There are only a few cases of thoracic disc herniation in top athletes presented in the literature. The clinical presentation of a thoracic disc herniation can vary widely depending on its location and morphologic characteristics. Clinically, the acute symptoms may be severe. A 24-year-old soccer player with acute left-sided chest pain that started in the middle of a soccer game has been followed clinically and with MRI examinations for 3 years. MRI of the thoracic spine showed a left-sided paramedial disc herniation at T2-T3 level and the right-sided paramedial disc herniation at T3-T4 level. The player was prescribed initial rest and subsequent physical rehabilitation. He had no further symptoms during rehabilitation to full training, and could resume play and remained symptom free for the rest of the season.The following season, the player experienced a similar sudden thoracic pain episode during training. This time the chest pain was right-sided. A new MRI of the thoracic spine showed unchanged findings. The initial rehabilitation was similar to the one used in the first episode. After 15 months with no symptoms during normal life the player was allowed to increase the intensity of training gradually and after 2 years the patient played soccer at elite level again. However, 3 years later the symptoms relapsed and the player ended his career after another rehabilitation period. In conclusion, it is important to consider thoracic disc herniation as acute chest pain in athletes and that the long-term prognosis of this entity is not always good.

  17. Chinese herbal medicine for chronic neck pain due to cervical degenerative disc disease.

    Science.gov (United States)

    Trinh, Kien; Cui, Xuejun; Wang, Yong-Jun

    2010-11-15

    Systematic review. To assess the efficacy of Chinese herbal medicines in treating chronic neck pain with radicular signs or symptoms. Chronic neck pain with radicular signs or symptoms is a common condition. Many patients use complementary and alternative medicine, including traditional Chinese medicine, to address their symptoms. We electronically searched CENTRAL, MEDLINE, EMBASE, CINAHL, and AMED (up to 2009), the Chinese Biomedical Database and related herbal medicine databases in Japan and South Korea (up to 2007). We also contacted content experts and hand searched a number of journals published in China.We included randomized controlled trials with adults with a clinical diagnosis of cervical degenerative disc disease, cervical radiculopathy, or myelopathy supported by appropriate radiologic findings. The interventions were Chinese herbal medicines. The primary outcome was pain relief, measured with a visual analogue scale, numerical scale, or other validated tool. All 4 included studies were in Chinese; 2 of which were unpublished. Effect sizes were not clinically relevant and there was low quality evidence for all outcomes due to study limitations and sparse data (single studies). Two trials (680 participants) found that Compound Qishe Tablets relieved pain better in the short-term than either placebo or Jingfukang; one trial (60 participants) found than an oral herbal formula of Huangqi relieved pain better than Mobicox or Methycobal, and another trial (360 participants) showed that a topical herbal medicine, Compound Extractum Nucis Vomicae, relieved pain better than Diclofenac Diethylamine Emulgel. There is low quality evidence that an oral herbal medication, Compound Qishe Tablet, reduced pain more than placebo or Jingfukang and a topical herbal medicine, Compound Extractum Nucis Vomicae, reduced pain more than Diclofenac Diethylamine Emulgel. Further research is very likely to change both the effect size and our confidence in the results.

  18. Posterior migration of lumbar disc herniation - imaging dilemma due to contrast contraindication: a case report

    Directory of Open Access Journals (Sweden)

    Fabrício Guimarães Gonçalves

    2012-06-01

    Full Text Available Disc herniation with posterior epidural migration is a rare and often symptomatic entity. Multiple are the natural barriers that prevent this pattern of migration. Enhanced magnetic resonance imaging is the diagnostic modality of choice in these cases. The diagnostic dilemma in this case was the contraindication to the use of contrast since the patient was known to have chronic renal failure.

  19. Physical examination for lumbar radiculopathy due to disc herniation in patients with low-back pain.

    NARCIS (Netherlands)

    Windt, D.A.W.M. van der; Simons, E.; Riphagen, I.I.; Ammendolia, C.; Verhangen, A.P.; Laslett, M.; Devillé, W.; Deyo, R.A.; Bouter, L.M.; Vet, H.C.W. de; Aertgeerts, B.

    2010-01-01

    Background: Low-back pain with leg pain (sciatica) may be caused by a herniated intervertebral disc exerting pressure on the nerve root. Most patients will respond to conservative treatment, but in carefully selected patients, surgical discectomy may provide faster relief of symptoms. Primary care

  20. Chemical enrichment of the planet-forming region as probed by accretion

    Science.gov (United States)

    Booth, Richard A.; Clarke, Cathie J.

    2018-01-01

    The chemical conditions in the planet-forming regions of protoplanetary discs remain difficult to observe directly. Gas accreting from the disc on to the star provides a way to measure the elemental abundances because even refractory species are in an atomic gaseous form. Here, we compare the abundance ratios derived from ultraviolet lines probing T Tauri accretion streams to simple models of disc evolution. Although the interpretation of line ratios in terms of abundances is highly uncertain, discs with large cavities in mm images tend to have lower Si emission. Since this can naturally be explained by the suppressed accretion of dust, this suggests that abundance variations are at least partially responsible for the variations seen in the line ratios. Our models of disc evolution due to grain growth, radial drift and the flux of volatile species carried as ices on grain surfaces give rise to a partial sorting of the atomic species based on the volatility of their dominant molecular carriers. This arises because volatiles are left behind at their snow lines while the grains continue to drift. We show that this reproduces the main features seen in the accretion line ratio data, such as carbon-to-nitrogen ratios which are a few times solar and the correlation between the Si to volatile ratio with mm flux. We highlight the fact that developing a more robust linkage between line ratios and abundance ratios and acquiring data for larger samples have the potential to cast considerable light on the chemical history of protoplanetary discs.

  1. On the diversity and statistical properties of protostellar discs

    Science.gov (United States)

    Bate, Matthew R.

    2018-04-01

    We present results from the first population synthesis study of protostellar discs. We analyse the evolution and properties of a large sample of protostellar discs formed in a radiation hydrodynamical simulation of star cluster formation. Due to the chaotic nature of the star formation process, we find an enormous diversity of young protostellar discs, including misaligned discs, and discs whose orientations vary with time. Star-disc interactions truncate discs and produce multiple systems. Discs may be destroyed in dynamical encounters and/or through ram-pressure stripping, but reform by later gas accretion. We quantify the distributions of disc mass and radii for protostellar ages up to ≈105 yr. For low-mass protostars, disc masses tend to increase with both age and protostellar mass. Disc radii range from of order 10 to a few hundred au, grow in size on time-scales ≲ 104 yr, and are smaller around lower mass protostars. The radial surface density profiles of isolated protostellar discs are flatter than the minimum mass solar nebula model, typically scaling as Σ ∝ r-1. Disc to protostar mass ratios rarely exceed two, with a typical range of Md/M* = 0.1-1 to ages ≲ 104 yr and decreasing thereafter. We quantify the relative orientation angles of circumstellar discs and the orbit of bound pairs of protostars, finding a preference for alignment that strengths with decreasing separation. We also investigate how the orientations of the outer parts of discs differ from the protostellar and inner disc spins for isolated protostars and pairs.

  2. Radiculopathy due to microfibrillar collagen hemostat mimicking recurrence of disc herniation

    Energy Technology Data Exchange (ETDEWEB)

    Doita, M.; Nishida, K.; Kurosaka, M. [Kobe University Graduate School of Medicine, Department of Orthopedic Surgery, Kobe (Japan)

    2006-12-15

    Microfibrillar collagen hemostat (Avitene) is an absorbable topical hemostatic agent prepared from purified bovine corium collagen. A 65-year-old woman presented with left buttock and lower extremity radicular pain. The patient underwent a disc excision in which Avitene was used to control venous bleeding from the epidural space. Leg pain decreased postoperatively, but she developed radicular pain when she started walking 3 days after the operation. Magnetic resonance imaging (MRI) performed post-operatively showed there was a mass lesion located between the dural sac and L5 nerve root. The lesion exhibited high signal intensity on T1-weighted images and higher signal intensity at the rim of the mass on T2-weighted images. A second operation performed 10 days later revealed that the nerve root was adherent to an extradural granulomatous mass associated with Avitene. Macroscopically, the resected mass was found to be composed mainly of microfibrillar collagen hemostat materials. Hemostat agents may produce a clinically symptomatic, radiologically apparent mass lesion. When considering a mass lesion arising after spine surgery, the differential diagnosis should include foreign body granuloma along with recurrent disc herniation and peridural scar formation. (orig.)

  3. Delayed High Output Heart Failure due to Arteriovenous Fistula Complicated with Herniated Disc Surgery.

    Science.gov (United States)

    Park, Taeshik; Park, Sang Ho; Arora, Alok

    2016-12-01

    A 36-year-old male presented with progressive exertional dyspnea over months. Physical examination showed jugular venous distension, lung crecipitations, femoral bruit and pitting pedal edema. Echocardiogram showed a dilated right ventricle with severe pulmonary hypertension and a non collapsing inferior vena cava (IVC). On right heart catheterization, IVC oxygen saturation was noted at 92% suggesting arterial mixing; a computed tomography of the abdomen showed a fistula between the right common iliac artery to the right common iliac vein at L4 level and a massive IVC; this was linked to trauma from a disectomy done 16 years ago at L4-L5 level. Endovascular sealing with a 16 × 60 mm bifurcated stent graft (S & G Biotech, Seoul, Korea) was performed which led to complete resolution of the patient's dyspnea. Iatrogenic vascular injury during lumbar disc surgery, although rare, can lead to high output cardiac failure developing over months to years.

  4. Cauda Equina Syndrome Due to Lumbar Disc Herniation: a Review of Literature

    Directory of Open Access Journals (Sweden)

    Kapetanakis Stylianos

    2017-12-01

    Full Text Available Cauda equina syndrome (CES is a rare neurologic condition that is caused by compression of the cauda equina. Cauda equina consists of spinal nerves L2-L5, S1-S5 and the coccygeal nerve. The compression of these nerve roots can be caused mainly by lumbar disc herniation (45% of all causes. The diagnosis consists of two critical points: a detailed history and physical examination and b MRI or CT. The gold standard of the treatment of this syndrome is the surgical approach in combination with the timing of onset of symptoms. The surgery as an emergency situation is recommended in the fi rst 48 hours of onset of symptoms. Any delay in diagnosis and treatment leads to a poor prognosis of CES.

  5. Cauda Equina Syndrome Due to Lumbar Disc Herniation: a Review of Literature.

    Science.gov (United States)

    Kapetanakis, Stylianos; Chaniotakis, Constantinos; Kazakos, Constantinos; Papathanasiou, Jannis V

    2017-12-20

    Cauda equina syndrome (CES) is a rare neurologic condition that is caused by compression of the cauda equina. Cauda equina consists of spinal nerves L2-L5, S1-S5 and the coccygeal nerve. The compression of these nerve roots can be caused mainly by lumbar disc herniation (45% of all causes). The diagnosis consists of two critical points: a) detailed history and physical examination and b) MRI or CT. The gold standard of the treatment of this syndrome is the surgical approach in combination with the timing of onset of symptoms. The surgery as an emergency situation is recommended in the fi rst 48 hours of onset of symptoms. Any delay in diagnosis and treatment leads to a poor prognosis of CES.

  6. Estimates of success in patients with sciatica due to lumbar disc herniation depend upon outcome measure.

    Science.gov (United States)

    Haugen, Anne Julsrud; Grøvle, Lars; Brox, Jens Ivar; Natvig, Bård; Keller, Anne; Soldal, Dag; Grotle, Margreth

    2011-10-01

    The objectives were to estimate the cut-off points for success on different sciatica outcome measures and to determine the success rate after an episode of sciatica by using these cut-offs. A 12-month multicenter observational study was conducted on 466 patients with sciatica and lumbar disc herniation. The cut-off values were estimated by ROC curve analyses using Completely recovered or Much better on a 7-point global change scale as external criterion for success. The cut-off values (references in brackets) at 12 months were leg pain VAS 17.5 (0-100), back pain VAS 22.5 (0-100), Sciatica Bothersomeness Index 6.5 (0-24), Maine-Seattle Back Questionnaire 4.5 (0-12), and the SF-36 subscales bodily pain 51.5, and physical functioning 81.7 (0-100, higher values indicate better health). In conclusion, the success rates at 12 months varied from 49 to 58% depending on the measure used. The proposed cut-offs may facilitate the comparison of success rates across studies.

  7. Oxygen-ozone therapy for herniated lumbar disc in patients with subacute partial motor weakness due to nerve root compression.

    Science.gov (United States)

    Dall'Olio, Massimo; Princiotta, Ciro; Cirillo, Luigi; Budai, Caterina; de Santis, Fabio; Bartolini, Stefano; Serchi, Elena; Leonardi, Marco

    2014-10-31

    Intradiscal oxygen-ozone (O2-O3) chemonucleolysis is a well-known effective treatment for pain caused by protruding disc disease and nerve root compression due to bulging or herniated disc. The most widely used therapeutic combination is intradiscal injection of an O2-O3 mixture (chemonucleolysis), followed by periradicular injection of O2-O3, steroid and local anaesthetic to enhance the anti-inflammatory and analgesic effect. The treatment is designed to resolve pain and is administered to patients without motor weakness, whereas patients with acute paralysis caused by nerve root compression undergo surgery 24-48h after the onset of neurological deficit. This paper reports on the efficacy of O2-O3 chemonucleolysis associated with anti-inflammatory foraminal injection in 13 patients with low back pain and cruralgia, low back pain and sciatica and subacute partial motor weakness caused by nerve root compression unresponsive to medical treatment. All patients were managed in conjunction with our colleagues in the Neurosurgery Unit of Bellaria Hospital and the IRCCS Institute of Neurological Sciences, Bologna. The outcomes obtained are promising: 100% patients had a resolution of motor weakness, while 84.6% had complete pain relief. Our results demonstrate that O2-O3 therapy can be considered a valid treatment option for this category of patients.

  8. Gas Accretion via Condensation and Fountains

    Science.gov (United States)

    Fraternali, Filippo

    For most of their lives, galaxies are surrounded by large and massive coronae of hot gas, which constitute vast reservoirs for gas accretion. This chapter describes a mechanism that allows star-forming disc galaxies to extract gas from their coronae. Stellar feedback powers a continuous circulation (galactic fountain) of gas from the disc into the halo, producing mixing between metal-rich disc material and metal-poor coronal gas. This mixing causes a dramatic reduction of the cooling time of the corona making it condense and accrete onto the disc. This fountain-driven accretion model makes clear predictions for the kinematics of the extraplanar cold/warm gas in disc galaxies, which are in good agreement with a number of independent observations. The amount of gas accretion predicted by the model is of the order of what is needed to sustain star formation. Accretion is expected to occur preferentially in the outer parts of discs and its efficiency drops for higher coronal temperatures. Thus galaxies are able to gather new gas as long as they do not become too massive nor fall into large halos and they maintain their star-forming gaseous discs.

  9. Dynamic processes during accretion into a black hole

    Directory of Open Access Journals (Sweden)

    G. S. Bisonvatyi-kogan

    2001-01-01

    Full Text Available Accretion disc theory was first developed as a theory with the local heat balance, where the whole energy produced by a viscous heating was emitted to the sides of the disc. One of the most important new invention of this theory was a phenomenological treatment of the turbulent viscosity, known as “alpha” prescription, when the (rϕ component of the stress tensor was approximated by (αP with a unknown constant α This prescription played the role in the accretion disc theory as well important as the mixing-length theory of convection for stellar evolution. Sources of turbulence in the accretion disc are discussed, including nonlinear hydrodynamic turbulence, convection and magnetic filed role. In parallel to the optically thick geometrically thin accretion disc models, a new branch of the optically thin accretion disc models was discovered, with a larger thickness for the same total luminosity. The choice between these solutions should be done of the base of stability analysis. The ideas underlying the necessity to include advection into the accretion disc theory are presented and first models with advection are reviewed. The present status of the solution for a low-luminous optically thin accretion disc model with advection is discussed and the limits for an advection dominated accretion flows (ADAF imposed by the presence of magnetic field are analyzed.

  10. Instability of warped discs

    Science.gov (United States)

    Doǧan, S.; Nixon, C. J.; King, A. R.; Pringle, J. E.

    2018-01-01

    Accretion discs are generally warped. If a warp in a disc is too large, the disc can `break' apart into two or more distinct planes, with only tenuous connections between them. Further if an initially planar disc is subject to a strong differential precession, then it can be torn apart into discrete annuli that precess effectively independently. In previous investigations, torque-balance formulae have been used to predict where and when the disc breaks into distinct parts. In this work, focusing on discs with Keplerian rotation and where the shearing motions driving the radial communication of the warp are damped locally by turbulence (the `diffusive' regime), we investigate the stability of warped discs to determine the precise criterion for an isolated warped disc to break. We find and solve the dispersion relation, which in general yields three roots. We provide a comprehensive analysis of this viscous-warp instability and the emergent growth rates and their dependence on disc parameters. The physics of the instability can be understood as a combination of (1) a term which would generally encapsulate the classical Lightman-Eardley instability in planar discs (given by ∂(νΣ)/∂Σ condition acting on the diffusion of the warp amplitude given in simplified form by ∂(ν2|ψ|)/∂|ψ| < 0. We discuss our findings in the context of discs with an imposed precession, and comment on the implications for different astrophysical systems.

  11. Serum cytokine levels in patients with chronic low back pain due to herniated disc: analytical cross-sectional study

    Directory of Open Access Journals (Sweden)

    Durval Campos Kraychete

    Full Text Available CONTEXT AND OBJECTIVE: The role of immune response and proinflammatory cytokines in the pathogenesis of chronic pain has been of growing interest. In order to evaluate whether there is any association between disc herniation and elevated cytokine levels, we measured cytokine levels in patients with chronic low back pain and in healthy subjects. DESIGN AND SETTING: Analytical cross-sectional study at the Pain Clinic of Universidade Federal da Bahia (UFBA. METHODS: Cytokine levels were measured using the enzyme-linked immunosorbent assay (ELISA technique on 23 patients with low back pain (G1 and on 10 healthy subjects (G2. RESULTS: The levels of tumor necrosis factor-alpha [TNF-alpha] (G1 = 5.6 ± 2.3 pg/ml; G2 = 1.6 ± 0.5 pg/ml; P = 0.01 and interleukin-6 [IL-6] (G1 = 4.1 ± 3.0 pg/ml; G2 = 0.9 ± 0.4 pg/ml; P = 0.01 were higher in G1. There were no statistically significant differences in relation to interleukin-1 [IL-1] (G1 = 0.5 ± 0.3 pg/ml; G2 = 0.5 ± 0.1 pg/ml; P = 1 or soluble tumor necrosis factor receptor [sTNF-R] (G1 = 572 pg/ml ± 36; G2 = 581 ± 50 pg/ml; P = 0.87. CONCLUSION: The patients with chronic low back pain due to disc herniation presented higher levels of TNF-alpha and IL-6, but not of IL-1 or sTNF-R.

  12. Standing shocks in magnetized dissipative accretion flow around ...

    Indian Academy of Sciences (India)

    We explore the global structure of the accretion flow around a Schwarzschild black hole where the accretion disc is threaded by toroidal magnetic fields. The accretion flow is optically thin and advection dominated. The synchrotron radiation is considered to be the active cooling mechanism in the flow. With this, we obtain ...

  13. Standing shocks in magnetized dissipative accretion flow around ...

    Indian Academy of Sciences (India)

    BIPLOB SARKAR

    2018-02-09

    Feb 9, 2018 ... Abstract. We explore the global structure of the accretion flow around a Schwarzschild black hole where the accretion disc is threaded by toroidal magnetic fields. The accretion flow is optically thin and advection dominated. The synchrotron radiation is considered to be the active cooling mechanism in the ...

  14. The profiles of Fe K α line from the inhomogeneous accretion flow

    Science.gov (United States)

    Yu, Xiao-Di; Ma, Ren-Yi; Li, Ya-Ping; Zhang, Hui; Fang, Tao-Tao

    2018-05-01

    The clumpy disc, or inhomogeneous accretion flow, has been proposed to explain the properties of accreting black hole systems. However, the observational evidence remains to be explored. In this work, we calculate the profiles of Fe K α lines emitted from the inhomogeneous accretion flow through the ray-tracing technique, in order to find possible observable signals of the clumps. Compared with the skewed double-peaked profile of the continuous standard accretion disc, the lines show a multipeak structure when the emissivity index is not very steep. The peaks and wings are affected by the position and size of the cold clumps. When the clump is small and is located in the innermost region, due to the significant gravitational redshift, the blue wing can overlap with the red wing of the outer cold disc/clump, forming a fake peak or greatly enhancing the red peak. Given high enough resolution, it is easier to constrain the clumps around the supermassive black holes than the clumps in stellar mass black holes due to the thermal Doppler effect.

  15. The Profiles of Fe Kα Line From the Inhomogeneous Accretion Flow

    Science.gov (United States)

    Yu, Xiao-Di; Ma, Ren-Yi; Li, Ya-Ping; Zhang, Hui; Fang, Tao-Tao

    2018-02-01

    The clumpy disc, or inhomogeneous accretion flow, has been proposed to explain the properties of accreting black hole systems. However, the observational evidences remain to be explored. In this work, we calculate the profiles of Fe Kα lines emitted from the inhomogeneous accretion flow through the ray-tracing technique, in order to find possible observable signals of the clumps. Compared with the skewed double-peaked profile of the continuous standard accretion disc, the lines show a multi-peak structure when the emissivity index is not very steep. The peaks and wings are affected by the position and size of the cold clumps. When the clump is small and is located in the innermost region, due to the significant gravitational redshift, the blue wing can overlap with the red wing of the outer cold disc/clump, forming a fake peak or greatly enhancing the red peak. Given high enough resolution, it is easier to constrain the clumps around the supermassive black holes than the clumps in stellar mass black holes due to the thermal Doppler effect.

  16. Source to Accretion Disk Tilt

    OpenAIRE

    Montgomery, M. M.; Martin, E. L.

    2010-01-01

    Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source to cause and maintain disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through...

  17. Dead discs, unstable discs and the stars they surround

    Directory of Open Access Journals (Sweden)

    D’Angelo Caroline

    2014-01-01

    Full Text Available Strong stellar magnetic fields significantly alter the behaviour of surrounding accretion discs. Recent work has demonstrated that at low accretion rates a large amount of mass can remain confined in the disc, contrary to the standard assumption that the magnetic field will expel the disc in an outflow (the “propeller regime”. These “dead discs” often become unstable, causing cycles of accretion onto the central star. Here I present the main predictions of this model, and argue that it provides a good explanation for the peculiar behaviour seen in several accreting sources with strong magnetic fields. I will focus in particular on three accreting millisecond X-ray pulsars: SAX J1808.4-3658, NGC 6440 X-2 and IGR J00291+5934. These sources all show low-frequency quasi-periodic oscillations consistent with a variable accretion rate, as well as unusual outburst patterns that suggest gas is confined in the inner disc regions during quiescence.

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

    Science.gov (United States)

    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. Physical examination for lumbar radiculopathy due to disc herniation in patients with low-back pain (Review)

    NARCIS (Netherlands)

    van der Windt, D.A.W.M.; Simons, E.; Riphagen, I.I.; Ammendolia, C.; Verhagen, A.P.; Laslett, M.; Devillé, W.; Deyo, R.A.; Bouter, L.M.; de Vet, H.C.W.; Aertgeerts, B.

    2011-01-01

    Background Low-back pain with leg pain (sciatica) may be caused by a herniated intervertebral disc exerting pressure on the nerve root. Most patients will respond to conservative treatment, but in carefully selected patients, surgical discectomy may provide faster relief of symptoms. Primary care

  20. Magnetohydrodynamics of accretion disks

    International Nuclear Information System (INIS)

    Torkelsson, U.

    1994-04-01

    The thesis consists of an introduction and summary, and five research papers. The introduction and summary provides the background in accretion disk physics and magnetohydrodynamics. The research papers describe numerical studies of magnetohydrodynamical processes in accretion disks. Paper 1 is a one-dimensional study of the effect of magnetic buoyancy on a flux tube in an accretion disk. The stabilizing influence of an accretion disk corona on the flux tube is demonstrated. Paper 2-4 present numerical simulations of mean-field dynamos in accretion disks. Paper 11 verifies the correctness of the numerical code by comparing linear models to previous work by other groups. The results are also extended to somewhat modified disk models. A transition from an oscillatory mode of negative parity for thick disks to a steady mode of even parity for thin disks is found. Preliminary results for nonlinear dynamos at very high dynamo numbers are also presented. Paper 3 describes the bifurcation behaviour of the nonlinear dynamos. For positive dynamo numbers it is found that the initial steady solution is replaced by an oscillatory solution of odd parity. For negative dynamo numbers the solution becomes chaotic at sufficiently high dynamo numbers. Paper 4 continues the studies of nonlinear dynamos, and it is demonstrated that a chaotic solution appears even for positive dynamo numbers, but that it returns to a steady solution of mixed parity at very high dynamo numbers. Paper 5 describes a first attempt at simulating the small-scale turbulence of an accretion disk in three dimensions. There is only find cases of decaying turbulence, but this is rather due to limitations of the simulations than that turbulence is really absent in accretion disks

  1. SMBH accretion and mergers: removing the symmetries

    International Nuclear Information System (INIS)

    King, Andrew; Nixon, Chris

    2013-01-01

    We review recent progress in studying accretion flows on to supermassive black holes (SMBH). Much of this removes earlier assumptions of symmetry and regularity, such as aligned and prograde disc rotation. This allows a much richer variety of effects, often because cancellation of angular momentum allows rapid infall. Potential applications include lower SMBH spins allowing faster mass growth and suppressing gravitational-wave reaction recoil in mergers, gas-assisted SMBH mergers, and near-dynamical accretion in galaxy centres. (paper)

  2. Clinical findings and electrodiagnostic testing in 108 consecutive cases of lumbosacral radiculopathy due to herniated disc.

    Science.gov (United States)

    Mondelli, M; Aretini, A; Arrigucci, U; Ginanneschi, F; Greco, G; Sicurelli, F

    2013-10-01

    This prospective study aim to examine whether clinical findings and electrodiagnostic testing (EDX) in patients with lumbosacral monoradiculopathy due to herniated disc (HD) differ as a function of root involvement level (L5 vs. S1) and HD zone (paramedian vs. intraforaminal). All patients with L4, L5 or S1 monoradiculopathy were prospectively enrolled at four electromyography (EMG) labs over a 2-year period. The diagnosis was based on a congruence between patient history and MRI evidence of HD. We compared the sensitivities of clinical findings and EDX with respect to both root involvement level and HD zone. Multivariate logistic regression was performed in order to verify the association between abnormal EMG, clinical, and neuroradiological findings. One hundred and eight patients (mean age 47.7 years, 55% men) were consecutively enrolled. Sensory loss in the painful dermatome was the most frequent finding at physical examination (56% of cases). EMG was abnormal in at least one muscle supplied by femoral and sciatic nerves in 45 cases (42%). Inclusion of paraspinal muscles increased sensitivity to only 49% and that of proximal muscles was useless. Motor and sensory neurography was seldom abnormal. The most frequent motor neurographic abnormalities were a delay of F-wave minimum latency and decrease in the compound muscle action potential amplitude from extensor digitorum brevis and abductor hallucis in L5 and S1 radiculopathies, respectively. Sensory neurography was usually normal, the amplitude of sensory nerve action potential was seldom reduced when HD injured dorsal root ganglion or postganglionic root fibres. Multivariate logistic regression analysis showed that EMG abnormalities could be predicted by myotomal muscular weakness, abnormal deep reflexes, and paraesthesiae. The only clinical and electrophysiological differences with respect to root involvement level concerned deep reflexes and motor neurography of deep peroneal and tibial nerves. Only some EDX

  3. Instability of warped discs

    Science.gov (United States)

    Doǧan, S.; Nixon, C. J.; King, A. R.; Pringle, J. E.

    2018-05-01

    Accretion discs are generally warped. If a warp in a disc is too large, the disc can `break' apart into two or more distinct planes, with only tenuous connections between them. Further, if an initially planar disc is subject to a strong differential precession, then it can be torn apart into discrete annuli that precess effectively independently. In previous investigations, torque-balance formulae have been used to predict where and when the disc breaks into distinct parts. In this work, focusing on discs with Keplerian rotation and where the shearing motions driving the radial communication of the warp are damped locally by turbulence (the `diffusive' regime), we investigate the stability of warped discs to determine the precise criterion for an isolated warped disc to break. We find and solve the dispersion relation, which, in general, yields three roots. We provide a comprehensive analysis of this viscous-warp instability and the emergent growth rates and their dependence on disc parameters. The physics of the instability can be understood as a combination of (1) a term that would generally encapsulate the classical Lightman-Eardley instability in planar discs (given by ∂(νΣ)/∂Σ < 0) but is here modified by the warp to include ∂(ν1|ψ|)/∂|ψ| < 0, and (2) a similar condition acting on the diffusion of the warp amplitude given in simplified form by ∂(ν2|ψ|)/∂|ψ| < 0. We discuss our findings in the context of discs with an imposed precession, and comment on the implications for different astrophysical systems.

  4. Cervical myelopathy due to single level disc herniation presenting as intramedullary mass lesion: What to do first?

    Directory of Open Access Journals (Sweden)

    Murat Sakir Eksi

    2015-01-01

    Full Text Available Cervical myelopathy (CM is mostly a degenerative process ending in myelopathic and/or radiculopathic syndromes. On T2-weighted magnetic resonance imaging (MRI, CM appears as a hyperintense area near the spondylotic spine. This high intensity signal depends on the impact of outer forces and their duration. It also determines the prognosis of the surgical candidate. A 40-year-old male patient admitted to our clinic with right upper extremity weakness and hypoesthesia that had started 2 months earlier. On neurological examination there was 2/5 motor weakness of right biceps brachii, and hypoesthesia over right C6 dermatome. Right upper extremity deep tendon reflexes were hypoactive, but lower ones were hyperactive. After clinical and radiological work-up, preliminary diagnosis was directed to a spinal intramedullary tumor. Total resection of the herniated cervical disc fragment and the mass lesion was managed. Pathology of the mass lesion was compatible with subacute infarct tissue and inflammatory response. Final diagnosis was CM under effect of cervical disc herniation. Contrast-enhanced spinal cord myelopathic lesions are very rare and resemble much more tumors and inflammatory processes. However, the principal treatment approach totally differs depending on pathology. When there are both a disc herniation and a high clinical suspicion; biopsy should be delayed. The most probable solution will be surgery for the disc disease with thorough preoperative scanning of vascular malformations; clinical and radiological close follow-up after surgery. Biopsy or surgical resection can be performed if patient deteriorates despite the primary surgery.

  5. Cervical myelopathy due to single level prolapsed disc and spondylosis: a comparative study on outcome between two groups

    Science.gov (United States)

    Ryu, Jong-Seon; Chae, Jong-Woo; Cho, Woo-Jin; Chang, Han; Kim, Sung-Soo

    2010-01-01

    This article describes a retrospective study on myelopathy, induced by monosegmental prolapsed disc and spondylosis. To assess pre- and postoperative clinical and radiological findings related to myelopathy, and factors influencing the outcome, 20 disc herniation (group A) and 11 spondylosis patients (group B) were studied. Average duration of myelopathy in groups A and B were 3 and 8.7 months, respectively. Anterior decompression and fusion were performed. Pre- and postoperative clinical and radiological findings and outcomes were assessed. Average preoperative disc heights were 85.9% of normal in group A and 72.7% in group B. Average anteroposterior canal diameter and Pavlov ratio at diseased level were 13.9 mm and 0.81 in group A, respectively, and 12.1 mm and 0.78 in group B. Five group A (25.0%) and four group B cases (36.4%) had radiculopathy. Cord compressions among 20 group A patients were median in seven and paramedian in 13. In the 11 group B patients, nine were median and two were paramedian. High signal intensity was observed in 19 group A and ten group B patients. Postoperative regression of T2-weighted high signal intensity in 14 group A (73.7%) and two group B patients (20.0%) was observed. Preoperative JOA scores in groups A and B were 10.3 and 12.8, respectively, which became 66.2 and 22.5 postoperatively. Neurological recovery was poorer in group B than in group A. Outcome was influenced by chronicity of myelopathy. PMID:20108087

  6. Standing shocks in magnetized dissipative accretion flow around ...

    Indian Academy of Sciences (India)

    BIPLOB SARKAR

    2018-02-09

    Feb 9, 2018 ... The consequences of large scale ordered magnetic fields in accretion disc theories are frequently inves- ... by the effect of differential rotation on the originally poloidal field lines linking layers rotating at ..... ter possesses high entropy content (Becker & Kazanas. 2001). For a dissipative accretion flow, the ...

  7. Study of magnetized accretion flow with cooling processes

    Indian Academy of Sciences (India)

    Kuldeep Singh

    2018-02-09

    Feb 9, 2018 ... 1973; Davidson & Ostriker 1973; Ghosh & Lamb. 1979; Lovelace et al. 1985, 1986; Camenzind 1990;. Paatz & Camenzind 1996; Ostriker & Shu 1995; Li. & Wilson 1999) which address some of the issues of magnetized accretion flow, for e.g., inner radius of accretion disc, transition zone and radiations from.

  8. ZOMG - II. Does the halo assembly history influence central galaxies and gas accretion?

    Science.gov (United States)

    Romano-Díaz, Emilio; Garaldi, Enrico; Borzyszkowski, Mikolaj; Porciani, Cristiano

    2017-08-01

    The growth rate and the internal dynamics of galaxy-sized dark-matter haloes depend on their location within the cosmic web. Haloes that sit at the nodes grow in mass till the present time and are dominated by radial orbits. Conversely, haloes embedded in prominent filaments do not change much in size and are dominated by tangential orbits. Using zoom hydrodynamical simulations including star formation and feedback, we study how gas accretes on to these different classes of objects, which, for simplicity, we dub 'accreting' and 'stalled' haloes. We find that all haloes get a fresh supply of newly accreted gas in their inner regions, although this slowly decreases with time, in particular for the stalled haloes. The inflow of new gas is always higher than (but comparable with) that of recycled material. Overall, the cold-gas fraction increases (decreases) with time for the accreting (stalled) haloes. In all cases, a stellar disc and a bulge form at the centre of the simulated haloes. The total stellar mass is in excellent agreement with expectations based on the abundance-matching technique. Many properties of the central galaxies do not seem to correlate with the large-scale environment in which the haloes reside. However, there are two notable exceptions that characterize stalled haloes with respect to their accreting counterparts: (I) The galaxy disc contains much older stellar populations. (II) Its vertical scaleheight is larger by a factor of 2 or more. This thickening is likely due to the heating of the long-lived discs by mergers and close flybys.

  9. SREM - WRS system module number 3348 for calculating the removal flux due to point, line or disc sources

    International Nuclear Information System (INIS)

    Grimstone, M.J.

    1978-06-01

    The WRS Modular Programming System has been developed as a means by which programmes may be more efficiently constructed, maintained and modified. In this system a module is a self-contained unit typically composed of one or more Fortran routines, and a programme is constructed from a number of such modules. This report describes one WRS module, the function of which is to calculate the uncollided flux and first-collision source from a disc source in a slab geometry system, a line source at the centre of a cylindrical system or a point source at the centre of a spherical system. The information given in this manual is of use both to the programmer wishing to incorporate the module in a programme, and to the user of such a programme. (author)

  10. The lamppost model: effects of photon trapping, the bottom lamp and disc truncation

    Science.gov (United States)

    Niedźwiecki, Andrzej; Zdziarski, Andrzej A.

    2018-04-01

    We study the lamppost model, in which the primary X-ray sources in accreting black-hole systems are located symmetrically on the rotation axis on both sides of the black hole surrounded by an accretion disc. We show the importance of the emission of the source on the opposite side to the observer. Due to gravitational light bending, its emission can increase the direct (i.e., not re-emitted by the disc) flux by as much as an order of magnitude. This happens for near to face-on observers when the disc is even moderately truncated. For truncated discs, we also consider effects of emission of the top source gravitationally bent around the black hole. We also present results for the attenuation of the observed radiation with respect to that emitted by the lamppost as functions of the lamppost height, black-hole spin and the degree of disc truncation. This attenuation, which is due to the time dilation, gravitational redshift and the loss of photons crossing the black-hole horizon, can be as severe as by several orders of magnitude for low lamppost heights. We also consider the contribution to the observed flux due to re-emission by optically-thick matter within the innermost stable circular orbit.

  11. Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

    Science.gov (United States)

    Ilee, J. D.; Oudmaijer, R. D.; Wheelwright, H. E.; Pomohaci, R.

    2018-04-01

    To date, there is no explanation as to why disc-tracing CO first overtone (or `bandhead') emission is not a ubiquitous feature in low- to medium-resolution spectra of massive young stellar objects, but instead is only detected toward approximately 25 per cent of their spectra. In this paper, we investigate the hypothesis that only certain mass accretion rates result in detectable bandhead emission in the near infrared spectra of MYSOs. Using an analytic disc model combined with an LTE model of the CO emission, we find that high accretion rates (≳ 10-4 M⊙yr-1) result in large dust sublimation radii, a larger contribution to the K-band continuum from hot dust at the dust sublimation radius, and therefore correspondingly lower CO emission with respect to the continuum. On the other hand, low accretion rates (≲ 10-6 M⊙yr-1) result in smaller dust sublimation radii, a correspondingly smaller emitting area of CO, and thus also lower CO emission with respect to the continuum. In general, moderate accretion rates produce the most prominent, and therefore detectable, CO first overtone emission. We compare our findings to a recent near-infrared spectroscopic survey of MYSOs, finding results consistent with our hypothesis. We conclude that the detection rate of CO bandhead emission in the spectra of MYSOs could be the result of MYSOs exhibiting a range of mass accretion rates, perhaps due to the variable accretion suggested by recent multi-epoch observations of these objects.

  12. Wind accretion: Theory and observations

    Science.gov (United States)

    Shakura, N. I.; Postnov, K. A.; Kochetkova, A. Yu.; Hjalmarsdotter, L.; Sidoli, L.; Paizis, A.

    2015-07-01

    A review of wind accretion in high-mass X-ray binaries is presented. We focus on different regimes of quasi-spherical accretion onto the neutron star (NS): the supersonic (Bondi) accretion, which takes place when the captured matter cools down rapidly and falls supersonically towards the NS magnetosphere, and subsonic (settling) accretion which occurs when plasma remains hot until it meets the magnetospheric boundary. These two regimes of accretion are separated by an X-ray luminosity of about 4 × 1036 erg s-1. In the subsonic case, which sets in at lower luminosities, a hot quasi-spherical shell must form around the magnetosphere, and the actual accretion rate onto NS is determined by the ability of the plasma to enter the magnetosphere due to Rayleigh-Taylor instability. In turn, two regimes of subsonic accretion are possible, depending on plasma cooling mechanism (Compton or radiative) near the magnetopshere. The transition from the high-luminosity with Compton cooling to the lowluminosity (Lx ≲ 3 × 1035 erg s-1) with radiative cooling can be responsible for the onset of the off states repeatedly observed in several low-luminosity slowly accreting pulsars, such as Vela X-1, GX 301-2, and 4U 1907+09. The triggering of the transitionmay be due to a switch in the X-ray beam pattern in response to a change in the optical depth in the accretion column with changing luminosity. We also show that in the settling accretion theory, bright X-ray flares (~1038-1040 erg) observed in supergiant fast X-ray transients (SFXT) can be produced by sporadic capture of magnetized stellar wind plasma. At sufficiently low accretion rates, magnetic reconnection can enhance the magnetospheric plasma entry rate, resulting in copious production of X-ray photons, strong Compton cooling and ultimately in unstable accretion of the entire shell. A bright flare develops on the free-fall time scale in the shell, and the typical energy released in an SFXT bright flare corresponds to the mass

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

    Science.gov (United States)

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

    2016-05-21

    The extreme luminosities of massive, hot OB stars drive strong stellar winds through line-scattering of the star's UV continuum radiation. For OB stars with an orbiting circumstellar disc, we explore here the effect of such line-scattering in driving an ablation of material from the disc's surface layers, with initial focus on the marginally optically thin decretion discs of classical Oe and Be stars. For this we apply a multidimensional radiation-hydrodynamics code that assumes simple optically thin ray tracing for the stellar continuum, but uses a multiray Sobolev treatment of the line transfer; this fully accounts for the efficient driving by non-radial rays, due to desaturation of line-absorption by velocity gradients associated with the Keplerian shear in the disc. Results show a dense, intermediate-speed surface ablation, consistent with the strong, blueshifted absorption of UV wind lines seen in Be shell stars that are observed from near the disc plane. A key overall result is that, after an initial adjustment to the introduction of the disc, the asymptotic disc destruction rate is typically just an order-unity factor times the stellar wind mass-loss rate. For optically thin Be discs, this leads to a disc destruction time of order months to years, consistent with observationally inferred disc decay times. The much stronger radiative forces of O stars reduce this time to order days, making it more difficult for decretion processes to sustain a disc in earlier spectral types, and so providing a natural explanation for the relative rarity of Oe stars in the Galaxy. Moreover, the decrease in line-driving at lower metallicity implies both a reduction in the winds that help spin-down stars from near-critical rotation, and a reduction in the ablation of any decretion disc; together these provide a natural explanation for the higher fraction of classical Be stars, as well as the presence of Oe stars, in the lower metallicity Magellanic Clouds. We conclude with a

  14. The prevalence of fibromyalgia among patients with cervical radiculopathy due to cervical disc herniation: a pilot study.

    Science.gov (United States)

    Demir, Saliha Eroglu; Aytekin, Ebru; Karacan, Ilhan; Aydin, Teoman; Kavadar, Gülis Durmusoglu

    2014-01-01

    Cervical disc herniation (CDH) is the most common cause of cervical radiculopathy and could overlap with fibromyalgia (FM). The primary aim of the present study was to investigate the prevalences of FM and widespread pain in patients with cervical radiculopathy diagnosed as CDH in a cross-sectional study. The secondary aim was to analyze the localization of tender points (TPs) and associated symptoms in these patients comparing patients with FM. Fifty-two patients with cervical radiculopathy who carried the diagnosis of CDH and 51 patients with FM included to the study. The patients were questioned for the distribution and the duration of pain and for a group of symptoms related to FM such as headache, fatigue with a two-point scale (0 "no", 1 "yes"). The diagnosis of CDH was made with patients' clinical evaluation and radiological findings with Magnetic Resonans Imaging Study. FM was diagnosed using the American College of Rheumatology criteria. Widespread pain was defined as all of the following parameters were present: pain in the left side of the body; pain in the right side of the body; pain above the waist; pain below the waist; axial skeletal pain; and duration of pain for more than 3 months. The number of TPs were counted by digital palpation. Six female patients (11.5%) with CDH fulfilled the ACR 1990 criteria for FM. Of the patients with CDH 71.8% of TPs were located around the neck and shoulder regions, while 58.7% of TPs of the patients with FM were located around these regions. There were statistically significant differences between the patients with CDH and the patients with FM in terms of the duration of widespread pain, the number of TPs and the localization of TPs (p< 0.05). The prevalences of FM and widespread pain in patients with CDH were found as 11.5% and 78.8% respectively.

  15. Accretion by the Galaxy

    Directory of Open Access Journals (Sweden)

    Binney J.

    2012-02-01

    Full Text Available Cosmology requires at least half of the baryons in the Universe to be in the intergalactic medium, much of which is believed to form hot coronae around galaxies. Star-forming galaxies must be accreting from their coronae. Hi observations of external galaxies show that they have Hi halos associated with star formation. These halos are naturally modelled as ensembles of clouds driven up by supernova bubbles. These models can fit the data successfully only if clouds exchange mass and momentum with the corona. As a cloud orbits, it is ablated and forms a turbulent wake where cold high-metallicity gas mixes with hot coronal gas causing the prompt cooling of the latter. As a consequence the total mass of Hi increases. This model has recently been used to model the Leiden-Argentina-Bonn survey of Galactic Hi. The values of the model’s parameters that are required to model NGC 891, NGC 2403 and our Galaxy show a remarkable degree of consistency, despite the very different natures of the two external galaxies and the dramatic difference in the nature of the data for our Galaxy and the external galaxies. The parameter values are also consistent with hydrodynamical simulations of the ablation of individual clouds. The model predicts that a galaxy that loses its cool-gas disc for instance through a major merger cannot reform it from its corona; it can return to steady star formation only if it can capture a large body of cool gas, for example by accreting a gas-rich dwarf. Thus the model explains how major mergers can make galaxies “red and dead.”

  16. Apparent quasar disc sizes in the "bird's nest" paradigm

    Science.gov (United States)

    Abolmasov, P.

    2017-04-01

    Context. Quasar microlensing effects make it possible to measure the accretion disc sizes around distant supermassive black holes that are still well beyond the spatial resolution of contemporary instrumentation. The sizes measured with this technique appear inconsistent with the standard accretion disc model. Not only are the measured accretion disc sizes larger, but their dependence on wavelength is in most cases completely different from the predictions of the standard model. Aims: We suggest that these discrepancies may arise not from non-standard accretion disc structure or systematic errors, as it was proposed before, but rather from scattering and reprocession of the radiation of the disc. In particular, the matter falling from the gaseous torus and presumably feeding the accretion disc may at certain distances become ionized and produce an extended halo that is free from colour gradients. Methods: A simple analytical model is proposed assuming that a geometrically thick translucent inflow acts as a scattering mirror changing the apparent spatial properties of the disc. This inflow may be also identified with the broad line region or its inner parts. Results: Such a model is able to explain the basic properties of the apparent disc sizes, primarily their large values and their shallow dependence on wavelength. The only condition required is to scatter a significant portion of the luminosity of the disc. This can easily be fulfilled if the scattering inflow has a large geometrical thickness and clumpy structure.

  17. Periodic self-lensing from accreting massive black hole binaries

    Science.gov (United States)

    D'Orazio, Daniel J.; Di Stefano, Rosanne

    2018-03-01

    Nearly 150 massive black hole binary (MBHB) candidates at sub-pc orbital separations have been reported in recent literature. Nevertheless, the definitive detection of even a single such object remains elusive. If at least one of the black holes is accreting, the light emitted from its accretion disc will be lensed by the other black hole for binary orbital inclinations near to the line of sight. This binary self-lensing could provide a unique signature of compact MBHB systems. We show that, for MBHBs with masses in the range 106-1010 M⊙ and with orbital periods less than ˜10 yr, strong lensing events should occur in one to 10s of per cent of MBHB systems that are monitored for an entire orbit. Lensing events will last from days for the less massive, shorter period MBHBs to a year for the most massive ˜10 year orbital period MBHBs. At small inclinations of the binary orbit to the line of sight, lensing must occur and will be accompanied by periodicity due to the relativistic Doppler boost. Flares at the same phase as the otherwise average flux of the Doppler modulation would be a smoking gun signature of self-lensing and can be used to constrain binary parameters. For MBHBs with separation ≳100 Schwarzschild radii, we show that finite-sized source effects could serve as a probe of MBH accretion disc structure. Finally, we stress that our lensing probability estimate implies that ˜10 of the known MBHB candidates identified through quasar periodicity should exhibit strong lensing flares.

  18. The effectiveness of transforaminal epidural steroid injection in patients with radicular low back pain due to lumbar disc herniation two years after treatment.

    Science.gov (United States)

    Taskaynatan, Mehmet Ali; Tezel, Kutay; Yavuz, Ferdi; Tan, Arif Kenan

    2015-01-01

    The aim of this retrospective study was to investigate the therapeutic effect of transforaminal epidural steroid injection in patients with chronic low back pain and radicular leg pain due to lumbar disc herniation. This study included 80 patients (32 female and 48 male; mean age: 45.8 years [range: 25-65 years]) that received fluoroscopically guided transforaminal epidural steroid injections for chronic radicular low back pain due to lumbar disc herniation. All of the patients had diagnostic MRI findings and did not respond to conservative treatment. All injections were performed by the same physician at the interventional pain unit of a tertiary hospital. The effectiveness of transforaminal epidural steroid injections was assessed via a standardized telephone questionnaire administered 2 years after the first injection. Mean duration of radicular low back pain was 24.50 ± 18.25 months. Most of the epidural injections were administered at the L5 and S1 levels. The most effective post-injection period was the first 5.11 ± 3.07 months. Mean duration of injection effect was 12.46 ± 7.24 months. The response rate to the epidural steroid injections was 72%. There was negative correlation between the duration of treatment effect and the duration of pre-treatment symptoms. Additionally, clinical improvement of radicular low back pain increased significantly as the duration of pre-treatment symptoms decreased. Based on the present findings, we think that transforaminal epidural steroid injections can be used as an alternative treatment for managing chronic radicular low back pain.

  19. Protoplanetary disc `isochrones' and the evolution of discs in the M˙-Md plane

    Science.gov (United States)

    Lodato, Giuseppe; Scardoni, Chiara E.; Manara, Carlo F.; Testi, Leonardo

    2017-12-01

    In this paper, we compare simple viscous diffusion models for the disc evolution with the results of recent surveys of the properties of young protoplanetary discs. We introduce the useful concept of 'disc isochrones' in the accretion rate-disc mass plane and explore a set of Monte Carlo realization of disc initial conditions. We find that such simple viscous models can provide a remarkable agreement with the available data in the Lupus star forming region, with the key requirement that the average viscous evolutionary time-scale of the discs is comparable to the cluster age. Our models produce naturally a correlation between mass accretion rate and disc mass that is shallower than linear, contrary to previous results and in agreement with observations. We also predict that a linear correlation, with a tighter scatter, should be found for more evolved disc populations. Finally, we find that such viscous models can reproduce the observations in the Lupus region only in the assumption that the efficiency of angular momentum transport is a growing function of radius, thus putting interesting constraints on the nature of the microscopic processes that lead to disc accretion.

  20. Gravitating discs around black holes

    International Nuclear Information System (INIS)

    Karas, V; Hure, J-M; Semerak, O

    2004-01-01

    Fluid discs and tori around black holes are discussed within different approaches and with the emphasis on the role of disc gravity. First reviewed are the prospects of investigating the gravitational field of a black hole-disc system using analytical solutions of stationary, axially symmetric Einstein equations. Then, more detailed considerations are focused to the middle and outer parts of extended disc-like configurations where relativistic effects are small and the Newtonian description is adequate. Within general relativity, only a static case has been analysed in detail. Results are often very inspiring. However, simplifying assumptions must be imposed: ad hoc profiles of the disc density are commonly assumed and the effects of frame-dragging are completely lacking. Astrophysical discs (e.g. accretion discs in active galactic nuclei) typically extend far beyond the relativistic domain and are fairly diluted. However, self-gravity is still essential for their structure and evolution, as well as for their radiation emission and the impact on the surrounding environment. For example, a nuclear star cluster in a galactic centre may bear various imprints of mutual star-disc interactions, which can be recognized in observational properties, such as the relation between the central mass and stellar velocity dispersion. (topical review)

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

    Science.gov (United States)

    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.

  2. The effects of a hot gaseous halo on disc thickening in galaxy minor mergers

    Science.gov (United States)

    Moster, Benjamin P.; Macciò, Andrea V.; Somerville, Rachel S.; Naab, Thorsten; Cox, T. J.

    2012-07-01

    We employ hydrodynamical simulations to study the effects of dissipational gas physics on the vertical heating and thickening of disc galaxies during minor mergers. For the first time we present a suite of simulations that includes a diffuse, rotating, cooling, hot gaseous halo, as predicted by cosmological hydrodynamical simulations as well as models of galaxy formation. We study the effect of this new gaseous component on the vertical structure of a Milky Way-like stellar disc during 1:10 and 1:5 mergers. For 1:10 mergers, we find no increased final thin disc scale height compared to the isolated simulation, leading to the conclusion that thin discs can be present even after a 1:10 merger if a reasonable amount of hot gas is present. The reason for this is the accretion of new cold gas, leading to the formation of a massive new thin stellar disc that dominates the surface brightness profile. In a previous study, in which we included only cold gas in the disc, we showed that the presence of cold gas decreased the thickening by a minor merger relative to the no-gas case. Here, we show that the evolution of the scale height in the presence of a cooling hot halo is dominated by the formation of the new stellar disc. In this scenario, the thick disc is the old stellar disc that has been thickened in a minor merger at z≳ 1, while the thin disc is the new stellar disc that reforms after this merger. When galactic winds are also considered, the final scale height is larger due to two effects. First, the winds reduce the star formation rate, leading to a less massive new stellar disc, such that the thickened old disc still dominates. Secondly, the winds exert a pressure force on the gas in the disc, leading to a shallower gas profile and thus to a thicker new stellar disc. In addition, we study the evolution of the scale height during a 1:5 merger and find that a thin disc can be present even after this merger, provided enough hot gas is available. The final scale

  3. A truly Newtonian softening length for disc simulations

    Czech Academy of Sciences Publication Activity Database

    Huré, J.-M.; Trova, Audrey

    2015-01-01

    Roč. 447, č. 2 (2015), s. 1866-1872 ISSN 0035-8711 Institutional support: RVO:67985815 Keywords : accretion discs * gravitation * numerical methods Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.952, year: 2015

  4. The multiplicity and anisotropy of galactic satellite accretion

    Science.gov (United States)

    Shao, Shi; Cautun, Marius; Frenk, Carlos S.; Grand, Robert J. J.; Gómez, Facundo A.; Marinacci, Federico; Simpson, Christine M.

    2018-02-01

    We study the incidence of group and filamentary dwarf galaxy accretion into Milky Way (MW) mass haloes using two types of hydrodynamical simulations: EAGLE, which resolves a large cosmological volume, and the AURIGA suite, which are very high resolution zoom-in simulations of individual MW-sized haloes. The present-day 11 most massive satellites are predominantly (75%) accreted in single events, 14% in pairs and 6% in triplets, with higher group multiplicities being unlikely. Group accretion becomes more common for fainter satellites, with 60% of the top 50 satellites accreted singly, 12% in pairs, and 28% in richer groups. A group similar in stellar mass to the Large Magellanic Cloud (LMC) would bring on average 15 members with stellar mass larger than 10^4{ M_\\odot}. Half of the top 11 satellites are accreted along the two richest filaments. The accretion of dwarf galaxies is highly anisotropic, taking place preferentially perpendicular to the halo minor axis, and, within this plane, preferentially along the halo major axis. The satellite entry points tend to be aligned with the present-day central galaxy disc and satellite plane, but to a lesser extent than with the halo shape. Dwarfs accreted in groups or along the richest filament have entry points that show an even larger degree of alignment with the host halo than the full satellite population. We also find that having most satellites accreted as a single group or along a single filament is unlikely to explain the MW disc of satellites.

  5. Accretion, primordial black holes and standard cosmology

    Indian Academy of Sciences (India)

    Primordial black holes evaporate due to Hawking radiation. We find that the evaporation times of primordial black holes increase when accretion of radiation is included. Thus, depending on accretion efficiency, more primordial black holes are existing today, which strengthens the conjecture that the primordial black holes ...

  6. Accretion, primordial black holes and standard cosmology

    Indian Academy of Sciences (India)

    Abstract. Primordial black holes evaporate due to Hawking radiation. We find that the evaporation times of primordial black holes increase when accretion of radiation is included. Thus, depending on accretion efficiency, more primordial black holes are existing today, which strengthens the con- jecture that the primordial ...

  7. Artificial Disc Replacement

    Science.gov (United States)

    ... Spondylolisthesis BLOG FIND A SPECIALIST Treatments Artificial Disc Replacement (ADR) Patient Education Committee Jamie Baisden The disc ... Disc An artificial disc (also called a disc replacement, disc prosthesis or spine arthroplasty device) is a ...

  8. The gravo-magneto disc instability with a viscous dead zone

    OpenAIRE

    Martin, Rebecca G.; Lubow, Stephen H.

    2013-01-01

    We consider the evolution of accretion discs that contain some turbulence within a disc dead zone, a region about the disc midplane of a disc that is not sufficiently ionised for the magneto-rotational instability (MRI) to drive turbulence. In particular, we determine whether additional sources of turbulence within a dead zone are capable of suppressing gravo-magneto (GM) disc outbursts that arise from a rapid transition from gravitationally produced to MRI produced turbulence. With viscous $...

  9. Gravitating discs around black holes

    Czech Academy of Sciences Publication Activity Database

    Karas, Vladimír; Huré, J.-M.; Semerák, O.

    2004-01-01

    Roč. 21, č. 7 (2004), R1-R5 ISSN 0264-9381 R&D Projects: GA ČR GA205/03/0902; GA AV ČR KSK1048102 Institutional research plan: CEZ:AV0Z1003909 Keywords : black holes * accretion discs * general relativity Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 2.941, year: 2004

  10. CT-guided steroid injection into disc herniation: a causative therapy for lower back pain due to disc herniation; CT-gesteuerte Prolaps-Steroidinjektion: Eine kausale Therapie des bandscheibenprolapsassoziierten Schmerzsyndroms

    Energy Technology Data Exchange (ETDEWEB)

    Vahlensieck, M.; Bruderhofer, A.F. [Radiologie Haydnhaus, Bonn (Germany); Waldecker, B.

    2005-01-01

    Purpose: to evaluate the therapeutic benefit of CT-guided steroid injection into disc herniations. Materials and methods: in 64 patients, 2.5 mg Dexamethasone was injected into a symptomatic disc herniation under CT-guidance. Conservative treatment 3 to 12 months before injection was unsuccessful. Classified as ''complete relief'', ''strong relief'', ''mild relief'' and ''no relief'' of pain, the change of discomfort and pain was registered at 14 days, 3 months and 6 months after injection while the conservative regimen continued. Results: at 14 days after injection, 36 patients (56%) showed complete relief, 5 strong relief (8%), 12 mild relief (19%) and 11 no relief (17%). At 6 months after injection, 25 patients showed complete relief (39%), 16 strong relief (25%), and 23 no relief (36%). One complicating spondylodiscitis was observed. Conclusion: CT-guided steroid injection into symptomatic disc herniation represents a therapeutic alternative with good therapeutic results. It can be recommended as an alterative to other minimal invasive therapeutic regimens. The disc material acts as reservoir for the drug with good long term depot effect. (orig.)

  11. Non-axisymmetric line-driven disc winds - I. Disc perturbations

    Science.gov (United States)

    Dyda, Sergei; Proga, Daniel

    2018-04-01

    We study mass outflows driven from accretion discs by radiation pressure due to spectral lines. To investigate non-axisymmetric effects, we use the ATHENA++ code and develop a new module to account for radiation pressure driving. In 2D, our new simulations are consistent with previous 2D axisymmetric solutions by Proga et al., who used the ZEUS 2D code. Specifically, we find that the disc winds are time dependent, characterized by a dense stream confined to ˜45° relative to the disc mid-plane and bounded on the polar side by a less dense, fast stream. In 3D, we introduce a vertical, ϕ-dependent, subsonic velocity perturbation in the disc mid-plane. The perturbation does not change the overall character of the solution but global outflow properties such as the mass, momentum, and kinetic energy fluxes are altered by up to 100 per cent. Non-axisymmetric density structures develop and persist mainly at the base of the wind. They are relatively small, and their densities can be a few times higher than the azimuthal average. The structure of the non-axisymmetric and axisymmetric solutions differ also in other ways. Perhaps most importantly from the observational point of view are the differences in the so-called clumping factors, that serve as a proxy for emissivity due to two body processes. In particular, the spatially averaged clumping factor over the entire fast stream, while it is of a comparable value in both solutions, it varies about 10 times faster in the non-axisymmetric case.

  12. Forming spectroscopic massive protobinaries by disc fragmentation

    Science.gov (United States)

    Meyer, D. M.-A.; Kuiper, R.; Kley, W.; Johnston, K. G.; Vorobyov, E.

    2018-01-01

    The surroundings of massive protostars constitute an accretion disc which has numerically been shown to be subject to fragmentation and responsible for luminous accretion-driven outbursts. Moreover, it is suspected to produce close binary companions which will later strongly influence the star's future evolution in the Hertzsprung-Russel diagram. We present three-dimensional gravitation-radiation-hydrodynamic numerical simulations of 100 M⊙ pre-stellar cores. We find that accretion discs of young massive stars violently fragment without preventing the (highly variable) accretion of gaseous clumps on to the protostars. While acquiring the characteristics of a nascent low-mass companion, some disc fragments migrate on to the central massive protostar with dynamical properties showing that its final Keplerian orbit is close enough to constitute a close massive protobinary system, having a young high- and a low-mass components. We conclude on the viability of the disc fragmentation channel for the formation of such short-period binaries, and that both processes - close massive binary formation and accretion bursts - may happen at the same time. FU-Orionis-type bursts, such as observed in the young high-mass star S255IR-NIRS3, may not only indicate ongoing disc fragmentation, but also be considered as a tracer for the formation of close massive binaries - progenitors of the subsequent massive spectroscopic binaries - once the high-mass component of the system will enter the main-sequence phase of its evolution. Finally, we investigate the Atacama Large (sub-)Millimeter Array observability of the disc fragments.

  13. MHD Simulations of Magnetized Stars in the Propeller Regime of Accretion

    Directory of Open Access Journals (Sweden)

    Lii Patrick

    2014-01-01

    Full Text Available Accreting magnetized stars may be in the propeller regime of disc accretion in which the angular velocity of the stellar magnetosphere exceeds that of the inner disc. In these systems, the stellar magnetosphere acts as a centrifugal barrier and inhibits matter accretion onto the rapidly rotating star. Instead, the matter accreting through the disc accumulates at the disc-magnetosphere interface where it picks up angular momentum and is ejected from the system as a wide-angled outflow which gradually collimates at larger distances from the star. If the ejection rate is lower than the accretion rate, the matter will accumulate at the boundary faster than it can be ejected; in this case, accretion onto the star proceeds through an episodic accretion instability in which the episodes of matter accumulation are followed by a brief episode of simultaneous ejection and accretion of matter onto the star. In addition to the matter dominated wind component, the propeller outflow also exhibits a well-collimated, magnetically-dominated Poynting jet which transports energy and angular momentum away from the star. The propeller mechanism may explain some of the weakly-collimated jets and winds observed around some T Tauri stars as well as the episodic variability present in their light curves. It may also explain some of the quasi-periodic variability observed in cataclysmic variables, millisecond pulsars and other magnetized stars.

  14. Shocks in the relativistic transonic accretion with low angular momentum

    Czech Academy of Sciences Publication Activity Database

    Suková, Petra; Charzynski, S.; Janiuk, A.

    2017-01-01

    Roč. 472, č. 4 (2017), s. 4327-4342 ISSN 0035-8711 R&D Projects: GA ČR(CZ) GJ17-06962Y Institutional support: RVO:67985815 Keywords : accretion discs * hydrodynamics * shock waves Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 4.961, year: 2016

  15. Study of magnetized accretion flow with cooling processes

    Indian Academy of Sciences (India)

    Kuldeep Singh

    2018-02-09

    —funnel flow. 1. Introduction. Neutron stars (NS) are very fascinating objects because they have strong magnetic and gravitation fields. Neu- tron stars accrete rotating matter from the companion, in the form of a disc, up to the ...

  16. Accretion on to Magnetic White Dwarfs

    Directory of Open Access Journals (Sweden)

    Wickramasinghe Dayal

    2014-01-01

    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 for blobby accretion in the generally lower field and disced IPs.

  17. The formation of planets by disc fragmentation

    Directory of Open Access Journals (Sweden)

    Stamatellos Dimitris

    2013-04-01

    Full Text Available I discuss the role that disc fragmentation plays in the formation of gas giant and terrestrial planets, and how this relates to the formation of brown dwarfs and low-mass stars, and ultimately to the process of star formation. Protostellar discs may fragment, if they are massive enough and can cool fast enough, but most of the objects that form by fragmentation are brown dwarfs. It may be possible that planets also form, if the mass growth of a proto-fragment is stopped (e.g. if this fragment is ejected from the disc, or suppressed and even reversed (e.g by tidal stripping. I will discuss if it is possible to distinguish whether a planet has formed by disc fragmentation or core accretion, and mention of a few examples of observed exoplanets that are suggestive of formation by disc fragmentation.

  18. Star-disc interaction in galactic nuclei: formation of a central stellar disc

    Science.gov (United States)

    Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

    2018-02-01

    We perform high resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc onto the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3% of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7% of the mass and 5% of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

  19. Structure of protoplanetary discs with magnetically driven winds

    Science.gov (United States)

    Khajenabi, Fazeleh; Shadmehri, Mohsen; Pessah, Martin E.; Martin, Rebecca G.

    2018-04-01

    We present a new set of analytical solutions to model the steady-state structure of a protoplanetary disc with a magnetically driven wind. Our model implements a parametrization of the stresses involved and the wind launching mechanism in terms of the plasma parameter at the disc midplane, as suggested by the results of recent, local magnetohydrodynamical simulations. When wind mass-loss is accounted for, we find that its rate significantly reduces the disc surface density, particularly in the inner disc region. We also find that models that include wind mass-loss lead to thinner dust layers. As an astrophysical application of our models, we address the case of HL Tau, whose disc exhibits a high accretion rate and efficient dust settling at its midplane. These two observational features are not easy to reconcile with conventional accretion disc theory, where the level of turbulence needed to explain the high accretion rate would prevent a thin dust layer. Our disc model that incorporates both mass-loss and angular momentum removal by a wind is able to account for HL Tau observational constraints concerning its high accretion rate and dust layer thinness.

  20. Polarimetric microlensing of circumstellar discs

    Science.gov (United States)

    Sajadian, Sedighe; Rahvar, Sohrab

    2015-12-01

    We study the benefits of polarimetry observations of microlensing events to detect and characterize circumstellar discs around the microlensed stars located at the Galactic bulge. These discs which are unresolvable from their host stars make a net polarization effect due to their projected elliptical shapes. Gravitational microlensing can magnify these signals and make them be resolved. The main aim of this work is to determine what extra information about these discs can be extracted from polarimetry observations of microlensing events in addition to those given by photometry ones. Hot discs which are closer to their host stars are more likely to be detected by microlensing, owing to more contributions in the total flux. By considering this kind of discs, we show that although the polarimetric efficiency for detecting discs is similar to the photometric observation, but polarimetry observations can help to constraint the disc geometrical parameters e.g. the disc inner radius and the lens trajectory with respect to the disc semimajor axis. On the other hand, the time-scale of polarimetric curves of these microlensing events generally increases while their photometric time-scale does not change. By performing a Monte Carlo simulation, we show that almost four optically thin discs around the Galactic bulge sources are detected (or even characterized) through photometry (or polarimetry) observations of high-magnification microlensing events during 10-yr monitoring of 150 million objects.

  1. The diverse lives of massive protoplanets in self-gravitating discs

    Science.gov (United States)

    Stamatellos, Dimitris; Inutsuka, Shu-ichiro

    2018-04-01

    Gas giant planets may form early-on during the evolution of protostellar discs, while these are relatively massive. We study how Jupiter-mass planet-seeds (termed protoplanets) evolve in massive, but gravitationally stable (Q≳1.5), discs using radiative hydrodynamic simulations. We find that the protoplanet initially migrates inwards rapidly, until it opens up a gap in the disc. Thereafter, it either continues to migrate inwards on a much longer timescale or starts migrating outwards. Outward migration occurs when the protoplanet resides within a gap with gravitationally unstable edges, as a high fraction of the accreted gas is high angular momentum gas from outside the protoplanet's orbit. The effect of radiative heating from the protoplanet is critical in determining the direction of the migration and the eccentricity of the protoplanet. Gap opening is facilitated by efficient cooling that may not be captured by the commonly used β-cooling approximation. The protoplanet initially accretes at a high rate (˜10-3MJ yr-1), and its accretion luminosity could be a few tenths of the host star's luminosity, making the protoplanet easily observable (albeit only for a short time). Due to the high gas accretion rate, the protoplanet generally grows above the deuterium-burning mass-limit. Protoplanet radiative feedback reduces its mass growth so that its final mass is near the brown dwarf-planet boundary. The fate of a young planet-seed is diverse and could vary from a gas giant planet on a circular orbit at a few AU from the central star to a brown dwarf on an eccentric, wide orbit.

  2. Relativistic jets from accreting black holes

    International Nuclear Information System (INIS)

    Coriat, Mickael

    2010-01-01

    Matter ejection processes, more commonly called jets, are among the most ubiquitous phenomena of the universe at ail scales of size and energy and are inseparable from accretion process. This intimate link, still poorly understood, is the main focus of this thesis. Through multi-wavelength observations of X-ray binary Systems hosting a black hole, I will try to bring new constraints on the physics of relativistic jets and the accretion - ejection coupling. We strive first to compare the simultaneous infrared, optical and X-ray emissions of the binary GX 339-4 over a period of five years. We study the nature of the central accretion flow, one of the least understood emission components of X-ray binaries, both in its geometry and in term of the physical processes that take place. This component is fundamental since it is could be the jets launching area or be highly connected to it. Then we focus on the infrared emission of the jets to investigate the physical conditions close to the jets base. We finally study the influence of irradiation of the outer accretion disc by the central X-ray source. Then, we present the results of a long-term radio and X-ray study of the micro-quasar H1743- 322. This System belongs to a population of accreting black holes that display, for a given X-ray luminosity, a radio emission fainter than expected. We make several assumptions about the physical origin of this phenomenon and show in particular that these sources could have a radiatively efficient central accretion flow. We finally explore the phases of return to the hard state of GX 339-4. We follow the re-emergence of the compact jets emission and try to bring new constraints on the physics of jet formation. (author) [fr

  3. On the high energy cut-off of accreting sources: Is general relativity relevant?

    Science.gov (United States)

    Tamborra, Francesco; Papadakis, Iossif; Dovčiak, Michal; Svoboda, Jiři

    2018-04-01

    The hard X-ray emission observed in accreting compact sources is believed to be produced by inverse Compton scattering of soft photons arising from the accretion disc by energetic electrons thermally distributed above the disc, the so-called X-ray corona. Many independent observations suggest that such coronae should be compact and located very close to the black hole. In this case, general relativistic (GR) effects should play an important role to the continuum X-ray emission from these sources, and, in particular, in the observed high energy cut-off, which is a measure of the intrinsic temperature of the corona. Our results show that the energy shift between the observed and intrinsic high energy cut-off due to GR effects can be as large as two to eight times, depending on the geometry and size of the corona as well as its inclination. We provide estimates of this energy shift in the case of a lamp-post and a flat, rotating corona, around a Kerr and a Schwartzschild black hole, for various inclinations, and coronal sizes. These values could be useful to correct the observed high energy cut-off and/or coronal temperatures, either in the case of individual or large sample of objects.

  4. Incompressible Wind Accretion

    Science.gov (United States)

    Tejeda, E.

    2018-04-01

    We present a simple, analytic model of an incompressible fluid accreting onto a moving gravitating object. This solution allows us to probe the highly subsonic regime of wind accretion. Moreover, it corresponds to the Newtonian limit of a previously known relativistic model of a stiff fluid accreting onto a black hole. Besides filling this blank in the literature, the new solution should be useful as a benchmark test for numerical hydrodynamics codes. Given its simplicity, it can also be used as an illustrative example in a gas dynamics course.

  5. Effects of ice accretion on the aerodynamics of bridge cables

    DEFF Research Database (Denmark)

    Demartino, C.; Koss, Holger; Georgakis, Christos T.

    2015-01-01

    Undesirable wind induced vibrations of bridge cables can occur when atmospheric conditions are such to generate ice accretion. This paper contains the results of an extensive investigation of the effects of ice accretion due to in-cloud icing, on the aerodynamic characteristics of bridge hangers...... and stay cables. The aim of this paper is twofold; first, it was investigated the ice accretion process and the final shape of the ice accreted; then the aerodynamics of the ice accreted bridge cables was characterized, and related to the ice shape. Different climatic conditions, i.e. combinations...... of temperature, wind speed and yaw angle of accretion, were reproduced in a climatic wind tunnel, giving rise to different types of accretion. These were chosen such to generate the most common natural ice formations expected to produce bridge cable vibrations. A description of the geometric characteristics...

  6. Cable Vibration due to Ice Accretions

    DEFF Research Database (Denmark)

    Gjelstrup, Henrik; Georgakis, Christos; Larsen, Allan

    investigation behind the causes of this relatively isolated hanger vibration event on the Great Belt East Bridge is presented. Furthermore a stability criterion for a 3DOF bluff body is proposed. One of the main assumptions of the investigation is that icy conditions may have contributed in some way to large...

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

    Czech Academy of Sciences Publication Activity Database

    Vierdayanti, K.; Sądowski, A.; Mineshige, L.S.; Bursa, Michal

    2013-01-01

    Roč. 436, č. 1 (2013), s. 71-81 ISSN 0035-8711 Institutional support: RVO:67985815 Keywords : accretion discs * black hole physics * GRS 1915+105 Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.226, year: 2013

  8. Rings and gaps in the disc around Elias 24 revealed by ALMA

    Science.gov (United States)

    Dipierro, G.; Ricci, L.; Pérez, L.; Lodato, G.; Alexander, R. D.; Laibe, G.; Andrews, S.; Carpenter, J. M.; Chandler, C. J.; Greaves, J. A.; Hall, C.; Henning, T.; Kwon, W.; Linz, H.; Mundy, L.; Sargent, A.; Tazzari, M.; Testi, L.; Wilner, D.

    2018-04-01

    We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle 2 observations of the 1.3-mm dust continuum emission of the protoplanetary disc surrounding the T Tauri star Elias 24 with an angular resolution of ˜0.2 arcsec (˜28 au). The dust continuum emission map reveals a dark ring at a radial distance of 0.47 arcsec (˜65 au) from the central star, surrounded by a bright ring at 0.58 arcsec (˜81 au). In the outer disc, the radial intensity profile shows two inflection points at 0.71 and 0.87 arcsec (˜99 and 121 au, respectively). We perform global three-dimensional smoothed particle hydrodynamic gas/dust simulations of discs hosting a migrating and accreting planet. Combining the dust density maps of small and large grains with three-dimensional radiative transfer calculations, we produce synthetic ALMA observations of a variety of disc models in order to reproduce the gap- and ring-like features observed in Elias 24. We find that the dust emission across the disc is consistent with the presence of an embedded planet with a mass of ˜0.7 MJ at an orbital radius of ˜ 60 au. Our model suggests that the two inflection points in the radial intensity profile are due to the inward radial motion of large dust grains from the outer disc. The surface brightness map of our disc model provides a reasonable match to the gap- and ring-like structures observed in Elias 24, with an average discrepancy of ˜5 per cent of the observed fluxes around the gap region.

  9. Ten years follow-up after surgery for a foveal detachment due to optic disc pit: a case report of outer retinal layer healing.

    Science.gov (United States)

    Giocanti-Aurégan, Audrey; Chbat, Elige A; Morel, Christophe G H; Morin, Bruno R; Conrath, John G; Devin, François C

    2017-12-04

    To report a case of complete progressive visual recovery and healing of outer retinal layers after vitrectomy for foveal detachment associated with optic disc pit. Optical coherence tomography (OCT) follow-up was performed on a 15-year-old boy with deep optic disc pit and foveal detachment, before and for 10 years after vitrectomy with gas. The foveal detachment was successfully reattached with complete reapplication of the retina. OCT scans showed a progressive long-term retinal healing with reappearance of the ellipsoid line and visual acuity improved from 20/100 before surgery to 20/25, 10 years after surgery. Photoreceptor regeneration after foveal detachment surgery has been already described only in zebrafish but never humans. However, we highlight with this case that in humans, a healing process of the outer retinal layers can occur with reappearance of the ellipsoid zone on OCT. This healing process may take several years and allow a complete functional restoration.

  10. Observing the On-going Formation of Planets and its Effects on Their Parent Discs

    Science.gov (United States)

    Willson, Matthew Alexander

    2017-06-01

    As the number of known exoplanetary systems has grown, it has become increasing apparent that our current understanding of planet formation is insufficient to explain the broad but distinct distributions of planets and planetary systems we observe. In particular, constructing a coherent model of planetary formation and migration within a circumstellar disc which is capable of producing both hot Jupiters or Solar System-like planetary system is high challenging. Resolved observations of where planets form and how they influence their parent discs provides essential information for tackling this important question. A promising technique for detecting close-in companions is Sparse Aperture Masking (SAM). The technique uses a mask to transform a single aperture telescope into a compact interferometric array capable of reliably detecting point sources at the diffraction limit or closer to a bright star with superior contrasts than extreme AO systems at the cost of smaller fields of view. Applying image reconstruction techniques to the interferometric information allows an observer to recover detailed structure in the circumstellar material. In this thesis I present work on the interpretation of SAM interferometry data on protoplanetary discs through the simulation of a number of scenarios expected to be commonly seen, and the application of this technique to a number of objects. Analysing data taken as part of a SAM survey of transitional and pre-transitional discs using the Keck-II/NIRC2 instrument, I detected three companion candidates within the discs of DM Tau, LkHα 330, and TW Hya, and resolved a gap in the disc around FP Tau as indicated by flux from the disc rim. The location of all three of the companions detected as part of the survey are positioned in interesting regions of their parent discs. The candidate, LkHα 330 b is a potentially cavity opening companion due to its close radial proximity to the inner rim of the outer disc. DM Tau b is located

  11. Demonstration of a magnetic Prandtl number disc instability from first principles

    OpenAIRE

    Potter, William J.; Balbus, Steven A.

    2017-01-01

    Understanding what determines the strength of MHD turbulence in accretion discs is a question of fundamental theoretical and observational importance. In this work we investigate whether the dependence of the turbulent accretion disc stress ($\\alpha$) on the magnetic Prandtl number (Pm) is sufficiently sensitive to induce thermal-viscous instability using 3D MHD simulations. We first investigate whether the $\\alpha$-Pm dependence, found by many previous authors, has a physical or numerical or...

  12. Gas accretion onto galaxies

    CERN Document Server

    Davé, Romeel

    2017-01-01

    This edited volume presents the current state of gas accretion studies from both observational and theoretical perspectives, and charts our progress towards answering the fundamental yet elusive question of how galaxies get their gas. Understanding how galaxies form and evolve has been a central focus in astronomy for over a century. These studies have accelerated in the new millennium, driven by two key advances: the establishment of a firm concordance cosmological model that provides the backbone on which galaxies form and grow, and the recognition that galaxies grow not in isolation but within a “cosmic ecosystem” that includes the vast reservoir of gas filling intergalactic space. This latter aspect in which galaxies continually exchange matter with the intergalactic medium via inflows and outflows has been dubbed the “baryon cycle”. The topic of this book is directly related to the baryon cycle, in particular its least well constrained aspect, namely gas accretion. Accretion is a rare area of ast...

  13. Relativistic, accreting disks

    International Nuclear Information System (INIS)

    Abramowicz, M.A; Jaroszynski, M.; Sikora, M.

    1978-01-01

    An analytic theory of the hydrodynamical structure of accreting disks (without self-gravitation but with pressure) orbiting around and axially symmetric, stationary, compact body (e.g. black hole) is presented. The inner edge of the marginally stable accreting disk (i.e. disk with constant angular momentum density) has a sharp cusp located on the equatorial plane between rsub(ms) and rsub(mb). The existence of the cusp is also typical for any angular momentum distribution. The physical importance of the cusp follows from the close analogy with the case of a close binary system (L 1 Lagrange point on the Roche lobe). The existence of the cusp is thus a crucial phenomenon in such problems as boundary condition for the viscous stresses, accretion rate etc. (orig.) [de

  14. Accreting CO material onto ONe white dwarfs towards accretion-induced collapse

    Science.gov (United States)

    Wu, Cheng-Yuan; Wang, Bo

    2018-03-01

    The final outcomes of accreting ONe white dwarfs (ONe WDs) have been studied for several decades, but there are still some issues that are not resolved. Recently, some studies suggested that the deflagration of oxygen would occur for accreting ONe WDs with Chandrasekhar masses. In this paper, we aim to investigate whether ONe WDs can experience accretion-induced collapse (AIC) or explosions when their masses approach the Chandrasekhar limit. Employing the stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA), we simulate the long-term evolution of ONe WDs with accreting CO material. The ONe WDs undergo weak multicycle carbon flashes during the mass-accretion process, leading to mass increase of the WDs. We found that different initial WD masses and mass-accretion rates influence the evolution of central density and temperature. However, the central temperature cannot reach the explosive oxygen ignition temperature due to neutrino cooling. This work implies that the final outcome of accreting ONe WDs is electron-capture induced collapse rather than thermonuclear explosion.

  15. Accretion flow diagnostics with X-ray spectral timing: the hard state of SWIFT J1753.5-0127

    NARCIS (Netherlands)

    Cassatella, P.; Uttley, P.; Maccarone, T.

    2012-01-01

    Recent XMM-Newton studies of X-ray variability in the hard states of black hole X-ray binaries (BHXRBs) indicate that the variability is generated in the ‘standard’ optically thick accretion disc that is responsible for the multi-colour blackbody emission. The variability originates in the disc as

  16. The slaved disc model for SS 433

    International Nuclear Information System (INIS)

    Whitmire, D.P.; Matese, J.J.

    1980-01-01

    A slaved disc model for SS 433 is investigated in which the beams originate normal to the surface of an accretion disc around a compact object in a binary system. The 13-day period in the 'stationary' system of lines is assumed to be associated with binary orbital motion and the 164-day periodicity in the moving line system is identified with disc precession. As in the slaved disc model for Her X-1, it is assumed that material is processed through the disc rapidly (relative to 164 days) so that the disc precesses at the same rate as the spin axis of the secondary which is driven by the gravitational torque applied by the compact object. If the secondary star does not underfill its critical lobe then the apparent absence of X-ray or optical eclipsing and beam interruption by the secondary places severe constraints on the model. It is shown that the viability of the basic model requires that the mass of the compact object be approximately > 10 times the mass of the secondary. Thus if the slaved disc model is applicable to SS 433 and if the mass of the secondary is approximately > 1 solar mass it follows that the compact object is a massive black hole. (author)

  17. Accretion by the Galaxy

    NARCIS (Netherlands)

    Binney, J.; Fraternali, F.; Reylé, C.; Robin, A.; Schultheis, M.

    Cosmology requires at least half of the baryons in the Universe to be in the intergalactic medium, much of which is believed to form hot coronae around galaxies. Star-forming galaxies must be accreting from their coronae. Hi observations of external galaxies show that they have Hi halos associated

  18. Late accretion to the terrestrial planets

    Science.gov (United States)

    Brasser, Ramon; Mojzsis, Stephen; Werner, Stephanie; Matsumura, Soko; Ida, Shigeru

    2017-10-01

    IntroductionIt is generally accepted that silicate-metal (`rocky') planet formation relies on coagulation from a mixture of sub-Mars sized planetary embryos and (smaller) planetesimals that dynamically emerge from the evolving circum-solar disc in the first few million years of our Solar System. Once the planets have, for the most part, assembled after a giant impact phase, they continue to be bombarded by a multitude of planetesimals left over from accretion. Here we place limits on the mass and evolution of these planetesimals based on constraints from the highly siderophile element (HSE) budget of the Moon. The terrestrial and lunar HSE budgets indicate that Earth’s and Moon’s additions through late accretion were 0.7 wt% and 0.02 wt% respectively. The disproportionate high accretion between the Earth and Moon could be explained by stochastic accretion of a few remaining Ceres-sized bodies that preferentially targeted the Earth.ResultsFrom a combination of N-body and Monte Carlo simulations of planet formation we conclude:1) matching the terrestrial to lunar HSE ratio requires that late accretion on Earth mostly consisted of a single lunar-size impactor striking the Earth before 4.45 Ga2) the flux of terrestrial impactors must have been low avoid wholesale melting of Earth's crust after 4.4 Ga[6], and to simultaneously match the number of observed lunar basins3) after the terrestrial planets have fully formed, the mass in remnant planetesimals was ~0.001 Earth mass, lower than most previous models suggest.4) Mars' HSE budget also requires a colossal impact with a Ceres-sized object before 4.43 Ga, whose visible remnant could be the hemispherical dichotomy.These conclusions lead to an Hadean eon which is more clement than assumed previously. In addition, our dynamically and geochemically self-consistent scenario requires that future N-body simulations of rocky planet formation either directly incorporate collisional grinding or rely on pebble accretion.

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

    Science.gov (United States)

    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), 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 reproduce the main features of cold gas observations in massive ellipticals, as the line fluxes and the filaments versus disk morphology. Such dichotomy is key for the long-term AGN feedback cycle. As gas cools, filamentary CCA develops and boosts AGN heating; the cold mode is thus reduced and the rotating disk remains the sole cold structure. Its consumption leaves the atmosphere in hot mode with suppressed accretion and feedback, reloading the cycle.

  20. X-ray pulsars: accretion flow deceleration

    International Nuclear Information System (INIS)

    Miller, G.S.

    1987-01-01

    X-ray pulsars are thought to be neutron stars that derive the energy for their x-ray emission by accreting material onto their magnetic polar caps. The accreting material and the x-ray pulsar atmospheres were idealized as fully ionized plasmas consisting only of electrons and protons. A high magnetic field (∼ 5 x 10 12 Gauss) permeates the atmospheric plasma, and causes the motion of atmospheric electrons perpendicular to the field to be quantized into discrete Landau levels. All atmospheric electrons initially lie in the Landau ground state, but in the author's calculations of Coulomb collisions between atmospheric electrons and accreting protons, he allows for processes that leave the electrons in the first excited Landau level. He also considers interactions between accreting protons and the collective modes of the atmospheric plasma. Division of the electromagnetic interaction of a fast proton with a magnetized plasma into single particle and collective effects is described in detail in Chapter 2. Deceleration of the accretion flow due to Coulomb collisions with atmospheric electrons and collective plasma effects was studied in a number of computer simulations. These simulations, along with a discussion of the physical state of the atmospheric plasma and its interactions with a past proton, are presented in Chapter 3. Details of the atmospheric model and a description of the results of the simulations are given in Chapter 4. Chapter 5 contains some brief concluding remarks, and some thoughts on future research

  1. Herniated lumbar disc

    OpenAIRE

    Jordon, Jo; Konstantinou, Kika; O'Dowd, John

    2009-01-01

    Herniated lumbar disc is a displacement of disc material (nucleus pulposus or annulus fibrosis) beyond the intervertebral disc space. The highest prevalence is among people aged 30-50 years, with a male to female ratio of 2:1.

  2. Herniated lumbar disc

    OpenAIRE

    Jordan, Jo; Konstantinou, Kika; O'Dowd, John

    2011-01-01

    Herniated lumbar disc is a displacement of disc material (nucleus pulposus or annulus fibrosis) beyond the intervertebral disc space. The highest prevalence is among people aged 30 to 50 years, with a male to female ratio of 2:1.

  3. Intradiscal O2O3: Rationale, Injection Technique, Short- and Long-term Outcomes for the Treatment of Low Back Pain Due to Disc Herniation.

    Science.gov (United States)

    Giurazza, Francesco; Guarnieri, Gianluigi; Murphy, Kieran J; Muto, Mario

    2017-05-01

    The management of low back pain should always start with a conservative approach; however, when it fails, intervention is required and at that moment the most appropriate choice remains unclear. Before invasive surgery, minimally invasive techniques can be adopted. In European trials and in a trans-Canadian clinical trial 03 ozone has been used successfully. In total over 50,000 patients have been treated safely. Ozone is a gas normally present in the atmosphere with potent oxidizing power; it has been used for percutaneous intradiscal injection combined with oxygen (O 2 O 3 ) at very low concentrations for 15 years in Europe. The main indication is back pain with or without radicular pain but without motor deficits, which is refractory to 4-6 weeks of conservative therapies. Its mechanism of action on the disc is mechanical (volume reduction by subtle dehydration of the nucleus pulposis) and antinflammatory. The intradiscal ozone injection is performed with a thin needle (18-22 gauge) image guided by computed tomography or angiofluoroscopy and is usually complimented by periganglionic injection of corticosteroids and anesthetics. This combination gives immediate pain relief and allows time for the ozone to act. It is a cost-effective procedure that presents a very low complication rate (0.1%). The radicular pain is resolved before the back pain does, as is seen with microdiscectomy. Peer-reviewed publications of large randomized trials, case series, and meta analysis from large samples of patients have demonstrated the procedure to be safe and effective in the short and the long terms, with benefits recognized up to 10 years after treatment. We aim to review the principles of action of O 2 O 3 and report the injection techniques, complications, and short- and long-term outcomes. Copyright © 2017 Canadian Association of Radiologists. Published by Elsevier Inc. All rights reserved.

  4. ISSLS Prize winner: Increased innervation and sensory nervous system plasticity in a mouse model of low back pain due to intervertebral disc degeneration.

    Science.gov (United States)

    Miyagi, Masayuki; Millecamps, Magali; Danco, Alexander T; Ohtori, Seiji; Takahashi, Kazuhisa; Stone, Laura S

    2014-08-01

    Immunohistochemical and behavioral study using the SPARC (secreted protein, acidic, rich in cysteine)-null mouse model of low back pain (LBP) associated with accelerated intervertebral disc (IVD) degeneration. To determine if behavioral signs of LBP in SPARC-null mice are accompanied by sensory nervous system plasticity. IVD pathology is a significant contributor to chronic LBP. In humans and rodents, decreased expression of SPARC is associated with IVD degeneration. We previously reported that SPARC-null mice exhibit age-dependent behavioral signs of chronic axial LBP and radiating leg pain. SPARC-null and age-matched control young, middle-aged, and old mice (1.5, 6, and 24 mo of age, respectively) were evaluated. Cutaneous hind paw sensitivity to cold, heat, and mechanical stimuli were evaluated as measures of radiating pain. The grip force and tail suspension assays were performed to evaluate axial LBP. Motor impairment was assessed using an accelerating rotarod. IVD innervation was identified by immunohistochemistry targeting the nerve fiber marker PGP9.5 and the sensory neuropeptide calcitonin gene-related peptide (CGRP). Sensory nervous system plasticity was evaluated by quantification of CGRP- and neuropeptide-Y-immunoreactivity (-ir) in dorsal root ganglia neurons and CGRP-ir, GFAP-ir (astrocyte marker), and Iba-1-ir (microglia marker) in the spinal cord. SPARC-null mice developed hypersensitivity to cold, axial discomfort, age-dependent motor impairment, age-dependent increases in sensory innervation in and around the IVDs, age-dependent upregulation of CGRP and neuropeptide-Y in dorsal root ganglia, and age-dependent upregulation of CGRP, microglia, and astrocytes in the spinal cord dorsal horn. Increased innervation of degenerating IVDs by sensory nerve fibers and the neuroplasticity in sensory neurons and spinal cord could contribute to the underlying pathobiology of chronic discogenic LBP. N/A.

  5. A Three-dimensional Simulation of a Magnetized Accretion Disk: Fast Funnel Accretion onto a Weakly Magnetized Star

    Science.gov (United States)

    Takasao, Shinsuke; Tomida, Kengo; Iwasaki, Kazunari; Suzuki, Takeru K.

    2018-04-01

    We present the results of a global, three-dimensional magnetohydrodynamics simulation of an accretion disk with a rotating, weakly magnetized central star. The disk is threaded by a weak, large-scale poloidal magnetic field, and the central star has no strong stellar magnetosphere initially. Our simulation investigates the structure of the accretion flows from a turbulent accretion disk onto the star. The simulation reveals that fast accretion onto the star at high latitudes occurs even without a stellar magnetosphere. We find that the failed disk wind becomes the fast, high-latitude accretion as a result of angular momentum exchange mediated by magnetic fields well above the disk, where the Lorentz force that decelerates the rotational motion of gas can be comparable to the centrifugal force. Unlike the classical magnetospheric accretion scenario, fast accretion streams are not guided by magnetic fields of the stellar magnetosphere. Nevertheless, the accretion velocity reaches the free-fall velocity at the stellar surface due to the efficient angular momentum loss at a distant place from the star. This study provides a possible explanation why Herbig Ae/Be stars whose magnetic fields are generally not strong enough to form magnetospheres also show indications of fast accretion. A magnetically driven jet is not formed from the disk in our model. The differential rotation cannot generate sufficiently strong magnetic fields for the jet acceleration because the Parker instability interrupts the field amplification.

  6. The metallicity distribution of stars in the Galactic bulge and disc

    Science.gov (United States)

    Koeppen, J.; Arimoto, N.

    1989-06-01

    The chemical evolution of the three-component system of halo-bulge-disc is calculated. If the bulge accretes primordial halo matter quickly and forms stars rapidly before the gas is ejected by a galactic wind after 10 to the 9th yr, the metallicity distribution of the bulge K-giants (Rich, 1988) is reproduced. The metal-enriched matter in a wind from the bulge is mixed with the halo gas which is accreted into the disc. The metallicity distribution of the G-dwarfs and Twarog's (1980) age-metallicity relation in the solar neighborhood can be well reproduced by assuming reasonable bulge-to-disc mass ratio.

  7. Accretion onto a noncommutative geometry inspired black hole

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Rahul [Jamia Millia Islamia, Centre for Theoretical Physics, New Delhi (India); Ghosh, Sushant G. [Jamia Millia Islamia, Centre for Theoretical Physics, New Delhi (India); Jamia Millia Islamia, Multidisciplinary Centre for Advanced Research and Studies (MCARS), New Delhi (India); University of KwaZulu-Natal, Astrophysics and Cosmology Research Unit, School of Mathematics, Statistics and Computer Science, Durban (South Africa)

    2017-09-15

    The spherically symmetric accretion onto a noncommutative (NC) inspired Schwarzschild black hole is treated for a polytropic fluid. The critical accretion rate M, sonic speed a{sub s} and other flow parameters are generalized for the NC inspired static black hole and compared with the results obtained for the standard Schwarzschild black holes. Also explicit expressions for gas compression ratios and temperature profiles below the accretion radius and at the event horizon are derived. This analysis is a generalization of Michel's solution to the NC geometry. Owing to the NC corrected black hole, the accretion flow parameters also have been modified. It turns out that M ∼ M{sup 2} is still achievable but r{sub s} seems to be substantially decreased due to the NC effects. They in turn do affect the accretion process. (orig.)

  8. DZ Chamaeleontis: a bona fide photoevaporating disc

    Science.gov (United States)

    Canovas, H.; Montesinos, B.; Schreiber, M. R.; Cieza, L. A.; Eiroa, C.; Meeus, G.; de Boer, J.; Ménard, F.; Wahhaj, Z.; Riviere-Marichalar, P.; Olofsson, J.; Garufi, A.; Rebollido, I.; van Holstein, R. G.; Caceres, C.; Hardy, A.; Villaver, E.

    2018-02-01

    Context. DZ Cha is a weak-lined T Tauri star (WTTS) surrounded by a bright protoplanetary disc with evidence of inner disc clearing. Its narrow Hα line and infrared spectral energy distribution suggest that DZ Cha may be a photoevaporating disc. Aims: We aim to analyse the DZ Cha star + disc system to identify the mechanism driving the evolution of this object. Methods: We have analysed three epochs of high resolution optical spectroscopy, photometry from the UV up to the sub-mm regime, infrared spectroscopy, and J-band imaging polarimetry observations of DZ Cha. Results: Combining our analysis with previous studies we find no signatures of accretion in the Hα line profile in nine epochs covering a time baseline of 20 yr. The optical spectra are dominated by chromospheric emission lines, but they also show emission from the forbidden lines [SII] 4068 and [OI] 6300Å that indicate a disc outflow. The polarized images reveal a dust depleted cavity of 7 au in radius and two spiral-like features, and we derive a disc dust mass limit of Mdust 80 MJup) companions are detected down to 0.̋07 ( 8 au, projected). Conclusions: The negligible accretion rate, small cavity, and forbidden line emission strongly suggests that DZ Cha is currently at the initial stages of disc clearing by photoevaporation. At this point the inner disc has drained and the inner wall of the truncated outer disc is directly exposed to the stellar radiation. We argue that other mechanisms like planet formation or binarity cannot explain the observed properties of DZ Cha. The scarcity of objects like this one is in line with the dispersal timescale (≲105 yr) predicted by this theory. DZ Cha is therefore an ideal target to study the initial stages of photoevaporation. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 097.C-0536. Based on data obtained from the ESO Science Archive Facility under request number 250112.

  9. Accretion models of Sgr A*

    OpenAIRE

    Yuan, Feng

    2006-01-01

    The supermassive black hole in the center of our Galaxy, Sgr A*, is unique because the angular size of the black hole is the largest in the sky thus providing detailed boundary conditions on, and much less freedom for, accretion flow models. In this paper I review advection-dominated accretion flow (ADAF; another name is radiatively inefficient accretion flow) models for Sgr A*. This includes the developments and dynamics of ADAFs, and how to explain observational results including the multi-...

  10. X-shooter spectroscopy of young stellar objects in Lupus. Accretion properties of class II and transitional objects

    Science.gov (United States)

    Alcalá, J. M.; Manara, C. F.; Natta, A.; Frasca, A.; Testi, L.; Nisini, B.; Stelzer, B.; Williams, J. P.; Antoniucci, S.; Biazzo, K.; Covino, E.; Esposito, M.; Getman, F.; Rigliaco, E.

    2017-04-01

    The mass accretion rate, Ṁacc, is a key quantity for the understanding of the physical processes governing the evolution of accretion discs around young low-mass (M⋆ ≲ 2.0 M⊙) stars and substellar objects (YSOs). We present here the results of a study of the stellar and accretion properties of the (almost) complete sample of class II and transitional YSOs in the Lupus I, II, III and IV clouds, based on spectroscopic data acquired with the VLT/X-shooter spectrograph. Our study combines the dataset from our previous work with new observations of 55 additional objects. We have investigated 92 YSO candidates in total, 11 of which have been definitely identified with giant stars unrelated to Lupus. The stellar and accretion properties of the 81 bona fide YSOs, which represent more than 90% of the whole class II and transition disc YSO population in the aforementioned Lupus clouds, have been homogeneously and self-consistently derived, allowing for an unbiased study of accretion and its relationship with stellar parameters. The accretion luminosity, Lacc, increases with the stellar luminosity, L⋆, with an overall slope of 1.6, similar but with a smaller scatter than in previous studies. There is a significant lack of strong accretors below L⋆ ≈ 0.1 L⊙, where Lacc is always lower than 0.01 L⋆. We argue that the Lacc - L⋆ slope is not due to observational biases, but is a true property of the Lupus YSOs. The log Ṁacc - log M⋆ correlation shows a statistically significant evidence of a break, with a steeper relation for M⋆ ≲ 0.2 M⊙ and a flatter slope for higher masses. The bimodality of the Ṁacc - M⋆ relation is confirmed with four different evolutionary models used to derive the stellar mass. The bimodal behaviour of the observed relationship supports the importance of modelling self-gravity in the early evolution of the more massive discs, but other processes, such as photo-evaporation and planet formation during the YSO's lifetime, may

  11. Genetic association studies in lumbar disc degeneration

    DEFF Research Database (Denmark)

    Eskola, Pasi J; Lemmelä, Susanna; Kjaer, Per

    2012-01-01

    Low back pain is associated with lumbar disc degeneration, which is mainly due to genetic predisposition. The objective of this study was to perform a systematic review to evaluate genetic association studies in lumbar disc degeneration as defined on magnetic resonance imaging (MRI) in humans....

  12. Black hole spin dependence of general relativistic multi-transonic accretion close to the horizon

    Czech Academy of Sciences Publication Activity Database

    Das, T. K.; Nag, S.; Hedge, S.; Bhattacharya, S.; Maity, I.; Czerny, B.; Barai, P.; Wiita, P. J.; Karas, Vladimír; Naskar, T.

    2015-01-01

    Roč. 37, May (2015), s. 81-104 ISSN 1384-1076 R&D Projects: GA ČR(CZ) GC13-00070J Institutional support: RVO:67985815 Keywords : black hole s * accretion discs Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.085, year: 2015

  13. Black hole accretion rings revealed by future X-ray spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Sochora, Vjačeslav; Karas, Vladimír; Svoboda, Jiří; Dovčiak, Michal

    2011-01-01

    Roč. 418, č. 1 (2011), s. 276-283 ISSN 0035-8711 R&D Projects: GA ČR GA205/07/0052; GA MŠk ME09036 Institutional research plan: CEZ:AV0Z10030501 Keywords : black hole s * accretion discs Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.900, year: 2011

  14. Angular momentum transfer in primordial discs and the rotation of the first stars

    Science.gov (United States)

    Hirano, Shingo; Bromm, Volker

    2018-02-01

    We investigate the rotation velocity of the first stars by modelling the angular momentum transfer in the primordial accretion disc. Assessing the impact of magnetic braking, we consider the transition in angular momentum transport mode at the Alfvén radius, from the dynamically dominated free-fall accretion to the magnetically dominated solid-body one. The accreting protostar at the centre of the primordial star-forming cloud rotates with close to breakup speed in the case without magnetic fields. Considering a physically-motivated model for small-scale turbulent dynamo amplification, we find that stellar rotation speed quickly declines if a large fraction of the initial turbulent energy is converted to magnetic energy (≳ 0.14). Alternatively, if the dynamo process were inefficient, for amplification due to flux-freezing, stars would become slow rotators if the pre-galactic magnetic field strength is above a critical value, ≃ 10-8.2 G, evaluated at a scale of nH = 1 cm-3, which is significantly higher than plausible cosmological seed values (˜10-15 G). Because of the rapid decline of the stellar rotational speed over a narrow range in model parameters, the first stars encounter a bimodal fate: rapid rotation at almost the breakup level, or the near absence of any rotation.

  15. Angular momentum transfer in primordial discs and the rotation of the first stars

    Science.gov (United States)

    Hirano, Shingo; Bromm, Volker

    2018-05-01

    We investigate the rotation velocity of the first stars by modelling the angular momentum transfer in the primordial accretion disc. Assessing the impact of magnetic braking, we consider the transition in angular momentum transport mode at the Alfvén radius, from the dynamically dominated free-fall accretion to the magnetically dominated solid-body one. The accreting protostar at the centre of the primordial star-forming cloud rotates with close to breakup speed in the case without magnetic fields. Considering a physically motivated model for small-scale turbulent dynamo amplification, we find that stellar rotation speed quickly declines if a large fraction of the initial turbulent energy is converted to magnetic energy (≳ 0.14). Alternatively, if the dynamo process were inefficient, for amplification due to flux freezing, stars would become slow rotators if the pre-galactic magnetic field strength is above a critical value, ≃10-8.2 G, evaluated at a scale of nH = 1 cm-3, which is significantly higher than plausible cosmological seed values (˜10-15 G). Because of the rapid decline of the stellar rotational speed over a narrow range in model parameters, the first stars encounter a bimodal fate: rapid rotation at almost the breakup level, or the near absence of any rotation.

  16. The Actual Level of Symptomatic Soft Disc Herniation in Patients with Cervical Disc Herniation.

    Science.gov (United States)

    Choi, Su Yong; Lee, Sang Gu; Kim, Woo Kyung; Son, Seong; Jeong, Tae Seok

    2015-09-01

    The aim of this study was to predict the relationship between the symptomatic disc herniation level and the osteophyte level or decreased disc height in patients with cervical disc herniation. Between January 2011 and December 2012, 69 patients with an osteophyte of the cervical spine underwent surgery at a single center due to soft cervical disc herniation. Data including soft disc herniation level, osteophyte level in the posterior vertebral margin, Cobb's angle, and symptom duration were retrospectively assessed. The patients were divided into three groups according to the relationship between the degenerative change level and the level of reported symptoms. Among the 69 patients, 48 (69.6%) showed a match between osteophyte level and soft disc herniation level. Disc herniation occurred at the adjacent segment to degenerative osteophyte level in 12 patients (17.4%) and at both the adjacent and the osteophyte level in nine (13.0%). There was no significant difference in Cobb's angle or duration among the three groups. Osteophyte type was not significant. The mean disc height of the prominent degenerative change level group was lower than the adjacent segment level, but this was not significant. Soft cervical disc herniation usually occurs at the level an osteophyte forms. However, it may also occur at segments adjacent to that of the osteophyte level. Therefore, in patients with cervical disc herniation, although a prominent osteophyte alone may appear on plain radiography, we must suspect the presence of soft disc herniation at other levels.

  17. Stability of black hole accretion disks

    Directory of Open Access Journals (Sweden)

    Czerny B.

    2012-12-01

    Full Text Available We discuss the issues of stability of accretion disks that may undergo the limit-cycle oscillations due to the two main types of thermal-viscous instabilities. These are induced either by the domination of radiation pressure in the innermost regions close to the central black hole, or by the partial ionization of hydrogen in the zone of appropriate temperatures. These physical processes may lead to the intermittent activity in AGN on timescales between hundreds and millions of years. We list a number of observational facts that support the idea of the cyclic activity in high accretion rate sources. We conclude however that the observed features of quasars may provide only indirect signatures of the underlying instabilities. Also, the support from the sources with stellar mass black holes, whose variability timescales are observationally feasible, is limited to a few cases of the microquasars. Therefore we consider a number of plausible mechanisms of stabilization of the limit cycle oscillations in high accretion rate accretion disks. The newly found is the stabilizing effect of the stochastic viscosity fluctuations.

  18. DIGIT survey of far-infrared lines from protoplanetary discs. II. CO

    Science.gov (United States)

    Meeus, Gwendolyn; Salyk, Colette; Bruderer, Simon; Fedele, Davide; Maaskant, Koen; Evans, Neal J.; van Dishoeck, Ewine F.; Montesinos, Benjamin; Herczeg, Greg; Bouwman, Jeroen; Green, Joel D.; Dominik, Carsten; Henning, Thomas; Vicente, Silvia

    2013-11-01

    CO is an important component of a protoplanetary disc as it is one of the most abundant gas phase species. Furthermore, observations of CO transitions can be used as a diagnostic of the gas, tracing conditions in both the inner and outer disc. We present Herschel/PACS spectroscopy of a sample of 22 Herbig Ae/Be (HAEBEs) and eight T Tauri stars (TTS), covering the pure rotational CO transitions from J = 14 → 13 up to J = 49 → 48. CO is detected in only five HAEBEs, namely AB Aur, HD 36112, HD 97048, HD 100546, and IRS 48, and in four TTS, namely AS 205, S CrA, RU Lup, and DG Tau. The highest transition detected is J = 36 → 35 with Eup of 3669 K, seen in HD 100546 and DG Tau. We construct rotational diagrams for the discs with at least three CO detections to derive Trot and find average temperatures of 270 K for the HAEBEs and 485 K for the TTS. The HD 100546 star requires an extra temperature component at Trot ~ 900-1000 K, suggesting a range of temperatures in its disc atmosphere, which is consistent with thermo-chemical disc models. In HAEBEs, the objects with CO detections all have flared discs in which the gas and dust are thermally decoupled. We use a small model grid to analyse our observations and find that an increased amount of flaring means higher line flux, as it increases the mass in warm gas. CO is not detected in our flat discs as the emission is below the detection limit. We find that HAEBE sources with CO detections have high LUV and strong PAH emission, which is again connected to the heating of the gas. In TTS, the objects with CO detections are all sources with evidence of a disc wind or outflow. For both groups of objects, sources with CO detections generally have high UV luminosity (either stellar in HAEBEs or due to accretion in TTS), but this is not a sufficient condition for the detection of the far-IR CO lines. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and

  19. Formation of precessing jets by tilted black hole discs in 3D general relativistic MHD simulations

    Science.gov (United States)

    Liska, M.; Hesp, C.; Tchekhovskoy, A.; Ingram, A.; van der Klis, M.; Markoff, S.

    2018-02-01

    Gas falling into a black hole (BH) from large distances is unaware of BH spin direction, and misalignment between the accretion disc and BH spin is expected to be common. However, the physics of tilted discs (e.g. angular momentum transport and jet formation) is poorly understood. Using our new GPU-accelerated code H-AMR, we performed 3D general relativistic magnetohydrodynamic simulations of tilted thick accretion discs around rapidly spinning BHs, at the highest resolution to date. We explored the limit where disc thermal pressure dominates magnetic pressure, and showed for the first time that, for different magnetic field strengths on the BH, these flows launch magnetized relativistic jets propagating along the rotation axis of the tilted disc (rather than of the BH). If strong large-scale magnetic flux reaches the BH, it bends the inner few gravitational radii of the disc and jets into partial alignment with the BH spin. On longer time-scales, the simulated disc-jet system as a whole undergoes Lense-Thirring precession and approaches alignment, demonstrating for the first time that jets can be used as probes of disc precession. When the disc turbulence is well resolved, our isolated discs spread out, causing both the alignment and precession to slow down.

  20. Evolution and precession of accretion disk in tidal disruption events

    Directory of Open Access Journals (Sweden)

    Matzner C.D.

    2012-12-01

    Full Text Available In a supermassive black hole (BH tidal disruption event (TDE, the tidally disrupted star feeds the BH via an accretion disk. Most often it is assumed that the accretion rate history, hence the emission light curve, tracks the rate at which new debris mass falls back onto the disk, notably the t−5/3 power law. But this is not the case when the disk evolution due to viscous spreading - the driving force for accretion - is carefully considered. We construct a simple analytical model that comprehensively describes the accretion rate history across 4 different phases of the disk evolution, in the presence of mass fallback and disk wind loss. Accretion rate evolves differently in those phases which are governed by how the disk heat energy is carried away, early on by advection and later by radiation. The accretion rate can decline as steeply as t−5/3 only if copious disk wind loss is present during the early advection-cooled phase. Later, the accretion rate history is t−8/7 or shallower. These have great implications on the TDE flare light curve. A TDE accretion disk is most likely misaligned with the equatorial plane of the spinning BH. Moreover, in the TDE the accretion rate is super- or near-Eddington thus the disk is geometrically thick, for which case the BH’s frame dragging effect may cause the disk precess as a solid body, which may manifest itself as quasi-periodic signal in the TDE light curve. Our disk evolution model predicts the disk precession period increases with time, typically as ∝ t. The results are applied to the recently jetted TDE flare Swift transient J1644 + 57 which shows numerous, quasi-periodic dips in its long-term X-ray light curve. As the current TDE sample increases, the identification of the disk precession signature provides a unique way of measuring BH spin and studying BH accretion physics.

  1. Cold gas accretion in galaxies

    NARCIS (Netherlands)

    Sancisi, Renzo; Fraternali, Filippo; Oosterloo, Tom; van der Hulst, Thijs

    Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing or recent accretion: (1) A large number of galaxies are accompanied by

  2. Vertebral osteomyelitis without disc involvement

    Energy Technology Data Exchange (ETDEWEB)

    Kamani, I.; Syed, I.; Saifuddin, A. E-mail: asaifuddin@aol.com; Green, R.; MacSweeney, F

    2004-10-01

    Vertebral osteomyelitis is most commonly due to pyogenic or granulomatous infection and typically results in the combined involvement of the intervertebral disc and adjacent vertebral bodies. Non-infective causes include the related conditions of chronic recurrent multifocal osteomyelitis (CRMO) and SAPHO (synovitis, acne, pustulosis, hyperostosis, and osteitis) syndrome. Occasionally, these conditions may present purely within the vertebral body, resulting in various combinations of vertebral marrow oedema and sclerosis, destructive lesions of the vertebral body and pathological vertebral collapse, thus mimicking neoplastic disease. This review illustrates the imaging features of vertebral osteomyelitis without disc involvement, with emphasis on magnetic resonance imaging (MRI) findings.

  3. Minimum weight design of inhomogeneous rotating discs

    International Nuclear Information System (INIS)

    Jahed, Hamid; Farshi, Behrooz; Bidabadi, Jalal

    2005-01-01

    There are numerous applications for gas turbine discs in the aerospace industry such as in turbojet engines. These discs normally work under high temperatures while subjected to high angular velocities. Minimizing the weight of such items in aerospace applications results in benefits such as low dead weights and lower costs. High speed of rotation causes large centrifugal forces in a disc and simultaneous application of high temperatures reduces disc material strength. Thus, the latter effects tend to increase deformations of the disc under the applied loads. In order to obtain a reliable disc analysis and arrive at the corresponding correct stress distribution, solutions should consider changes in material properties due to the temperature field throughout the disc. To achieve this goal, an inhomogeneous disc model with variable thickness is considered. Using the variable material properties method, stresses are obtained for the disc under rotation and a steady temperature field. In this paper this is done by modelling the rotating disc as a series of rings of different but constant properties. The optimum disc profile is arrived at by sequentially proportioning the thicknesses of each ring to satisfy the stress requirements. This method vis-a-vis a mathematical programming procedure for optimization shows several advantages. Firstly, it is simple iterative proportioning in each design cycle not requiring involved mathematical operations. Secondly, due to its simplicity it alleviates the necessity of certain simplifications that are common in so-called rigorous mathematical procedures. The results obtained, compared to those published in the literature show agreement and superiority. A further advantage of the proposed method is the independence of the end results from the initially assumed point in the iterative design routine, unlike most methods published so far

  4. Herniated Cervical Disc

    Science.gov (United States)

    ... and inflammation that occur as a result of disc herniation. These include aspirin, ibuprofen, naproxen and a variety ... many factors including the exact location of the disc herniation and the experience and preference of the surgeon. ...

  5. Spontaneous Regression of Herniated Lumbar Disc with New Disc Protrusion in the Adjacent Level.

    Science.gov (United States)

    Hakan, Tayfun; Gürcan, Serkan

    2016-01-01

    Spontaneous regression of herniated lumbar discs was reported occasionally. The mechanisms proposed for regression of disc herniation are still incomplete. This paper describes and discusses a case of spontaneous regression of herniated lumbar discs with a new disc protrusion in the adjacent level. A 41-year-old man was admitted with radiating pain and numbness in the left lower extremity with a left posterolateral disc extrusion at L5-S1 level. He was admitted to hospital with low back pain due to disc herniation caudally immigrating at L4-5 level three years ago. He refused the surgical intervention that was offered and was treated conservatively at that time. He had no neurological deficit and a history of spontaneous regression of the extruded lumbar disc; so, a conservative therapy, including bed rest, physical therapy, nonsteroidal anti-inflammatory drugs, and analgesics, was advised. In conclusion, herniated lumbar disc fragments may regress spontaneously. Reports are prone to advise conservative treatment for extruded or sequestrated lumbar disc herniations. However, these patients should be followed up closely; new herniation at adjacent/different level may occur. Furthermore, it is important to know which herniated disk should be removed and which should be treated conservatively, because disc herniation may cause serious complications as muscle weakness and cauda equine syndrome.

  6. Core-assisted gas capture instability: a new mode of giant planet formation by gravitationally unstable discs

    OpenAIRE

    Nayakshin, Sergei; Helled, Ravit; Boley, Aaron C.

    2014-01-01

    Giant planet formation in the core accretion (CA) paradigm is predicated by the formation of a core, assembled by the coagulation of grains and later by planetesimals within a protoplanetary disc. In contrast, in the disc instability paradigm, giant planet formation is believed to be independent of core formation: massive self-gravitating gas fragments cool radiatively and collapse as a whole. We show that giant planet formation in the disc instability model may be also enhanced by core forma...

  7. Radially truncated galactic discs

    NARCIS (Netherlands)

    Grijs, R. de; Kregel, M.; Wesson, K H

    2000-01-01

    Abstract: We present the first results of a systematic analysis of radially truncatedexponential discs for four galaxies of a sample of disc-dominated edge-onspiral galaxies. Edge-on galaxies are very useful for the study of truncatedgalactic discs, since we can follow their light distributions out

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

    DEFF Research Database (Denmark)

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

    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...

  9. X-ray and UV correlation in the quiescent emission of Cen X-4, evidence of accretion and reprocessing

    Directory of Open Access Journals (Sweden)

    Bernardini F.

    2014-01-01

    Full Text Available We conducted the first long-term (60 days, multiwavelength (optical, ultraviolet, and X-ray simultaneous monitoring of Cen X-4 with daily Swift observations, with the goal of understanding variability in the low mass X-ray binary Cen X-4 during quiescence. We found Cen X-4 to be highly variable in all energy bands on timescales from days to months, with the strongest quiescent variability a factor of 22 drop in the X-ray count rate in only 4 days. The X-ray, UV and optical (V band emission are correlated on timescales down to less than 110 s. The shape of the correlation is a power law with index γ about 0.2–0.6. The X-ray spectrum is well fitted by a hydrogen NS atmosphere (kT = 59 − 80 eV and a power law (with spectral index Γ = 1.4 − 2.0, with the spectral shape remaining constant as the flux varies. Both components vary in tandem, with each responsible for about 50% of the total X-ray flux, implying that they are physically linked. We conclude that the X-rays are likely generated by matter accreting down to the NS surface. Moreover, based on the short timescale of the correlation, we also unambiguously demonstrate that the UV emission can not be due to either thermal emission from the stream impact point, or a standard optically thick, geometrically thin disc. The spectral energy distribution shows a small UV emitting region, too hot to arise from the accretion disk, that we identified as a hot spot on the companion star. Therefore, the UV emission is most likely produced by reprocessing from the companion star, indeed the vertical size of the disc is small and can only reprocess a marginal fraction of the X-ray emission. We also found the accretion disc in quiescence to likely be UV faint, with a minimal contribution to the whole UV flux.

  10. Helicopter rotor noise investigation during ice accretion

    Science.gov (United States)

    Cheng, Baofeng

    An investigation of helicopter rotor noise during ice accretion is conducted using experimental, theoretical, and numerical methods. This research is the acoustic part of a joint helicopter rotor icing physics, modeling, and detection project at The Pennsylvania State University Vertical Lift Research Center of Excellence (VLRCOE). The current research aims to provide acoustic insight and understanding of the rotor icing physics and investigate the feasibility of detecting rotor icing through noise measurements, especially at the early stage of ice accretion. All helicopter main rotor noise source mechanisms and their change during ice accretion are discussed. Changes of the thickness noise, steady loading noise, and especially the turbulent boundary layer - trailing edge (TBL-TE) noise due to ice accretion are identified and studied. The change of the discrete frequency noise (thickness noise and steady loading noise) due to ice accretion is calculated by using PSU-WOPWOP, an advanced rotorcraft acoustic prediction code. The change is noticeable, but too small to be used in icing detection. The small thickness noise change is due to the small volume of the accreted ice compared to that of the entire blade, although a large iced airfoil shape is used. For the loading noise calculation, two simplified methods are used to generate the loading on the rotor blades, which is the input for the loading noise calculation: 1) compact loading from blade element momentum theory, icing effects are considered by increasing the drag coefficient; and 2) pressure loading from the 2-D CFD simulation, icing effects are considered by using the iced airfoil shape. Comprehensive rotor broadband noise measurements are carried out on rotor blades with different roughness sizes and rotation speeds in two facilities: the Adverse Environment Rotor Test Stand (AERTS) facility at The Pennsylvania State University, and The University of Maryland Acoustic Chamber (UMAC). In both facilities the

  11. Accretion in Saturn's F Ring

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  13. Correlating nonlinear properties with spectral states of RXTE data: Possible observational evidences for four different accretion modes around compact objects

    Science.gov (United States)

    Adegoke, Oluwashina; Dhang, Prasun; Mukhopadhyay, Banibrata; Ramadevi, M. C.; Bhattacharya, Debbijoy

    2018-02-01

    By analyzing the time series of RXTE/PCA data, the nonlinear variabilities of compact sources have been repeatedly established. Depending on the variation in temporal classes, compact sources exhibit different nonlinear features. Sometimes they show low correlation/fractal dimension, but in other classes or intervals of time they exhibit stochastic nature. This could be because the accretion flow around a compact object is a nonlinear general relativistic system involving magnetohydrodynamics. However, the more conventional way of addressing a compact source is the analysis of its spectral state. Therefore, the question arises: What is the connection of nonlinearity to the underlying spectral properties of the flow when the nonlinear properties are related to the associated transport mechanisms describing the geometry of the flow? The present work is aimed at addressing this question. Based on the connection between observed spectral and nonlinear (time series) properties of two X-ray binaries: GRS 1915+105 and Sco X-1, we attempt to diagnose the underlying accretion modes of the sources in terms of known accretion classes, namely, Keplerian disc, slim disc, advection dominated accretion flow (ADAF) and general advective accretion flow (GAAF). We explore the possible transition of the sources from one accretion mode to others with time. We further argue that the accretion rate must play an important role in transition between these modes.

  14. Neutron star accretion and the neutrino fireball

    International Nuclear Information System (INIS)

    Colgate, S.A.; Herant, M.E.; Benz, W.

    1991-01-01

    The mixing necessary to explain the ''Fe'' line widths and possibly the observed red shifts of 1987A is explained in terms of large scale, entropy conserving, up and down flows (calculated with a smooth particle 2-D code) taking place between the neutron star and the explosion shock wave due to the gravity and neutrino deposition. Depending upon conditions of entropy and mass flux further accretion takes place in single events, similar to relaxation oscillator, fed by the downward flows of low entropy matter. The shock, in turn, is driven by the upflow of the buoyant high entropy bubbles. Some accretion events will reach a temperature high enough to create a neutrino ''fireball,'' a region hot enough, 11 Mev, so as to be partially opaque to its own (neutrino) radiation. The continuing neutrino deposition drives the explosion shock until the entropy of matter flowing downwards onto the neutron star is high enough to prevent further accretion. This process should result in a robust supernova explosion

  15. A COMMON SOURCE OF ACCRETION DISK TILT

    International Nuclear Information System (INIS)

    Montgomery, M. M.; Martin, E. L.

    2010-01-01

    Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source that causes and maintains disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through the disk's center of mass. The disk responds to lift by pitching around the disk's line of nodes. If the gas stream flow ebbs, then lift also ebbs and the disk attempts to return to its original orientation. To first approximation, lift does not depend on magnetic fields or radiation sources but does depend on the mass and the surface area of the disk. Also, for disk tilt to be initiated, a minimum mass transfer rate must be exceeded. For example, a 10 -11 M sun disk around a 0.8 M sun compact central object requires a mass transfer rate greater than ∼ 8 x 10 -11 M sun yr -1 , a value well below the known mass transfer rates in cataclysmic variable dwarf novae systems that retrogradely precess and exhibit negative superhumps in their light curves and a value well below mass transfer rates in protostellar-forming systems.

  16. On accretion from an inhomogeneous medium

    International Nuclear Information System (INIS)

    Davies, R.E.; Pringle, J.E.

    1980-01-01

    Hypersonic accretion flow in two dimensions from an infinite medium which contains a small density and/or velocity gradient is considered. To first order in rsub(a)/h, where rsub(a) is the accretion radius and h the scale of the gradient, the accretion rate is unaffected and the accreted angular momentum is zero. Thus previous estimates of the amount of angular momentum accreted may severely overestimate the actual value. (author)

  17. Highly Magnetized Accreting Pulsars: Are There Accreting Magnetars?

    Directory of Open Access Journals (Sweden)

    Pere Blay

    2014-12-01

    Full Text Available 2S 0114+650, GX 301-2, IGR J16358-4726, X Per, 4U 2206+54, SXP 1062, and 3A 1954+319 are thought to possess high magnetic elds. They have recently been named accreting magnetars, or highly magnetized accreting pulsars. In this work their properties are reviewed. Within the context of their observational properties (mainly from INTEGRAL data, and the recent models of accretion onto highly magnetized neutron stars, their similarities and dierences are analyzed. The aim is to find a common framework to understand the evolution (in terms of past and present history of these sources, and to establish the basis of a possible new kind of accreting sources. Two of these sources, namely X Per and 4U 2206+54, contain a massive main-sequence companion, while the rest are supergiant X-ray binaries or symbiotic systems. The variety of astrophysical scenarios represented by this set is wide, therefore the study of these systems is also important in order to establish commonalities between the dierent types of accreting X-ray pulsars and to study the possible evolutionary links between them.

  18. Intervertebral disc calcifications in children.

    Science.gov (United States)

    Beluffi, G; Fiori, P; Sileo, C

    2009-03-01

    This study was done to assess the presence of both asymptomatic and symptomatic intervertebral disc calcifications in a large paediatric population. We retrospectively reviewed the radiographs taken during the past 26 years in children (age 0-18 years) undergoing imaging of the spine or of other body segments in which the spine was adequately depicted, to determine possible intervertebral disc calcifications. The following clinical evaluation was extrapolated from the patients' charts: presence of spinal symptoms, history of trauma, suspected or clinically evident scoliosis, suspected or clinically evident syndromes, bone dysplasias, and pre- or postoperative chest or abdominal X-rays. We detected intervertebral disc calcifications in six patients only. Five calcifications were asymptomatic (one newborn baby with Patau syndrome; three patients studied to rule out scoliosis, hypochondroplasia and syndromic traits; one for dyspnoea due to sunflower seeds inhalation). Only one was symptomatic, with acute neck pain. Calcifications varied in number from one in one patient to two to five in the others. Apart from the calcification in the patient with cervical pain, all calcifications were asymptomatic and constituted an incidental finding (particularly those detected at the thoracic level in the patient studied for sunflower-seed inhalation). Calcification shapes were either linear or round. Our series confirms that intervertebral disc calcifications are a rare finding in childhood and should not be a source of concern: symptomatic calcifications tend to regress spontaneously within a short time with or without therapy and immobilisation, whereas asymptomatic calcifications may last for years but disappear before the age of 20 years. Only very few cases, such as those of medullary compression or severe dysphagia due to anterior herniation of cervical discs, may require surgical procedures.

  19. Accretion Disks and Coronae in the X-Ray Flashlight

    Science.gov (United States)

    Degenaar, Nathalie; Ballantyne, David R.; Belloni, Tomaso; Chakraborty, Manoneeta; Chen, Yu-Peng; Ji, Long; Kretschmar, Peter; Kuulkers, Erik; Li, Jian; Maccarone, Thomas J.; Malzac, Julien; Zhang, Shu; Zhang, Shuang-Nan

    2018-02-01

    Plasma accreted onto the surface of a neutron star can ignite due to unstable thermonuclear burning and produce a bright flash of X-ray emission called a Type-I X-ray burst. Such events are very common; thousands have been observed to date from over a hundred accreting neutron stars. The intense, often Eddington-limited, radiation generated in these thermonuclear explosions can have a discernible effect on the surrounding accretion flow that consists of an accretion disk and a hot electron corona. Type-I X-ray bursts can therefore serve as direct, repeating probes of the internal dynamics of the accretion process. In this work we review and interpret the observational evidence for the impact that Type-I X-ray bursts have on accretion disks and coronae. We also provide an outlook of how to make further progress in this research field with prospective experiments and analysis techniques, and by exploiting the technical capabilities of the new and concept X-ray missions ASTROSAT, NICER, Insight-HXMT, eXTP, and STROBE-X.

  20. Is the disc thermal state controlling the Blandford & Znajek/Blandford & Payne jet dichotomy?

    Directory of Open Access Journals (Sweden)

    Ferreira Jonathan

    2013-12-01

    Full Text Available It is generally assumed that Blandford & Payne jets can carry a significant fraction of the accretion power released in the underlying disc. But this fraction actually strongly depends on the disc aspect ratio h/r, hence on the disc thermal properties. In fact, Jet Emitting discs (JEDs cannot power BP-like jets if they are thicker than h/r ≃ 0.2. On the other hand, the power of Blandford & Znajek jets depends mostly on the magnitude of the vertical magnetic field Bz. If this magnetic field is dragged in by the accretion flow, then its magnitude depends also on the disc aspect ratio and the BZ jet maximum power is achieved with Magnetically Arrested Discs (MADs. If the innermost disc regions are geometrically thin or slim, they are in a JED state with both BP and BZ jets launched. It is shown that the BZ jet acts only as a highly relativistic and shinning spine, carrying a tiny fraction of the overall jet power. If the innermost disc regions are geometrically thick, they are in a MAD state where only BZ jets are allowed. We expect quite di↵erent jet morphologies in the two cases.

  1. Predictions for the reverberating spectral line signal from a newly formed black hole accretion disk: case of tidal disruption flares

    Czech Academy of Sciences Publication Activity Database

    Zhang, W.; Yu, W.; Karas, Vladimír; Dovčiak, Michal

    2015-01-01

    Roč. 807, č. 89 (2015), s. 1-12 ISSN 0004-637X R&D Projects: GA MŠk(CZ) LH14049; GA ČR(CZ) GC13-00070J Institutional support: RVO:67985815 Keywords : black hole s * accretion discs Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.909, year: 2015

  2. Computer assisted characterization of cervical intervertebral disc degeneration in MRI

    Science.gov (United States)

    Michopoulou, S.; Boniatis, I.; Costaridou, L.; Cavouras, D.; Panagiotopoulos, E.; Panayiotakis, G.

    2009-05-01

    A texture-based pattern recognition system is proposed for the automatic characterization of cervical intervertebral disc degeneration from saggital magnetic resonance images of the spine. A case sample of 50 manually segmented ROIs, corresponding to 25 normal and 25 degenerated discs, was analyzed and textural features were generated from each disc-ROI. Student's t-test verified the existence of statistically significant differences between textural feature values generated from normal and degenerated discs. This finding is indicative of disc image texture differentiation due to the degeneration of the disc. The generated features were employed in the design of a pattern recognition system based on the Least Squares Minimum Distance classifier. The system achieved a classification accuracy of 94{%} and it may be of value to physicians for the assessment of cervical intervertebral disc degeneration in MRI.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  5. Quebec Back Pain Disability Scale, Low Back Outcome Score and revised Oswestry low back pain disability scale for patients with low back pain due to degenerative disc disease: evaluation of Polish versions.

    Science.gov (United States)

    Misterska, Ewa; Jankowski, Roman; Glowacki, Maciej

    2011-12-15

    Evaluation and comparison of translated and culturally adapted self-reported measurements. The aim of this prospective study was to cross-culturally adapt the Polish versions of Revised Oswestry Disability Index (RODI-PL), Quebec Back Pain Disability Scale (QDS-PL), and the Low Back Outcome Score (LBOS-PL). The application of instruments in English, which have undergone translation must be subjected to validation studies. Such studies are necessary above all for instruments that have been adapted to establish their value and usefulness in studies of patient populations where English is not the native language. The translation was carried out according to International Quality of Life Association (IQOLA) Project and consisted of the following stages: translation, synthesis of the translations, back translation, expert committee, and testing of the prefinal versions of questionnaires. Eighty-five consecutive patients with low back pain due to spinal disc herniation and degenerative changes completed the QDS-PL, RODI-PL, LBOS-PL, and a Visual Analogue Scale twice within 2-day intervals. Mean duration of LBP was 45.9 months SD 55.5. The evaluation of degenerative changes in the lumbar region was carried out according to the Modic scale. Twenty-nine patients were categorized at type I, 4 patients were registered as type II, and 52 patients were type III. Cronbach α values for the LBOS-PL equaled 0.77, for the RODI-PL 0.85, and 0.95 for the QDS-PL. Item-total correlation confirmed that all scales are internally consistent. Test-retest reliability was excellent for RODI-PL and QDS-PL, but poor for LBOS-PL (0.88, 0.93, and 0.34, respectively). All questionnaires were significantly intercorrelated. We identified the strongest correlation between QDS-PL and RODI-PL (0.823, P < 0.001). The statistically significant correlation was identified between the QDS-PL and Modic Classification (rS = 0.226 P = 0.038). QBPDS-PL and RODI-PL are reliable and valid. Furthermore

  6. Disc operational system

    International Nuclear Information System (INIS)

    Veretenov, V.Yu.; Volkov, A.I.; Gurevich, M.I.; Kozik, V.S.; Pod'yachev, E.I.; Shapiro, M.L.

    1974-01-01

    A disc operational system is proposed, which is based on the file structure and designed for use in a BESM-6 computer with the software system comprising a dispatcher DD-73 and a monitor 'Dubna'. The main distinguishing feature of the disc operational system is the decentralization of the file system. Each disc package is an independent file unaffected by the state of the other disc packages. The use of several disc packages is allowed. The above feature of the disc operational system makes it possible to simplify the language of communication with the system, to give the user the opportunity of controlling the file quite independently, and to simplify the maintenance of the discs by the computer personnel. One and the same disc can be simultaneously addressed by all problems in the processor (both mathematical and service). A single file, however, may be used in the recording mode by only one problem. The description presented is the instruction for users. It also describes special possibilities open to the system programmers [ru

  7. Intratracheal Seal Disc

    DEFF Research Database (Denmark)

    Christiansen, Karen J; Moeslund, Niels; Lauridsen, Henrik

    2017-01-01

    21, CT was repeated before euthanasia. The trachea and epidermis were excised en bloc for histopathological evaluation. RESULTS: Insertion and correct placement of the disc was unproblematic in all animals. CT at day 14 confirmed a clear airway, appropriate placement of the disc, and full closure...

  8. Protostellar accretion traced with chemistry

    DEFF Research Database (Denmark)

    Frimann, Søren; Jørgensen, Jes Kristian; Dunham, Michael M.

    2017-01-01

    . Our aim is to characterise protostellar accretion histories towards individual sources by utilising sublimation and freeze-out chemistry of CO. Methods. A sample of 24 embedded protostars are observed with the Submillimeter Array (SMA) in context of the large program "Mass Assembly of Stellar Systems...

  9. Angular momentum, accretion, and radial flows in chemodynamical models of spiral galaxies

    NARCIS (Netherlands)

    Pezzulli, G.; Fraternali, F.

    2016-01-01

    Gas accretion and radial flows are key ingredients of the chemical evolution of spiral galaxies. They are also tightly linked to each other (accretion drives radial flows due to angular momentum conservation) and should therefore be modeled simultaneously. We summarize an algorithm that can be used

  10. On the thickness of accretion curtains on magnetized compact objects from analysis of their fast aperiodic time variability.

    Science.gov (United States)

    Semena, Andrey

    It is widely accepted that accretion onto magnetized compact objects is channelled to some areas close to magnetic poles of the star. Thickness of this channelled accretion flow intimately depends on details of penetration of highly conducting plasma of the flow to the compact object magnetosphere, i.e. on magnetic diffusivity etc. Until now our knowledge of these plasma properties is scarce. In our work we present our attempts to estimate the thickness of the plasma flow on top of the magnetosphere from observations of accreting intermediate polars (magnetized white dwarfs). We show that properties of aperiodic noise of accreting intermediate polars can be used to put constrains on cooling time of hot plasma, heated in the standing shock wave above the WD surface. Estimates of the cooling time and the mass accretion rate provide us a tool to measure the density of post-shock plasma and the cross-sectional area of the accretion funnel at the WD surface. We have studied aperiodic noise of emission of one of the brightest intermediate polar EX Hya with the help of data in optical and X-ray energy bands. We put an upper limit on the plasma cooling timescale tau <0.2-0.5 sec, on the fractional area of the accretion curtain footprint f < 1.6 × 10(-4) . We show that measurements of accretion column footprints, combined with results of the eclipse mapping, can be used to obtain an upper limit on the penetration depth of the accretion disc plasma at the boundary of the magnetosphere, Delta r / r ≈ 10(-3) If the magnetospheres of accreting neutron stars have similar plasma penetration depths at their boundaries, we predict that footprints of their accretion columns should be very small, with fractional areas < 10(-6) .

  11. Fundamental Ice Crystal Accretion Physics Studies

    Science.gov (United States)

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

    2012-01-01

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

  12. Accretion effects on compact members of binary stars

    International Nuclear Information System (INIS)

    Spyrou, N.

    1988-01-01

    The change in the period of axial rotation and in the radius of a magnetized compact star in a binary system, induced by the accretion on it of mass with angular momentum from the surface of its non-compact companion is explored. No specific assumption is made concerning the accretion model, and the primary's interior is described by the Fermi-Dirac statistics for degenerate matter. The rate of change with time of the period and radius is expressed in terms of the compact primary's physical parameters and total absolute luminosity. The conditions are fully derived under which the above changes can be positive, negative or even vanish. In the case of the millisecond pulsars in binary X-ray sources the predicted values of the period time derivative, depending on the values of the accretion rate and the absolute luminosity, can be positive or negative - if not vanishing - and they fall absolutely in the range 10 -21 - 10 -17 ss -1 , in good agreement with current observational data. The corresponding rate of change of radius, either positive or negative, fall in the range of 10 -3 - 10 -1 cm y -1 . Finally, it is proved that the wellknown bursters can be explained by thermonuclear flash due to gravitational instability in the accreted matter, but their explanation as a result of direct contraction could be possible only for quite high accretion rates (>10 -7 M y -1 ). This last result indicates that, in contrast to the accretion-induced change in period, which can be of either sign irrespective of the primary's age, the accretion-induced non-catastrophic contraction is impossible, while according to recent results the contraction in general is possible for young compact objects. (author). 27 refs

  13. Disc-corona interaction in the heartbeat state of GRS 1915+105

    Science.gov (United States)

    Yan, Shu-Ping; Ji, Li; Liu, Si-Ming; Méndez, Mariano; Wang, Na; Li, Xiang-Dong; Qu, Jin-Lu; Sun, Wei; Ge, Ming-Yu; Liao, Jin-Yuan; Niu, Shu; Ding, Guo-Qiang; Liu, Qing-Zhong

    2018-02-01

    Timing analysis provides information about the dynamics of matter accreting on to neutron stars and black holes, and hence is crucial for studying the physics of the accretion flow around these objects. It is difficult, however, to associate the different variability components with each of the spectral components of the accretion flow. We apply several new methods to two Rossi X-ray Timing Explorer observations of the black hole binary GRS 1915+105 during its heartbeat state to explore the origin of the X-ray variability and the interactions of the accretion-flow components. We offer a promising window into the disc-corona interaction through analysing the formation regions of the disc aperiodic variabilities with different time-scales via comparing the corresponding transition energies of the amplitude-ratio spectra. In a previous paper, we analysed the Fourier power density as a function of energy and frequency to study the origin of the aperiodic variability, and combined that analysis with the phase lag as a function of frequency to derive a picture of the disc-corona interaction in this source. We here, for the first time, investigate the phase-lag as a function of energy and frequency, and display some interesting details of the disc-corona interaction. Besides, the results from the shape of amplitude-ratio spectrum and from several other aspects suggest that the quasi-periodic oscillation originates from the corona.

  14. Contrasting Accreting White Dwarf Pulsators with the ZZ Ceti Stars

    Science.gov (United States)

    Mukadam, A. S.; Szkody, P.; Gänsicke, B. T.; Pala, A.

    2017-03-01

    Understanding the similarities and differences between the accreting white dwarf pulsators and their non-interacting counterparts, the ZZ Ceti stars, will eventually help us deduce how accretion affects pulsations. ZZ Ceti stars pulsate in a narrow instability strip in the range 10800-12300 K due to H ionization in their pure H envelopes; their pulsation characteristics depend on their temperature and stellar mass. Models of accreting white dwarfs are found to be pulsationally unstable due to the H/HeI ionization zone, and even show a second instability strip around 15000 K due to HeII ionization. Both these strips are expected to merge for a He abundance higher than 0.48 to form a broad instability strip, which is consistent with the empirical determination of 10500-16000 K. Accreting pulsators undergo outbursts, during which the white dwarf is heated to temperatures well beyond the instability strip and is observed to cease pulsations. The white dwarf then cools to quiescence in a few years as its outer layers cool more than a million times faster than the evolutionary rate. This provides us with an exceptional opportunity to track the evolution of pulsations from the blue edge to quiescence in a few years, while ZZ Ceti stars evolve on Myr timescales. Some accreting pulsators have also been observed to cease pulsations without any apparent evidence of an outburst. This is a distinct difference between this class of pulsators and the non-interacting ZZ Ceti stars. While the ZZ Ceti instability strip is well sampled, the strip for the accreting white dwarfs is sparsely sampled and we hereby add two new potential discoveries to improve the statistics.

  15. Angular Momentum Transport in Quasi-Keplerian Accretion Disks ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Peter A. Becker. 3. 1Inter-University Center for Astronomy and Astrophysics, P.O Bag 4, Ganeshkhind,. Pune 411 007, India. e-mail: psubrama@iucaa.ernet.in. 2Dept. of Physics, University of Pune, .... ity η arises out of local effects, i.e., due to momentum exchange between neighboring annuli of the accretion disk, as with ...

  16. Accretion among preplanetary bodies : The many faces of runaway growth

    NARCIS (Netherlands)

    Ormel, C. W.; Dullemond, C. P.; Spaans, M.

    2010-01-01

    When preplanetary bodies reach proportions of similar to 1 km or larger in size, their accretion rate is enhanced due to gravitational focusing (GF). We have developed a new numerical model to calculate the collisional evolution of the gravitationally-enhanced growth stage. The numerical model is

  17. Radiatively-suppressed spherical accretion under relativistic radiative transfer

    Science.gov (United States)

    Fukue, Jun

    2018-03-01

    We numerically examine radiatively-suppressed relativistic spherical accretion flows on to a central object with mass M under Newtonian gravity and special relativity. We simultaneously solve both the relativistic radiative transfer equation and the relativistic hydrodynamical equations for spherically symmetric flows under the double iteration process in the case of the intermediate optical depth. We find that the accretion flow is suppressed, compared with the freefall case in the nonrelativistic regime. For example, in the case of accretion on to a luminous core with accretion luminosity L*, the freefall velocity v normalized by the speed of light c under the radiative force in the nonrelativistic regime is β (\\hat{r}) = v/c = -√{(1-Γ _*)/(\\hat{r}+1-Γ _*)}, where Γ* (≡ L*/LE, LE being the Eddington luminosity) is the Eddington parameter and \\hat{r} (= r/rS, rS being the Schwarzschild radius) the normalized radius, whereas the infall speed at the central core is ˜0.7β(1), irrespective of the mass-accretion rate. This is due to the relativistic effect; the comoving flux is enhanced by the advective flux. We briefly examine and discuss an isothermal case, where the emission takes place in the entire space.

  18. LUNAR ACCRETION FROM A ROCHE-INTERIOR FLUID DISK

    Energy Technology Data Exchange (ETDEWEB)

    Salmon, Julien; Canup, Robin M., E-mail: julien@boulder.swri.edu, E-mail: robin@boulder.swri.edu [Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302 (United States)

    2012-11-20

    We use a hybrid numerical approach to simulate the formation of the Moon from an impact-generated disk, consisting of a fluid model for the disk inside the Roche limit and an N-body code to describe accretion outside the Roche limit. As the inner disk spreads due to a thermally regulated viscosity, material is delivered across the Roche limit and accretes into moonlets that are added to the N-body simulation. Contrary to an accretion timescale of a few months obtained with prior pure N-body codes, here the final stage of the Moon's growth is controlled by the slow spreading of the inner disk, resulting in a total lunar accretion timescale of {approx}10{sup 2} years. It has been proposed that the inner disk may compositionally equilibrate with the Earth through diffusive mixing, which offers a potential explanation for the identical oxygen isotope compositions of the Earth and Moon. However, the mass fraction of the final Moon that is derived from the inner disk is limited by resonant torques between the disk and exterior growing moons. For initial disks containing <2.5 lunar masses (M{sub Last-Quarter-Moon }), we find that a final Moon with mass > 0.8 M{sub Last-Quarter-Moon} contains {<=}60% material derived from the inner disk, with this material preferentially delivered to the Moon at the end of its accretion.

  19. Solar neutrinos and solar accretion of interstellar matter

    International Nuclear Information System (INIS)

    Newman, M.J.; Talbot, R.J. Jr.

    1976-01-01

    It is argued that if the Hoyle-Lyttleton mass accretion rate applies (Proc. Camb. Phil. Soc., Math. Phys. Sci. 35: 405 (1939)) the accretion of interstellar matter by the Sun is sufficient to enhance the surface heavy element abundances. This will also apply to other solar-type stars. The enhancement may be sufficient to allow the construction of consistent solar models with an interior heavy element abundance significantly lower than the observed surface abundance. This state of affairs lowers the predicted solar neutrino flux. It has been suggested that a similar enhancement of surface abundances might occur due to accretion of 'planetesimals' left over after formation of the solar system, and both processes may occur, thereby increasing the effect. The simple accretion model of Hoyle and Lyttleton is discussed mathematically. A crucial question to be answered by future research, however, is whether or not accretion on to the solar surface actually occurs. One of the most obvious obstacles is the outward flowing solar wind, and this is discussed. It appears that the outward flow can be reversed to an inward flow for certain interstellar cloud densities. (U.K.)

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

    Science.gov (United States)

    Bhattacharyya, Sudip; Chakrabarty, Deepto

    2017-01-01

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

  1. Origin of chemically distinct discs in the Auriga cosmological simulations

    Science.gov (United States)

    Grand, Robert J. J.; Bustamante, Sebastián; Gómez, Facundo A.; Kawata, Daisuke; Marinacci, Federico; Pakmor, Rüdiger; Rix, Hans-Walter; Simpson, Christine M.; Sparre, Martin; Springel, Volker

    2018-03-01

    The stellar disc of the Milky Way shows complex spatial and abundance structure that is central to understanding the key physical mechanisms responsible for shaping our Galaxy. In this study, we use six very high resolution cosmological zoom-in simulations of Milky Way-sized haloes to study the prevalence and formation of chemically distinct disc components. We find that our simulations develop a clearly bimodal distribution in the [α/Fe]-[Fe/H] plane. We find two main pathways to creating this dichotomy, which operate in different regions of the galaxies: (a) an early (z > 1) and intense high-[α/Fe] star formation phase in the inner region (R ≲ 5 kpc) induced by gas-rich mergers, followed by more quiescent low-[α/Fe] star formation; and (b) an early phase of high-[α/Fe] star formation in the outer disc followed by a shrinking of the gas disc owing to a temporarily lowered gas accretion rate, after which disc growth resumes. In process (b), a double-peaked star formation history around the time and radius of disc shrinking accentuates the dichotomy. If the early star formation phase is prolonged (rather than short and intense), chemical evolution proceeds as per process (a) in the inner region, but the dichotomy is less clear. In the outer region, the dichotomy is only evident if the first intense phase of star formation covers a large enough radial range before disc shrinking occurs; otherwise, the outer disc consists of only low-[α/Fe] sequence stars. We discuss the implication that both processes occurred in the Milky Way.

  2. Optic disc oedema

    DEFF Research Database (Denmark)

    Nielsen, Marianne Kromann; Hamann, Steffen

    2014-01-01

    Optic disc oedema describes the nonspecific, localized swelling of the optic nerve head regardless of aetiology. Therefore, differentiating among the various aetiologies depends on a thorough history and knowledge of the clinical characteristics of the underlying conditions. Papilloedema strictly...... refers to optic disc oedema as a consequence of elevated intracranial pressure. It is usually a bilateral condition and visual function is preserved until late. Optic disc oedema caused by an anterior optic neuropathy is usually unilateral and accompanied by the loss of visual function....

  3. Dippers and dusty disc edges: new diagnostics and comparison to model predictions

    Science.gov (United States)

    Bodman, Eva H. L.; Quillen, Alice C.; Ansdell, Megan; Hippke, Michael; Boyajian, Tabetha S.; Mamajek, Eric E.; Blackman, Eric G.; Rizzuto, Aaron; Kastner, Joel H.

    2017-09-01

    We revisit the nature of large dips in flux from extinction by dusty circumstellar material that is observed by Kepler for many young stars in the Upper Sco and ρ Oph star formation regions. These young, low-mass 'dipper' stars are known to have low accretion rates and primarily host moderately evolved dusty circumstellar discs. Young low-mass stars often exhibit rotating starspots that cause quasi-periodic photometric variations. We found no evidence for periods associated with the dips that are different from the starspot rotation period in spectrograms constructed from the light curves. The material causing the dips in most of these light curves must be approximately corotating with the star. We find that disc temperatures computed at the disc corotation radius are cool enough that dust should not sublime. Crude estimates for stellar magnetic field strengths and accretion rates are consistent with magnetospheric truncation near the corotation radius. Magnetospheric truncation models can explain why the dips are associated with material near corotation and how dusty material is lifted out of the mid-plane to obscure the star that would account for the large fraction of young low-mass stars that are dippers. We propose that variations in disc orientation angle, stellar magnetic field dipole tilt axis and disc accretion rate are underlying parameters accounting for differences in the dipper light curves.

  4. Planetary accretion in circumstellar disks

    Science.gov (United States)

    Lissauer, Jack J.; Stewart, Glen R.

    1993-01-01

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

  5. Hot Accretion onto Black Holes with Outflow

    Science.gov (United States)

    Park, Myeong-Gu; Han, Du-Hwan

    2018-01-01

    Classic Bondi accretion flow can be generalized to rotating viscous accretion flow. Study of hot accretion flow onto black holes show that its physical charateristics change from Bondi-like for small gas angular momentum to disk-like for Keperian gas angular momentum. Especially, the mass accretion rate divided by the Bondi accretion rate is proportional to the viscosity parameter alpha and inversely proportional to the gas angular momentum divided by the Keplerian angular momentum at the Bondi radius for gas angular momentum comparable to the Keplerian value. The possible presence of outflow will increase the mass inflow rate at the Bondi radius but decrease the mass accretion rate across the black hole horizon by many orders of magnitude. This implies that the growth history of supermassive black holes and their coevolution with host galaxies will be dramatically changed when the accreted gas has angular momentum or develops an outflow.

  6. Hot Accretion onto Black Holes with Outflow

    Directory of Open Access Journals (Sweden)

    Park Myeong-Gu

    2018-01-01

    Full Text Available Classic Bondi accretion flow can be generalized to rotating viscous accretion flow. Study of hot accretion flow onto black holes show that its physical charateristics change from Bondi-like for small gas angular momentum to disk-like for Keperian gas angular momentum. Especially, the mass accretion rate divided by the Bondi accretion rate is proportional to the viscosity parameter alpha and inversely proportional to the gas angular momentum divided by the Keplerian angular momentum at the Bondi radius for gas angular momentum comparable to the Keplerian value. The possible presence of outflow will increase the mass inflow rate at the Bondi radius but decrease the mass accretion rate across the black hole horizon by many orders of magnitude. This implies that the growth history of supermassive black holes and their coevolution with host galaxies will be dramatically changed when the accreted gas has angular momentum or develops an outflow.

  7. On total disc replacement.

    Science.gov (United States)

    Berg, Svante

    2011-02-01

    Low back pain consumes a large part of the community's resources dedicated to health care and sick leave. Back disorders also negatively affect the individual leading to pain suffering, decreased quality-of-life and disability. Chronic low back pain (CLBP) due to degenerative disc disease (DDD) is today often treated with fusion when conservative treatment has failed and symptoms are severe. This treatment is as successful as arthroplasty is for hip arthritis in restoring the patient's quality of life and reducing disability. Even so, there are some problems with this treatment, one of these being recurrent CLBP from an adjacent segment (ASD) after primarily successful surgery. This has led to the development of alternative surgical treatments and devices that maintain or restore mobility, in order to reduce the risk for ASD. Of these new devices, the most frequently used are the disc prostheses used in Total Disc Replacement (TDR). This thesis is based on four studies comparing total disc replacement with posterior fusion. The studies are all based on a material of 152 patients with DDD in one or two segments, aged 20-55 years that were randomly treated with either posterior fusion or TDR. The first study concerned clinical outcome and complications. Follow-up was 100% at both one and two years. It revealed that both treatment groups had a clear benefit from treatment and that patients with TDR were better in almost all outcome scores at one-year follow-up. Fusion patients continued to improve during the second year. At two-year follow-up there was a remaining difference in favour of TDR for back pain. 73% in the TDR group and 63% in the fusion group were much better or totally pain-free (n.s.), while twice as many patients in the TDR group were totally pain free (30%) compared to the fusion group (15%). Time of surgery and total time in hospital were shorter in the TDR group. There was no difference in complications and reoperations, except that seventeen of the

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

    Science.gov (United States)

    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

  9. Correlating non-linear properties with spectral states of RXTE data: possible observational evidences for four different accretion modes around compact objects

    Science.gov (United States)

    Adegoke, Oluwashina; Dhang, Prasun; Mukhopadhyay, Banibrata; Ramadevi, M. C.; Bhattacharya, Debbijoy

    2018-05-01

    By analysing the time series of RXTE/PCA data, the non-linear variabilities of compact sources have been repeatedly established. Depending on the variation in temporal classes, compact sources exhibit different non-linear features. Sometimes they show low correlation/fractal dimension, but in other classes or intervals of time they exhibit stochastic nature. This could be because the accretion flow around a compact object is a non-linear general relativistic system involving magnetohydrodynamics. However, the more conventional way of addressing a compact source is the analysis of its spectral state. Therefore, the question arises: What is the connection of non-linearity to the underlying spectral properties of the flow when the non-linear properties are related to the associated transport mechanisms describing the geometry of the flow? This work is aimed at addressing this question. Based on the connection between observed spectral and non-linear (time series) properties of two X-ray binaries: GRS 1915+105 and Sco X-1, we attempt to diagnose the underlying accretion modes of the sources in terms of known accretion classes, namely, Keplerian disc, slim disc, advection dominated accretion flow and general advective accretion flow. We explore the possible transition of the sources from one accretion mode to others with time. We further argue that the accretion rate must play an important role in transition between these modes.

  10. 'Hard discs' associated with lumbar disc herniation: CT analysis

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Il Kwon; Bang, Dae Hong; Yim, Jung Ik; Lee, Jae Mun; Bahk, Yong Whee [Catholic University Medical College, Seoul (Korea, Republic of)

    1989-02-15

    Thirty cases showing hard discs were collected from 206 consecutive cases of posterior disk herniation during the past one and a half years period. According to the shape of hard disk and the presence of marginal bone defect (MBD) of vertebral end plate, 30 cases could be categorized into 4 distinct groups. They were small hard disc with focal MBD (group 1), large hard disc with broad based MBD (group 2), hard disc separated from vertebral body without MBD (group 3) and hard disc fused with vertebral body without MBD (group 4). There were 14 patients in group 1. In all but one case, the hard disc and MBDs were located at the paramedial aspect of the posterior margin of the end plate. Ten (76.9%) of these had Schmorl's nodes and these were considered to represented an avulsion from the weakened bone margin as the disk herniated acutely. The posterior longitudinal ligament seemed to have prevented detachment of the bony fragment. Group 2 included 2 patients and CT findings as well as plain X-ray features were identical to a limbus vertebra. This was considered to represent passive displacement of bony fragment by the intravertebral herniation of the disk. Nine patients belonged to group 3 and represent dystrophic calcifications of herniated disk. Group 4 included 5 patients and was disclosed as a simple osteophyte. From our study, it was concluded; (1) that the hard disc seen in lumbar CT scan was probably the results of the detachment of a bone fragment from the vertebral end plate which has an underlying weak area due to the herniated disc as well as a calcification or osteophyte formation and (2) specific terms (avulsed fragment, limbus vertebra, calcification or spur formation) is more preferable to use than hard disc which is inaccurate.

  11. Expression of heparanase isoforms in intervertebral discs classified according to Pfirrmann grading system for disc degeneration.

    Science.gov (United States)

    Rodrigues, Luciano Miller Reis; Oliveira, Lilian Zerbinatti de; Pinhal, Maria Aparecida da Silva

    2013-06-01

    This is a quantitative study of heparanase isoforms expression in degenerative and nondegenerative intervertebral discs (IVDs). To quantify the expression of both heparanase isoforms (HPSE1 and HPSE2) in IVD tissues as classified by different degeneration grades using the Pfirrmann grading system, and to correlate the expression with the loss of extracellular matrix molecules observed in patients with the disease. The loss of proteoglycans as observed in IVD degeneration may occur due to the enhanced expression of matrix degrading enzymes, such as heparanase. However, the heparanase function in IVD degeneration remains unclear. This study comprised 53 surgical samples of degenerative discs obtained from patients with lumbar disc degeneration and 12 control samples collected from healthy individuals without any degenerative lumbar disc alterations who had accidental spine fractures.All patients underwent magnetic resonance imaging based on the Pfirrmann grading system for disc degeneration. Only the specimens that were classified according to magnetic resonance imaging evaluations as Pfirrmann grades I, II, III, and IV were analyzed.The tissue sections of the disc samples were subject to immunohistochemical staining with antibodies against the heparanase isoforms and to quantitative real time PCR to amplify heparanase isoforms cDNA. Protein and mRNA expressions were quantified. Analysis of variance and Student t test were used to compare the means of the study populations. The data demonstrated a gradual increase in both the heparanase isoform protein expression and disc degeneration progression. Besides, mRNA expression of both heparanase isoforms were significantly higher in degenerative than nondegenerative IVDs. The overexpression of HPSE1 and HPSE2 in the intervertebral degenerated discs suggests a role for these factors in mediating extracellular matrix remodeling in degenerative discs during disease development.

  12. The Physical Relation between Disc and Coronal Emission in Quasars

    Directory of Open Access Journals (Sweden)

    Elisabeta Lusso

    2018-01-01

    Full Text Available We propose a modified version of the observed non-linear relation between the X-ray (2 keV and the ultraviolet (2,500 Å emission in quasars (i.e., LX∝LUVγ which involves the full width at half-maximum, FWHM, of the broad emission line, i.e., LX∝LUVγ^ FWHMβ^. By analyzing a sample of 550 optically selected non-jetted quasars in the redshift range of 0.36–2.23 from the Sloan Digital Sky Survey cross matched with the XMM-Newton catalog 3XMM-DR6, we found that the additional dependence of the observed LX − LUV correlation on the FWHM of the Mgii broad emission line is statistically significant. Our statistical analysis leads to a much tighter relation with respect to the one neglecting FWHM, and it does not evolve with redshift. We interpret this new relation within an accretion disc corona scenario where reconnection and magnetic loops above the accretion disc can account for the production of the primary X-ray radiation. For a broad line region size depending on the disc luminosity as Rblr∝Ldisc0.5, we find that LX∝LUV4/7 FWHM4/7, which is in very good agreement with the observed correlation.

  13. Probing the Accretion Processes in Soft X-Ray Selected Polars

    Directory of Open Access Journals (Sweden)

    I. Traulsen

    2015-02-01

    Full Text Available High-energy data of accreting white dwarfs give access to the regime of the primary accretion-induced energy release and the different proposed accretion scenarios. We perform XMM-Newton observations of polars selected due to their ROSAT hardness ratios close to -1.0 and model the emission processes in accretion column and accretion region. Our models consider the multi-temperature structure of the emission regions and are mainly determined by mass-flow density, magnetic field strength, and white-dwarf mass. To describe the full spectral energy distribution from infrared to X-rays in a physically consistent way, we include the stellar contributions and establish composite models, which will also be of relevance for future X-ray missions. We confirm the X-ray soft nature of three polars.

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

    Science.gov (United States)

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

    2004-01-01

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

  15. Notochord Cells in Intervertebral Disc Development and Degeneration

    Directory of Open Access Journals (Sweden)

    Matthew R. McCann

    2016-01-01

    Full Text Available The intervertebral disc is a complex structure responsible for flexibility, multi-axial motion, and load transmission throughout the spine. Importantly, degeneration of the intervertebral disc is thought to be an initiating factor for back pain. Due to a lack of understanding of the pathways that govern disc degeneration, there are currently no disease-modifying treatments to delay or prevent degenerative disc disease. This review presents an overview of our current understanding of the developmental processes that regulate intervertebral disc formation, with particular emphasis on the role of the notochord and notochord-derived cells in disc homeostasis and how their loss can result in degeneration. We then describe the role of small animal models in understanding the development of the disc and their use to interrogate disc degeneration and associated pathologies. Finally, we highlight essential development pathways that are associated with disc degeneration and/or implicated in the reparative response of the tissue that might serve as targets for future therapeutic approaches.

  16. Pseudoenhancement of intervertebral disc herniation

    Energy Technology Data Exchange (ETDEWEB)

    Araki, Y.; Ootani, M.; Furukawa, T.; Tsukaguchi, I. (Dept. of Radiology, Osaka Rosai Hospital (Japan)); Mitomo, M. (Dept. of Radiology, Osaka Univ. Medical School (Japan))

    1992-08-01

    Two patients with intervertebral disc herniation appeared to demonstrate abnormally diffuse and intense enhancement of the disc after intravenous administration of gadolinium-DTPA for MRI. Surgery disclosed a dilated epidural venous plexus in one and vascular granulation tissue in the other, associated with the herniated disc material. The mechanism of this 'pseudoenhancement' of the disc appears to be a partial volume effect of disc material and the adjacent veins or granulation tissue. Pseudoenhancement of a herniated disc should be included in the differential diagnosis of a diffusely enhancing epidural mass. (orig.).

  17. Protostellar accretion traced with chemistry

    DEFF Research Database (Denmark)

    Frimann, Søren; Jørgensen, Jes Kristian; Padoan, Paolo

    2016-01-01

    used foranalysing the observations. Methods: Simple freeze-out andsublimation chemistry is added to the simulation, and syntheticC18O line cubes are created for a large number of simulatedprotostars. The spatial extent of C18O is measured for thesimulated protostars and compared directly to a sample......% of the protostars in the simulation show extendedC18O emission, as opposed to approximately 50% in theobservations, indicating that the magnitude and frequency of episodicaccretion events in the simulation is too low relative to observations.The protostellar accretion rates in the simulation are primarilymodulated...

  18. Theory of Disk Accretion onto Magnetic Stars

    Directory of Open Access Journals (Sweden)

    Lai Dong

    2014-01-01

    Full Text Available Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields, white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron star and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.

  19. Active galactic nucleus outflows in galaxy discs

    Science.gov (United States)

    Hartwig, Tilman; Volonteri, Marta; Dashyan, Gohar

    2018-05-01

    Galactic outflows, driven by active galactic nuclei (AGNs), play a crucial role in galaxy formation and in the self-regulated growth of supermassive black holes (BHs). AGN feedback couples to and affects gas, rather than stars, and in many, if not most, gas-rich galaxies cold gas is rotationally supported and settles in a disc. We present a 2D analytical model for AGN-driven outflows in a gaseous disc and demonstrate the main improvements, compared to existing 1D solutions. We find significant differences for the outflow dynamics and wind efficiency. The outflow is energy-driven due to inefficient cooling up to a certain AGN luminosity (˜1043 erg s-1 in our fiducial model), above which the outflow remains momentum-driven in the disc up to galactic scales. We reproduce results of 3D simulations that gas is preferentially ejected perpendicular to the disc and find that the fraction of ejected interstellar medium is lower than in 1D models. The recovery time of gas in the disc, defined as the free-fall time from the radius to which the AGN pushes the ISM at most, is remarkably short, of the order 1 Myr. This indicates that AGN-driven winds cannot suppress BH growth for long. Without the inclusion of supernova feedback, we find a scaling of the BH mass with the halo velocity dispersion of MBH ∝ σ4.8.

  20. Footprint mismatch in lumbar total disc arthroplasty.

    Science.gov (United States)

    Gstoettner, Michaela; Michaela, Gstoettner; Heider, Denise; Denise, Heider; Liebensteiner, Michael; Bach, Christian Michael; Michael, Bach Christian

    2008-11-01

    Lumbar disc arthroplasty has become a popular modality for the treatment of degenerative disc disease. The dimensions of the implants are based on early published geometrical measurements of vertebrae; the majority of these were cadaver studies. The fit of the prosthesis in the intervertebral space is of utmost importance. An undersized implant may lead to subsidence, loosening and biomechanical failure due to an incorrect center of rotation. The aim of the present study was to measure the dimensions of lumbar vertebrae based on CT scans and assess the accuracy of match in currently available lumbar disc prostheses. A total of 240 endplates of 120 vertebrae were included in the study. The sagittal and mediolateral diameter of the upper and lower endplates were measured using a digital measuring system. For the levels L4/L5 and L5/S1, an inappropriate size match was noted in 98.8% (Prodisc L) and 97.6% (Charite) with regard to the anteroposterior diameter. Mismatch in the anterior mediolateral diameter was noted in 79.3% (Prodisc L) and 51.2% (Charite) while mismatch in the posterior mediolateral diameter was observed in 91.5% (Prodisc L) and 78% (Charite) of the endplates. Surgeons and manufacturers should be aware of the size mismatch of currently available lumbar disc prostheses, which may endanger the safety and efficacy of the procedure. Larger footprints of currently available total disc arthroplasties are required.

  1. Local expansions and accretive mappings

    Directory of Open Access Journals (Sweden)

    W. A. Kirk

    1983-01-01

    Full Text Available Let X and Y be complete metric spaces with Y metrically convex, let D⊂X be open, fix u0∈X, and let d(u=d(u0,u for all u∈D. Let f:X→2Y be a closed mapping which maps open subsets of D onto open sets in Y, and suppose f is locally expansive on D in the sense that there exists a continuous nonincreasing function c:R+→R+ with ∫+∞c(sds=+∞ such that each point x∈D has a neighborhood N for which dist(f(u,f(v≥c(max{d(u,d(v}d(u,v for all u,v∈N. Then, given y∈Y, it is shown that y∈f(D iff there exists x0∈D such that for x∈X\\D, dist(y,f(x0≤dist(u,f(x. This result is then applied to the study of existence of zeros of (set-valued locally strongly accretive and ϕ-accretive mappings in Banach spaces

  2. Cervical intervertebral disc replacement.

    Science.gov (United States)

    Cason, Garrick W; Herkowitz, Harry N

    2013-02-06

    Symptomatic adjacent-level disease after cervical fusion has led to the development and testing of several disc-replacement prostheses. Randomized controlled trials of cervical disc replacement (CDR) compared with anterior cervical discectomy and fusion (ACDF) have demonstrated at least equivalent clinical results for CDR with similar or lower complication rates. Biomechanical, kinematic, and radiographic studies of CDR reveal that the surgical level and adjacent vertebral level motion and center of rotation more closely mimic the native state. Lower intradiscal pressures adjacent to CDR may help decrease the incidence of adjacent spinal-level disease, but long-term follow-up is necessary to evaluate this theory.

  3. Isolated Optic Disc Tuberculosis

    Science.gov (United States)

    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. Isolated Optic Disc Tuberculosis

    Directory of Open Access Journals (Sweden)

    Ahmad M. Mansour

    2015-09-01

    Full Text Available 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.

  5. Hydromagnetic stability of a slim disc in a stationary geometry

    Science.gov (United States)

    Araya-Góchez, Rafael Angel

    2002-12-01

    The magnetorotational instability originates from the elastic coupling of fluid elements in orbit around a gravitational well. Since inertial accelerations play a fundamental dynamical role in the process, one may expect substantial modifications by strong gravity in the case of accretion on to a black hole. In this paper, we develop a fully covariant, Lagrangian displacement vector field formalism with the aim of addressing these issues for a disc embedded in a stationary geometry with negligible radial flow. This construction enables a transparent connection between particle dynamics and the ensuing dispersion relation for magnetohydrodynamic wave modes. The magnetorotational instability (MRI) - in its incompressible variant - is found to operate virtually unabated down to the marginally stable orbit; the putative inner boundary of standard accretion disc theory. To obtain a qualitative feel for the dynamical evolution of the flow below rms, we assume a mildly advective accretion flow such that the angular velocity profile departs slowly from circular geodesic flow. This exercise suggests that turbulent eddies will occur at spatial scales approaching the radial distance while tracking the surfaces of null angular velocity gradients. The implied field topology, namely large-scale horizontal field domains, should yield strong mass segregation at the displacement nodes of the non-linear modes when radiation stress dominates the local disc structure (an expectation supported by quasi-linear arguments and by the non-linear behaviour of the MRI in a non-relativistic setting). Under this circumstance, baryon-poor flux in horizontal field domains will be subject to radial buoyancy and to the Parker instability, thereby promoting the growth of poloidal field.

  6. Studies of accreting and non-accreting neutron stars

    International Nuclear Information System (INIS)

    Stollman, G.M.

    1987-01-01

    This thesis is divided into three parts. Part A is devoted to the statistical study of radio pulsars, in which the observations of nearly all known pulsars are used to study their properties such as magnetic field strengths, rotation periods, space velocities as well as their evolution in time. Part B is devoted to the modelling and understanding of quasi-periodic oscillations (QPO) in low-mass X-ray binaries. But, this study is mainly concerned with the accretion process in these sources, and one may hope to learn more about the neutron stars in these systems when the understanding of QPO is improved. In Part C the problem of 'super-Eddington luminosities' in X-ray burst sources is treated. The idea is that a good understanding of the burst process, which takes place directly at the surface of the neutron star, will eventually improve our understanding of the neutron stars themselves. (Auth.)

  7. Investigation of Product Performance of Al-Metal Matrix Composites Brake Disc using Finite Element Analysis

    International Nuclear Information System (INIS)

    Fatchurrohman, N; Marini, C D; Suraya, S; Iqbal, AKM Asif

    2016-01-01

    The increasing demand of fuel efficiency and light weight components in automobile sectors have led to the development of advanced material parts with improved performance. A specific class of MMCs which has gained a lot of attention due to its potential is aluminium metal matrix composites (Al-MMCs). Product performance investigation of Al- MMCs is presented in this article, where an Al-MMCs brake disc is analyzed using finite element analysis. The objective is to identify the potentiality of replacing the conventional iron brake disc with Al-MMCs brake disc. The simulation results suggested that the MMCs brake disc provided better thermal and mechanical performance as compared to the conventional cast iron brake disc. Although, the Al-MMCs brake disc dissipated higher maximum temperature compared to cast iron brake disc's maximum temperature. The Al-MMCs brake disc showed a well distributed temperature than the cast iron brake disc. The high temperature developed at the ring of the disc and heat was dissipated in circumferential direction. Moreover, better thermal dissipation and conduction at brake disc rotor surface played a major influence on the stress. As a comparison, the maximum stress and strain of Al-MMCs brake disc was lower than that induced on the cast iron brake disc. (paper)

  8. Rotation and Accretion Powered Pulsars

    Energy Technology Data Exchange (ETDEWEB)

    Kaspi, V M [Department of Physics, McGill University, 3600 University St, Montreal, QC H3A 2T8 (Canada)

    2008-03-07

    Pulsar astrophysics has come a long way in the 40 years since the discovery of the first pulsar by Bell and Hewish. From humble beginnings as bits of 'scruff' on the Cambridge University group's chart recorder paper, the field of pulsars has blossomed into a major area of mainstream astrophysics, with an unparalleled diversity of astrophysical applications. These range from Nobel-celebrated testing of general relativity in the strong-field regime to constraining the equation-of-state of ultradense matter; from probing the winds of massive stars to globular cluster evolution. Previous notable books on the subject of pulsars have tended to focus on some particular topic in the field. The classic text Pulsars by Manchester and Taylor (1977 San Francisco, CA: Freeman) targeted almost exclusively rotation-powered radio pulsars, while the Meszaros book High-Energy Radiation from Magnetized Neutron Stars (1992 Chicago, IL: University of Chicago Press) considered both rotation- and accretion-powered neutron stars, but focused on their radiation at x-ray energies and above. The recent book Neutron Stars 1 by Haensel et al (2007 Berlin: Springer) considers only the equation of state and neutron-star structure. Into this context appears Rotation and Accretion Powered Pulsars, by Pranab Ghosh. In contrast to other books, here the author takes an encyclopedic approach and attempts to synthesize practically all of the major aspects of the two main types of neutron star. This is ambitious. The only comparable undertaking is the useful but more elementary Lyne and Graham-Smith text Pulsar Astronomy (1998 Cambridge: Cambridge University Press), or Compact Stellar X-ray Sources (eds Lewin and van der Klis, 2006 Cambridge: Cambridge University Press), an anthology of technical review articles that also includes black hole topics. Rotation and Accretion Powered Pulsars thus fills a clear void in the field, providing a readable, graduate-level book that covers nearly

  9. MN Lup: X-RAYS FROM A WEAKLY ACCRETING T TAURI STAR

    Energy Technology Data Exchange (ETDEWEB)

    Guenther, H. M.; Wolk, S. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Wolter, U.; Robrade, J., E-mail: hguenther@cfa.harvard.edu [Universitaet Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg (Germany)

    2013-07-01

    Young T Tauri stars (TTS) are surrounded by an accretion disk, which over time disperses due to photoevaporation, accretion, and possibly planet formation. The accretion shock on the central star produces an UV/optical veiling continuum, line emission, and X-ray signatures. As the accretion rate decreases, the impact on the central star must change. In this article we study MN Lup, a young star where no indications of a disk are seen in IR observations. We present XMM-Newton and VLT/UVES observations, some of them taken simultaneously. The X-ray data show that MN Lup is an active star with L{sub X} /L{sub bol} close to the saturation limit. However, we find high densities (n{sub e} > 3 Multiplication-Sign 10{sup 10} cm{sup -3}) in the X-ray grating spectrum. This can be well fitted using an accretion shock model with an accretion rate of 2 Multiplication-Sign 10{sup -11} M{sub Sun} yr{sup -1}. Despite the simple H{alpha} line profile which has a broad component, but no absorption signatures as typically seen on accreting TTS, we find rotational modulation in Ca II K and in photospheric absorption lines. These line profile modulations do not clearly indicate the presence of a localized hot accretion spot on the star. In the H{alpha} line we see a prominence in absorption about 2R{sub *} above the stellar surface-the first of its kind on a TTS. MN Lup is also the only TTS where accretion is seen, but no dust disk is detected that could fuel it. We suggest that MN Lup presents a unique and short-lived state in the disk evolution. It may have lost its dust disk only recently and is now accreting the remaining gas at a very low rate.

  10. ACCRETION AND MAGNETIC RECONNECTION IN THE CLASSICAL T TAURI BINARY DQ TAU

    Energy Technology Data Exchange (ETDEWEB)

    Tofflemire, Benjamin M.; Mathieu, Robert D. [Department of Astronomy, University of Wisconsin–Madison, 475 North Charter Street, Madison, WI 53706 (United States); Ardila, David R. [The Aerospace Corporation, M2-266, El Segundo, CA 90245 (United States); Akeson, Rachel L.; Ciardi, David R. [NASA Exoplanet Science Institute, IPAC/Caltech, Pasadena, CA 91125 (United States); Johns-Krull, Christopher [Department of Physics and Astronomy, Rice University, Houston, TX 77005 (United States); Herczeg, Gregory J. [The Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Quijano-Vodniza, Alberto [University of Nariño Observatory, Pasto, Nariño (Colombia)

    2017-01-20

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

  11. Low density, radiatively inefficient rotating-accretion flow onto a black hole

    Science.gov (United States)

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

    2018-02-01

    We study low-density axisymmetric accretion flows onto black holes (BHs) with two-dimensional hydrodynamical simulations, adopting the α-viscosity prescription. When the gas angular momentum is low enough to form a rotationally supported disk within the Bondi radius (RB), we find a global steady accretion solution. The solution consists of a rotational equilibrium distribution around r ˜ RB, where the density follows ρ∝(1 + RB/r)3/2, surrounding a geometrically thick and optically thin accretion disk at the centrifugal radius RC( energy generated by viscosity is transported via convection. Physical properties of the inner solution agree with those expected in convection-dominated accretion flows (CDAF; ρ∝r-1/2). In the inner solution, the gas inflow rate decreases towards the center due to convection (\\dot{M}∝ r), and the net accretion rate (including both inflows and outflows) is strongly suppressed by several orders of magnitude from the Bondi accretion rate \\dot{M}_B. The net accretion rate depends on the viscous strength, following \\dot{M}/\\dot{M}_B∝ (α /0.01)^{0.6}. This solution holds for low accretion rates of \\dot{M}_B/\\dot{M}_Edd≲ 10^{-3} having minimal radiation cooling, where \\dot{M}_Edd is the Eddington accretion rate. In a hot plasma at the bottom (r energy flux. Since suppression of the accretion by convection ceases, the final BH feeding rate is found to be \\dot{M}/\\dot{M}_B˜ 10^{-3}-10^{-2}. This rate is as low as \\dot{M}/\\dot{M}_Edd˜ 10^{-7}-10^{-6} inferred for SgrA* and the nuclear BHs in M31 and M87, and can explain their low luminosities, without invoking any feedback mechanism.

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

    Science.gov (United States)

    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.

  13. Tracing Planets in Circumstellar Discs

    Directory of Open Access Journals (Sweden)

    Uribe Ana L.

    2013-04-01

    Full Text Available Planets are assumed to form in circumstellar discs around young stellar objects. The additional gravitational potential of a planet perturbs the disc and leads to characteristic structures, i.e. spiral waves and gaps, in the disc density profile. We perform a large-scale parameter study on the observability of these planet-induced structures in circumstellar discs in the (submm wavelength range for the Atacama Large (SubMillimeter Array (ALMA. On the basis of hydrodynamical and magneto-hydrodynamical simulations of star-disc-planet models we calculate the disc temperature structure and (submm images of these systems. These are used to derive simulated ALMA maps. Because appropriate objects are frequent in the Taurus-Auriga region, we focus on a distance of 140 pc and a declination of ≈ 20°. The explored range of star-disc-planet configurations consists of six hydrodynamical simulations (including magnetic fields and different planet masses, nine disc sizes with outer radii ranging from 9 AU to 225 AU, 15 total disc masses in the range between 2.67·10-7 M⊙ and 4.10·10-2 M⊙, six different central stars and two different grain size distributions, resulting in 10 000 disc models. At almost all scales and in particular down to a scale of a few AU, ALMA is able to trace disc structures induced by planet-disc interaction or the influence of magnetic fields in the wavelength range between 0.4...2.0 mm. In most cases, the optimum angular resolution is limited by the sensitivity of ALMA. However, within the range of typical masses of protoplane tary discs (0.1 M⊙...0.001 M⊙ the disc mass has a minor impact on the observability. At the distance of 140 pc it is possible to resolve discs down to 2.67·10-6 M⊙ and trace gaps in discs with 2.67·10-4 M⊙ with a signal-to-noise ratio greater than three. In general, it is more likely to trace planet-induced gaps in magneto-hydrodynamical disc models, because gaps are wider in the presence of

  14. The angular momentum of hot coronae around spiral galaxies and its impact on the evolution of star forming discs

    NARCIS (Netherlands)

    Pezzulli, G.; Fraternali, F.; Binney, J.

    Galaxy formation theory and recent observations indicate that spiral galaxies are surrounded by massive and hot coronae, which potentially constitute a huge source of mass and angular momentum for the star forming discs embedded within them. Accretion from these reservoirs is likely a key ingredient

  15. Two-dimensional models of layered protoplanetary discs. II. - The effect of a residual viscosity in the dead zone

    Czech Academy of Sciences Publication Activity Database

    Wünsch, Richard; Gawryszczak, A.; Klahr, H.; Rózycka, M.

    2006-01-01

    Roč. 367, č. 2 (2006), s. 773-780 ISSN 0035-8711 R&D Projects: GA AV ČR IAB3003106 Institutional research plan: CEZ:AV0Z10030501 Keywords : accretion discs * hydrodynamics * instabilities Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.057, year: 2006

  16. The DISC Quotient

    Science.gov (United States)

    Elliott, John R.; Baxter, Stephen

    2012-09-01

    D.I.S.C: Decipherment Impact of a Signal's Content. The authors present a numerical method to characterise the significance of the receipt of a complex and potentially decipherable signal from extraterrestrial intelligence (ETI). The purpose of the scale is to facilitate the public communication of work on any such claimed signal, as such work proceeds, and to assist in its discussion and interpretation. Building on a "position" paper rationale, this paper looks at the DISC quotient proposed and develops the algorithmic steps and comprising measures that form this post detection strategy for information dissemination, based on prior work on message detection, decipherment. As argued, we require a robust and incremental strategy, to disseminate timely, accurate and meaningful information, to the scientific community and the general public, in the event we receive an "alien" signal that displays decipherable information. This post-detection strategy is to serve as a stepwise algorithm for a logical approach to information extraction and a vehicle for sequential information dissemination, to manage societal impact. The "DISC Quotient", which is based on signal analysis processing stages, includes factors based on the signal's data quantity, structure, affinity to known human languages, and likely decipherment times. Comparisons with human and other phenomena are included as a guide to assessing likely societal impact. It is submitted that the development, refinement and implementation of DISC as an integral strategy, during the complex processes involved in post detection and decipherment, is essential if we wish to minimize disruption and optimize dissemination.

  17. Optic disc drusen

    DEFF Research Database (Denmark)

    Fledelius, Hans C

    2017-01-01

    , which, in view of the small disc at risk, may seem a paradox. METHODS: This is an observational retrospective study on an eye clinic series (n = 49), focusing on visual acuity, kinetic/static perimetry, and longitudinal trends, to include the question of eventual visual incapacity. RESULTS: Forty...

  18. Biomechanical and biochemical outcomes of porcine temporomandibular joint disc deformation.

    Science.gov (United States)

    Matuska, Andrea M; Muller, Stephen; Dolwick, M Franklin; McFetridge, Peter S

    2016-04-01

    The structure-function relationship in the healthy temporomandibular joint (TMJ) disc has been well established, however the changes in dysfunctional joints has yet to be systematically evaluated. Due to the poor understanding of the etiology of temporomandibular disorders (TMDs) this study evaluated naturally occurring degenerative remodeling in aged female porcine temporomandibular joint (TMJ) discs in order to gain insight into the progression and effects on possible treatment strategies of TMDs. Surface and regional biomechanical and biochemical properties of discal tissues were determined in grossly deformed (≥Wilkes Stage 3) and morphologically normal (≤Wilkes Stage 2) TMJ discs. Compared to normal disc structure the deformed discs lacked a smooth biconcave shape and characteristic ECM organization. Reduction in tensile biomechanical integrity and increased compressive stiffness and cellularity was found in deformed discs. Regionally, the posterior and intermediate zones of the disc were most frequently affected along with the inferior surface. The frequency of degeneration observed on the inferior surface of the disc (predominantly posterior), suggests that a disruption in the disc-condyle relationship likely contributes to the progression of joint dysfunction more than the temporodiscal relationship. As such, the inferior joint space may be an important consideration in early clinical diagnosis and treatment of TMDs, as it is overlooked in techniques performed in the upper joint space, including arthroscopy and arthrocentesis. Furthermore, permanent damage to the disc mechanical properties would limit the ability to successfully reposition deformed discs, highlighting the importance of emerging therapies such as tissue engineering. Copyright © 2016 Elsevier Ltd. All rights reserved.

  19. Mixed ice accretion on aircraft wings

    Science.gov (United States)

    Janjua, Zaid A.; Turnbull, Barbara; Hibberd, Stephen; Choi, Kwing-So

    2018-02-01

    Ice accretion is a problematic natural phenomenon that affects a wide range of engineering applications including power cables, radio masts, and wind turbines. Accretion on aircraft wings occurs when supercooled water droplets freeze instantaneously on impact to form rime ice or runback as water along the wing to form glaze ice. Most models to date have ignored the accretion of mixed ice, which is a combination of rime and glaze. A parameter we term the "freezing fraction" is defined as the fraction of a supercooled droplet that freezes on impact with the top surface of the accretion ice to explore the concept of mixed ice accretion. Additionally we consider different "packing densities" of rime ice, mimicking the different bulk rime densities observed in nature. Ice accretion is considered in four stages: rime, primary mixed, secondary mixed, and glaze ice. Predictions match with existing models and experimental data in the limiting rime and glaze cases. The mixed ice formulation however provides additional insight into the composition of the overall ice structure, which ultimately influences adhesion and ice thickness, and shows that for similar atmospheric parameter ranges, this simple mixed ice description leads to very different accretion rates. A simple one-dimensional energy balance was solved to show how this freezing fraction parameter increases with decrease in atmospheric temperature, with lower freezing fraction promoting glaze ice accretion.

  20. Foundations of Black Hole Accretion Disk Theory.

    Science.gov (United States)

    Abramowicz, Marek A; Fragile, P Chris

    2013-01-01

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

  1. Preliminary probabilistic prediction of ice/snow accretion on stay cables based on meteorological variables

    DEFF Research Database (Denmark)

    Roldsgaard, Joan Hee; Kiremidjian, A.; Georgakis, Christos T.

    The scope of the present paper is to present a framework for assessment of the probability of occurrence of ice/snow accretion on bridge cables. The framework utilizes Bayesian Probabilistic Networks and the methodology is illustrated with an example of the cable-stayed Øresund Bridge. The case...... study focuses on the ice/snow accretion due to the in-cloud icing or precipitation icing mechanisms and includes probabilistic assessments of the meteorological variables influencing the ice/snow accretion on the stay cables. Different probability distribution functions are utilized...

  2. Effect of rapid mass accretion onto the low-mass main sequence stars

    International Nuclear Information System (INIS)

    Sarna, M.J.; Ziolkowski, J.

    1988-01-01

    We investigated the effects of rapid mass accretion on low-mass main sequence stars with deep convective envelopes (0.3 and 0.5 M sun ), taking into account the heating of their photospheres by the kinetic energy of the infalling matter. We found that these stars develop highly inhomogeneous structure consisting of an interior formed by an almost unperturbed original star and the radiative envelope composed of the accreted matter. These two regions are separated by a very stable temperature inversion layer. Due to such structure accreting convective star may substantially increase its radius (contrary to earlier suggestions). 7 refs., 10 figs., 1 tab. (author)

  3. Accretion Processes in Star Formation

    DEFF Research Database (Denmark)

    Küffmeier, Michael

    Stars and their corresponding protoplanetary disks form in different environments of Giant Molecular Clouds. By carrying state-of-the art zoom-simulations with the magnetohydrodynamical code ramses, I investigated the accretion process around young stars that are embedded in such different...... environments. Starting from a turbulent (40 pc) 3 Giant Molecular cloud, efficient use of Adaptive Mesh Refinement technique allowed to resolve the processes inside of protoplanetary disks with grid sizes down to 0.06 AU, thus covering a range of spatial scales of more than six orders of magnitude. Accounting...... abundance in different types of the oldest solids of the Solar System (Calcium Aluminum rich inclusions) is not a result of early supernova injections. Instead, our results suggest thermal processing of dust grains as a likely scenario for the measured differences. Furthermore, the simulations show...

  4. Confrontation of the Magnetically Arrested Disc Scenario with Observations of FR II Sources

    Energy Technology Data Exchange (ETDEWEB)

    Rusinek, Katarzyna; Sikora, Marek, E-mail: krusinek@camk.edu.pl [Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw (Poland)

    2017-10-12

    The main aim of our work was to check whether powers of jets in FR II radio galaxies (RGs) and quasars (QSOs) can be reproduced by the Magnetically Arrested Disc (MAD) scenario. Assuming that established in the recent numerical simulations of the MAD scenario the (H/R){sup 2} dependence of the jet production efficiency is correct, we demonstrate that in order to reproduce the observed jet powers in FR II sources: (i) accretion discs must be geometrically much thicker than the standard ones; (ii) and/or that the jet production is strongly modulated.

  5. On the structure of circumbinary accretion disks and the tidal evolution of commensurable satellites

    International Nuclear Information System (INIS)

    Lin, D.N.C.; Papaloizou, J.

    1979-01-01

    The investigation is continued of tidal torques on accretion disk flows in the vicinity of close binary systems. It is shown that the tidal effect can truncate the inner edge of circumbinary accretion discs. If the viscous dissipation is weak in such disks, density enhancement can be produced at the outer Lindblad resonance. The results are applied to contact binaries and the formation of commensurable satellites in the solar system. In order to determine whether the present configurations are a result of formation, or subsequent tidal evolution, the forced eccentricity of resonant satellites is related to the Q values of the planet and satellites. It is found that while the Galilean satellites may owe their present configuration, in part, to tidal effects, this is unlikely for other commensurable pairs. (author)

  6. Accretion of Jupiter-mass planets in the limit of vanishing viscosity

    Energy Technology Data Exchange (ETDEWEB)

    Szulágyi, J.; Morbidelli, A.; Crida, A. [University of Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d' Azur, Laboratoire Lagrange, F-06304, Nice (France); Masset, F., E-mail: jszulagyi@oca.eu [Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, P.O. Box 48-3, 62251 Cuernavaca, Morelos (Mexico)

    2014-02-20

    In the core-accretion model, the nominal runaway gas-accretion phase brings most planets to multiple Jupiter masses. However, known giant planets are predominantly Jupiter mass bodies. Obtaining longer timescales for gas accretion may require using realistic equations of states, or accounting for the dynamics of the circumplanetary disk (CPD) in the low-viscosity regime, or both. Here we explore the second way by using global, three-dimensional isothermal hydrodynamical simulations with eight levels of nested grids around the planet. In our simulations, the vertical inflow from the circumstellar disk (CSD) to the CPD determines the shape of the CPD and its accretion rate. Even without a prescribed viscosity, Jupiter's mass-doubling time is ∼10{sup 4} yr, assuming the planet at 5.2 AU and a Minimum Mass Solar Nebula. However, we show that this high accretion rate is due to resolution-dependent numerical viscosity. Furthermore, we consider the scenario of a layered CSD, viscous only in its surface layer, and an inviscid CPD. We identify two planet-accretion mechanisms that are independent of the viscosity in the CPD: (1) the polar inflow—defined as a part of the vertical inflow with a centrifugal radius smaller than two Jupiter radii and (2) the torque exerted by the star on the CPD. In the limit of zero effective viscosity, these two mechanisms would produce an accretion rate 40 times smaller than in the simulation.

  7. On the Dependence of the X-Ray Burst Rate on Accretion and Spin Rate

    Science.gov (United States)

    Cavecchi, Yuri; Watts, Anna L.; Galloway, Duncan K.

    2017-12-01

    Nuclear burning and its dependence on the mass accretion rate are fundamental ingredients for describing the complicated observational phenomenology of neutron stars (NSs) in binary systems. Motivated by high-quality burst rate data emerging from large statistical studies, we report general calculations relating the bursting rate to the mass accretion rate and NS rotation frequency. In this first work, we ignore general relativistic effects and accretion topology, although we discuss where their inclusion should play a role. The relations we derive are suitable for different burning regimes and provide a direct link between parameters predicted by theory and what is to be expected in observations. We illustrate this for analytical relations of different unstable burning regimes that operate on the surface of an accreting NS. We also use the observed behavior of the burst rate to suggest new constraints on burning parameters. We are able to provide an explanation for the long-standing problem of the observed decrease of the burst rate with increasing mass accretion that follows naturally from these calculations: when the accretion rate crosses a certain threshold, ignition moves away from its initially preferred site, and this can cause a net reduction of the burst rate due to the effects of local conditions that set local differences in both the burst rate and stabilization criteria. We show under which conditions this can happen even if locally the burst rate keeps increasing with accretion.

  8. LUMBAR DISC HERNIATION

    Science.gov (United States)

    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

  9. Association between visual degeneration of intervertebral discs and the apparent diffusion coefficient.

    Science.gov (United States)

    Niinimäki, Jaakko; Korkiakoski, Arto; Ojala, Outi; Karppinen, Jaro; Ruohonen, Jyrki; Haapea, Marianne; Korpelainen, Raija; Natri, Antero; Tervonen, Osmo

    2009-06-01

    The value of apparent diffusion coefficient (ADC) measurements in intervertebral disc has been studied because ADC provides an estimate of free diffusion of unbound water and could be used as a quantitative tool to estimate degenerative changes. However, the challenging nature of diffusion imaging of spine and limited numbers of subjects in earlier studies has produced contradictory findings. We aimed to determine the relation between ADC and visual degenerative changes in lumbar intervertebral discs in a sufficiently large homogeneous study group. Lumbar spines of 228 volunteer middle-aged men were MR imaged at 1.5 T including anatomic and diffusion-weighted imaging. ADC values, T2 signal intensity and height, and width of the three lowest lumbar intervertebral discs were measured and disc degeneration visually graded. The calculated average ADC of 530 measured discs was 2.01 x 10(-3) mm(2)/s+/-0.29 (+/-S.D.). The reduction in ADC between visually normal and moderately degenerated discs was 4%. Severely degenerated discs showed 5% larger ADC values than normal discs, presumably due to free water in cracks and fissures of those discs. T2 signal intensity of the disc was significantly correlated with the ADC values, whereas other measured parameters did not show correlation. There was no evident difference in ADC between the studied anatomic lumbar levels. Because there is considerable overlap between ADC values of normal and degenerated discs, we conclude that ADC measurements of intervertebral discs, at least with current technology, have limited clinical value.

  10. Wave disc engine apparatus

    Energy Technology Data Exchange (ETDEWEB)

    Muller, Norbert; Piechna, Janusz; Sun, Guangwei; Parraga, Pablo-Francisco

    2018-01-02

    A wave disc engine apparatus is provided. A further aspect employs a constricted nozzle in a wave rotor channel. A further aspect provides a sharp bend between an inlet and an outlet in a fluid pathway of a wave rotor, with the bend being spaced away from a peripheral edge of the wave rotor. A radial wave rotor for generating electricity in an automotive vehicle is disclosed in yet another aspect.

  11. Cervical Total Disc Arthroplasty

    OpenAIRE

    Basho, Rahul; Hood, Kenneth A.

    2012-01-01

    Symptomatic adjacent segment degeneration of the cervical spine remains problematic for patients and surgeons alike. Despite advances in surgical techniques and instrumentation, the solution remains elusive. Spurred by the success of total joint arthroplasty in hips and knees, surgeons and industry have turned to motion preservation devices in the cervical spine. By preserving motion at the diseased level, the hope is that adjacent segment degeneration can be prevented. Multiple cervical disc...

  12. Total disc replacement.

    Science.gov (United States)

    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. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

  13. Percutaneous thoracic intervertebral disc nucleoplasty: technical notes from 3 patients with painful thoracic disc herniations

    NARCIS (Netherlands)

    Chua Hai Liang, N.; Gultuna, I.; Riezebos, P.; Beems, T.; Vissers, K.C.P.

    2011-01-01

    Symptomatic thoracic disc herniation is an uncommon condition and early surgical approaches were associated with significant morbidity and even mortality. We are the first to describe the technique of percutaneous thoracic nucleoplasty in three patients with severe radicular pain due to thoracic

  14. The fate of matter on accreting neutron stars

    International Nuclear Information System (INIS)

    Beard, M.; Wiescher, M.

    2003-01-01

    X-ray bursts have been identified as thermonuclear explosions on the surface of accreting neutron stars. During the thermonuclear runaway the initially hydrogen and helium rich accreted material will be rapidly converted by the rp-process towards heavy elements in the mass A=100 range. The evolution and time-scale as well as the final abundance distribution in the ashes of the thermonuclear runaway depends critically on the nuclear decay and reaction rates along the rp-process path. The paper discusses the subsequent fate of the matter due to electron capture and pycno nuclear reaction processes in the deeper layers of the neutron star crust. The necessary conditions for the ignition of pycno nuclear reactions will be presented and nuclear physics input information for a reliable determination of pycno nuclear reaction rates will be identified. (Author)

  15. Upper stellar mass limit by radiative feedback at low-metallicities: metallicity and accretion rate dependence

    Science.gov (United States)

    Fukushima, Hajime; Omukai, Kazuyuki; Hosokawa, Takashi

    2018-02-01

    We investigate the upper stellar mass limit set by radiative feedback for a forming star with various accretion rates and metallicities. Thus, we numerically solve the structures of both a protostar and its surrounding accretion envelope assuming a spherical symmetric and steady flow. The optical depth of the dust cocoon, a dusty part of the accretion envelope, differs for direct light from the stellar photosphere and diffuse light re-emitted as dust thermal emission. As a result, varying the metallicity qualitatively changes the way that the radiative feedback suppresses the accretion flow. With a fixed accretion rate of 10-3 M⊙ yr-1, both direct and diffuse light jointly operate to prevent mass accretion at Z ≳ 10-1 Z⊙. At Z ≲ 10-1 Z⊙, the diffuse light is no longer effective and the direct light solely limits the mass accretion. At Z ≲ 10-3 Z⊙, formation of the H II region plays an important role in terminating the accretion. The resultant upper mass limit increases with decreasing metallicity, from a few × 10 M⊙ to ∼103 M⊙ over Z = 1 Z⊙-10-4 Z⊙. We also illustrate how the radiation spectrum of massive star-forming cores changes with decreasing metallicity. First, the peak wavelength of the spectrum, which is located around 30 μm at 1 Z⊙, shifts to < 3 μm at Z ≲ 0.1 Z⊙. Secondly, a characteristic feature at 10 μm due to the amorphous silicate band appears as a dip at 1 Z⊙, but changes to a bump at Z ≲ 0.1 Z⊙. Using these spectral signatures, we can search massive accreting protostars in nearby low-metallicity environments with upcoming observations.

  16. Suspected herniated lumbar disc - computed tomography in differential diagnosis of non-disc-related sciatica

    Energy Technology Data Exchange (ETDEWEB)

    Weiss, T.; Koehler, D.; Treisch, J.; Claussen, C.; Felix, R.

    1984-07-01

    The most common reason a patient is referred for spinal CT examination is to exclude a ruptured intervertebral disc. Besides nerve root entrapment due to herniated disc, a number of unusual or unexpected conditions have been encountered in the course of CT lumbar spine studies. These include spondylolisthesis, spinal dysraphism, Paget's disease, and inflammatory, neoplastic, or metastatic lesions. The application of spinal (small-circle) target imaging includes the risk of overlooking soft tissue lesions that extend beyond the reconstruction circle. Therefore, complete (large-circle) circumferential abdominal scanning is recommended in case of a suspected extraspinal cause of sciatica.

  17. Total disc replacement for chronic back pain in the presence of disc degeneration.

    Science.gov (United States)

    Jacobs, Wilco; Van der Gaag, Niels A; Tuschel, Alexander; de Kleuver, Marinus; Peul, Wilco; Verbout, A J; Oner, F Cumhur

    2012-09-12

    In the search for better surgical treatment of chronic low-back pain (LBP) in the presence of disc degeneration, total disc replacement has received increasing attention in recent years. A possible advantage of total disc replacement compared with fusion is maintained mobility at the operated level, which has been suggested to reduce the chance of adjacent segment degeneration. The aim of this systematic review was to assess the effect of total disc replacement for chronic low-back pain in the presence of lumbar disc degeneration compared with other treatment options in terms of patient-centred improvement, motion preservation and adjacent segment degeneration. A comprehensive search in Cochrane Back Review Group (CBRG) trials register, CENTRAL, MEDLINE, EMBASE, BIOSIS, ISI, and the FDA register was conducted. We also checked the reference lists and performed citation tracking of included studies. We included randomised controlled trials (RCTs) comparing total disc replacement with any other intervention for degenerative disc disease. We assessed risk of bias per study using the criteria of the CBRG. Quality of evidence was graded according to the GRADE approach. Two review authors independently selected studies and assessed risk of bias of the studies. Results and upper bounds of confidence intervals were compared against predefined clinically relevant differences. We included 40 publications, describing seven unique RCT's. The follow-up of the studies was 24 months, with only one extended to five years. Five studies had a low risk of bias, although there is a risk of bias in the included studies due to sponsoring and absence of any kind of blinding. One study compared disc replacement against rehabilitation and found a statistically significant advantage in favour of surgery, which, however, did not reach the predefined threshold for clinical relevance. Six studies compared disc replacement against fusion and found that the mean improvement in VAS back pain was

  18. First results from the use of the relativistic and slim disc model SLIMULX in XSPEC

    Czech Academy of Sciences Publication Activity Database

    Caballero-García, María Dolores; Bursa, Michal; Dovčiak, Michal; Fabrika, S.; Castro-Tirado, A.J.; Karas, Vladimír

    2017-01-01

    Roč. 47, č. 2 (2017), s. 84-93 ISSN 1335-1842 R&D Projects: GA MŠk(CZ) 7E13012 EU Projects: European Commission(XE) 312789 - STRONGGRAVITY Institutional support: RVO:67985815 Keywords : accretion-discs * black hole physics * relativistic processes Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 0.336, year: 2016

  19. The Smith Cloud: surviving a high-speed transit of the Galactic disc

    Science.gov (United States)

    Tepper-García, Thor; Bland-Hawthorn, Joss

    2018-02-01

    The origin and survival of the Smith high-velocity H I cloud has so far defied explanation. This object has several remarkable properties: (i) its prograde orbit is ≈100 km s-1 faster than the underlying Galactic rotation; (ii) its total gas mass (≳ 4 × 106 M⊙) exceeds the mass of all other high-velocity clouds (HVCs) outside of the Magellanic Stream; (iii) its head-tail morphology extends to the Galactic H I disc, indicating some sort of interaction. The Smith Cloud's kinetic energy rules out models based on ejection from the disc. We construct a dynamically self-consistent, multi-phase model of the Galaxy with a view to exploring whether the Smith Cloud can be understood in terms of an infalling, compact HVC that has transited the Galactic disc. We show that while a dark-matter (DM) free HVC of sufficient mass and density can reach the disc, it does not survive the transit. The most important ingredient to survival during a transit is a confining DM subhalo around the cloud; radiative gas cooling and high spatial resolution (≲ 10pc) are also essential. In our model, the cloud develops a head-tail morphology within ∼10 Myr before and after its first disc crossing; after the event, the tail is left behind and accretes on to the disc within ∼400 Myr. In our interpretation, the Smith Cloud corresponds to a gas 'streamer' that detaches, falls back and fades after the DM subhalo, distorted by the disc passage, has moved on. We conclude that subhaloes with MDM ≲ 109 M⊙ have accreted ∼109 M⊙ of gas into the Galaxy over cosmic time - a small fraction of the total baryon budget.

  20. A pebbles accretion model with chemistry and implications for the Solar system

    Science.gov (United States)

    Ali-Dib, Mohamad

    2017-02-01

    We investigate the chemical composition of the Solar system's giant planets atmospheres using a physical formation model with chemistry. The model incorporate disc evolution, pebbles and gas accretion, type I and II migration, simplified disc photoevaporation and Solar system chemical measurements. We track the chemical compositions of the formed giant planets and compare them to the observed values. Two categories of models are studied: with and without disc chemical enrichment via photoevaporation (PE). Predictions for the oxygen and nitrogen abundances, core masses and total amount of heavy elements for the planets are made for each case. We find that in the case without disc PE, both Jupiter and Saturn will have a small residual core and comparable total amounts of heavy elements in the envelopes. We predict oxygen abundances enrichments in the same order as carbon, phosphorus and sulfur for both planets. Cometary nitrogen abundances does not allow us to easily reproduce Jupiter's nitrogen observations. In the case with disc PE, less core erosion is needed to reproduce the chemical composition of the atmospheres, so both planets will end up with possibly more massive residual cores and higher total mass of heavy elements. It is also significantly easier to reproduce Jupiter's nitrogen abundance. No single disc was found to form both Jupiter and Saturn with all their constraints in the case without photoevaporation. No model was able to fit the constraints on Uranus and Neptune, hinting towards a more complicated formation mechanism for these planets. The predictions of these models should be compared to the upcoming Juno measurements to better understand the origins of the Solar system giant planets.

  1. Mismatch and misalignment: dark haloes and satellites of disc galaxies

    Science.gov (United States)

    Deason, A. J.; McCarthy, I. G.; Font, A. S.; Evans, N. W.; Frenk, C. S.; Belokurov, V.; Libeskind, N. I.; Crain, R. A.; Theuns, T.

    2011-08-01

    We study the phase-space distribution of satellite galaxies associated with late-type galaxies in the GIMIC suite of simulations. GIMIC consists of resimulations of five cosmologically representative regions from the Millennium Simulation, which have higher resolution and incorporate baryonic physics. Whilst the disc of the galaxy is well aligned with the inner regions (r˜ 0.1r200) of the dark matter halo, both in shape and angular momentum, there can be substantial misalignments at larger radii (r˜r200). Misalignments of >45° are seen in ˜30 per cent of our sample. We find that the satellite population aligns with the shape (and angular momentum) of the outer dark matter halo. However, the alignment with the galaxy is weak owing to the mismatch between the disc and dark matter halo. Roughly 20 per cent of the satellite systems with 10 bright galaxies within r200 exhibit a polar spatial alignment with respect to the galaxy - an orientation reminiscent of the classical satellites of the Milky Way. We find that a small fraction (˜10 per cent) of satellite systems show evidence for rotational support which we attribute to group infall. There is a bias towards satellites on prograde orbits relative to the spin of the dark matter halo (and to a lesser extent with the angular momentum of the disc). This preference towards co-rotation is stronger in the inner regions of the halo where the most massive satellites accreted at relatively early times are located. We attribute the anisotropic spatial distribution and angular momentum bias of the satellites at z= 0 to their directional accretion along the major axes of the dark matter halo. The satellite galaxies have been accreted relatively recently compared to the dark matter mass and have experienced less phase-mixing and relaxation - the memory of their accretion history can remain intact to z= 0. Understanding the phase-space distribution of the z= 0 satellite population is key for studies that estimate the host halo

  2. Quiescent Light Curve of Accreting Neutron Star MAXI J0556-332

    Science.gov (United States)

    Liu, Helei; Matsuo, Yasuhide; Hashimoto, Masa-aki; Noda, Tsuneo; Fujimoto, Masayuki Y.

    2017-12-01

    MAXI J0556-332 is the hottest transient accreting neutron star at the beginning of its quiescence. A theoretical model with crustal heating indicates that an additional shallow heat source of Qshallow > 6 MeV per accreted nucleon is required in the shallow outer crust with respect to the deeper star crust by considering the observed decline in accretion rate at the end of outburst. However, the physical source of this shallow heating is still unclear. In the present investigation, we performed stellar evolutionary calculations, adopting the effects of outburst behavior of the accretion rate. As a consequence, we find that the quiescent light curve of MAXI J0556-332 can be well explained by the nuclear energy generation due to the hot CNO cycle.

  3. Late veneer and late accretion to the terrestrial planets

    Science.gov (United States)

    Brasser, R.; Mojzsis, S. J.; Werner, S. C.; Matsumura, S.; Ida, S.

    2016-12-01

    It is generally accepted that silicate-metal ('rocky') planet formation relies on coagulation from a mixture of sub-Mars sized planetary embryos and (smaller) planetesimals that dynamically emerge from the evolving circum-solar disc in the first few million years of our Solar System. Once the planets have, for the most part, assembled after a giant impact phase, they continue to be bombarded by a multitude of planetesimals left over from accretion. Here we place limits on the mass and evolution of these planetesimals based on constraints from the highly siderophile element (HSE) budget of the Moon. Outcomes from a combination of N-body and Monte Carlo simulations of planet formation lead us to four key conclusions about the nature of this early epoch. First, matching the terrestrial to lunar HSE ratio requires either that the late veneer on Earth consisted of a single lunar-size impactor striking the Earth before 4.45 Ga, or that it originated from the impact that created the Moon. An added complication is that analysis of lunar samples indicates the Moon does not preserve convincing evidence for a late veneer like Earth. Second, the expected chondritic veneer component on Mars is 0.06 weight percent. Third, the flux of terrestrial impactors must have been low (≲10-6 M⊕ Myr-1) to avoid wholesale melting of Earth's crust after 4.4 Ga, and to simultaneously match the number of observed lunar basins. This conclusion leads to an Hadean eon which is more clement than assumed previously. Last, after the terrestrial planets had fully formed, the mass in remnant planetesimals was ∼10-3 M⊕, lower by at least an order of magnitude than most previous models suggest. Our dynamically and geochemically self-consistent scenario requires that future N-body simulations of rocky planet formation either directly incorporate collisional grinding or rely on pebble accretion.

  4. Steepest descent approximations for accretive operator equations

    International Nuclear Information System (INIS)

    Chidume, C.E.

    1993-03-01

    A necessary and sufficient condition is established for the strong convergence of the steepest descent approximation to a solution of equations involving quasi-accretive operators defined on a uniformly smooth Banach space. (author). 49 refs

  5. The physics of accretion onto black holes

    CERN Document Server

    Belloni, Tomaso; Casella, Piergiorgio; Gilfanov, Marat; Jonker, Peter; King, Andrew

    2015-01-01

    This title reviews in-depth research on accretion on all scales, from galactic binaries to intermediate mass and supermassive black holes. Possible future directions of accretion are also discussed. The following main themes are covered: a historical perspective; physical models of accretion onto black holes of all masses; black hole fundamental parameters; and accretion, jets and outflows. An overview and outlook on the topic is also presented.  This volume summarizes the status of the study of astrophysical black hole research and is aimed at astrophysicists and graduate students working in this field.  Originally published in Space Science Reviews, Vol 183/1-4, 2014.

  6. Accretion of Ghost Condensate by Black Holes

    Energy Technology Data Exchange (ETDEWEB)

    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.

  7. Time-Dependent Variations of Accretion Disk

    Directory of Open Access Journals (Sweden)

    Hye-Weon Na

    1987-06-01

    Full Text Available In dward nova we assume the primary star as a white dwarf and the secondary as the late type star which filled Roche lobe. Mass flow from the secondary star leads to the formation of thin accretion disk around the white dwarf. We use the α parameter as viscosity to maintain the disk form and propose that the outburst in dwarf nova cause the steep increase of source term. With these assumptions we solve the basic equations of stellar structure using Newton-Raphson method. We show the physical parameters like temperature, density, pressure, opacity, surface density, height and flux to the radius of disk. Changing the value of α, we compare several parameters when mass flow rate is constant with those of when luminosity of disk is brightest. At the same time, we obtain time-dependent variations of luminosity and mass of disk. We propose the suitable range of α is 0.15-0.18 to the difference of luminosity. We compare several parameters of disk with those of the normal late type stars which have the same molecular weight of disk is lower. Maybe the outburst in dwarf nova is due to the variation of the α value instead of increment of mass flow from the secondary star.

  8. First results from the use of the relativistic and slim disc model SLIMULX in XSPEC

    Science.gov (United States)

    Caballero-Garcia, M. D.; Bursa, M.; Dovčiak, M.; Fabrika, S.; Castro-Tirado, A. J.; Karas, V.

    2017-07-01

    Ultra-Luminous X-ray sources (ULXs) are accreting black holes for which their X-ray properties have been seen to be different to the case of stellar-mass black hole binaries. For most of the cases their intrinsic energy spectra are well described by a cold accretion disc (thermal) plus a curved high-energy emission components. The mass of the black hole (BH) derived from the thermal disc component is usually in the range of 100-1000 solar masses, which have led to the idea that this might represent strong evidence of the Intermediate Mass Black Holes (IMBH), proposed to exist by theoretical studies but with no firm detection (as a class) so far. Recent theoretical and observational developments are leading towards the idea that these sources are instead stellar-mass BHs accreting at an unusual super-Eddington regime. In this paper we briefly describe the model SLIMULX that can be used in XSPEC for the fit of thermal spectra of slim discs around stellar mass BHs in the super-Eddington regime. This model consistently takes all relativistic effects into account. We present the obtained results from the fit of the X-ray spectra from NGC 5408 X—1.

  9. Baseline Assessment of Net Calcium Carbonate Accretion Rates on U.S. Pacific Reefs.

    Directory of Open Access Journals (Sweden)

    Bernardo Vargas-Ángel

    Full Text Available This paper presents a comprehensive quantitative baseline assessment of in situ net calcium carbonate accretion rates (g CaCO3 cm(-2 yr(-1 of early successional recruitment communities on Calcification Accretion Unit (CAU plates deployed on coral reefs at 78 discrete sites, across 11 islands in the central and south Pacific Oceans. Accretion rates varied substantially within and between islands, reef zones, levels of wave exposure, and island geomorphology. For forereef sites, mean accretion rates were the highest at Rose Atoll, Jarvis, and Swains Islands, and the lowest at Johnston Atoll and Tutuila. A comparison between reef zones showed higher accretion rates on forereefs compared to lagoon sites; mean accretion rates were also higher on windward than leeward sites but only for a subset of islands. High levels of spatial variability in net carbonate accretion rates reported herein draw attention to the heterogeneity of the community assemblages. Percent cover of key early successional taxa on CAU plates did not reflect that of the mature communities present on surrounding benthos, possibly due to the short deployment period (2 years of the experimental units. Yet, net CaCO3 accretion rates were positively correlated with crustose coralline algae (CCA percent cover on the surrounding benthos and on the CAU plates, which on average represented >70% of the accreted material. For foreeefs and lagoon sites combined CaCO3 accretion rates were statistically correlated with total alkalinity and Chlorophyll-a; a GAM analysis indicated that SiOH and Halimeda were the best predictor variables of accretion rates on lagoon sites, and total alkalinity and Chlorophyll-a for forereef sites, demonstrating the utility of CAUs as a tool to monitor changes in reef accretion rates as they relate to ocean acidification. This study underscores the pivotal role CCA play as a key benthic component and supporting actively calcifying reefs; high Mg-calcite exoskeletons

  10. Baseline Assessment of Net Calcium Carbonate Accretion Rates on U.S. Pacific Reefs.

    Science.gov (United States)

    Vargas-Ángel, Bernardo; Richards, Cristi L; Vroom, Peter S; Price, Nichole N; Schils, Tom; Young, Charles W; Smith, Jennifer; Johnson, Maggie D; Brainard, Russell E

    2015-01-01

    This paper presents a comprehensive quantitative baseline assessment of in situ net calcium carbonate accretion rates (g CaCO3 cm(-2) yr(-1)) of early successional recruitment communities on Calcification Accretion Unit (CAU) plates deployed on coral reefs at 78 discrete sites, across 11 islands in the central and south Pacific Oceans. Accretion rates varied substantially within and between islands, reef zones, levels of wave exposure, and island geomorphology. For forereef sites, mean accretion rates were the highest at Rose Atoll, Jarvis, and Swains Islands, and the lowest at Johnston Atoll and Tutuila. A comparison between reef zones showed higher accretion rates on forereefs compared to lagoon sites; mean accretion rates were also higher on windward than leeward sites but only for a subset of islands. High levels of spatial variability in net carbonate accretion rates reported herein draw attention to the heterogeneity of the community assemblages. Percent cover of key early successional taxa on CAU plates did not reflect that of the mature communities present on surrounding benthos, possibly due to the short deployment period (2 years) of the experimental units. Yet, net CaCO3 accretion rates were positively correlated with crustose coralline algae (CCA) percent cover on the surrounding benthos and on the CAU plates, which on average represented >70% of the accreted material. For foreeefs and lagoon sites combined CaCO3 accretion rates were statistically correlated with total alkalinity and Chlorophyll-a; a GAM analysis indicated that SiOH and Halimeda were the best predictor variables of accretion rates on lagoon sites, and total alkalinity and Chlorophyll-a for forereef sites, demonstrating the utility of CAUs as a tool to monitor changes in reef accretion rates as they relate to ocean acidification. This study underscores the pivotal role CCA play as a key benthic component and supporting actively calcifying reefs; high Mg-calcite exoskeletons makes CCA

  11. Lumbar disc degeneration is an equally important risk factor as lumbar fusion for causing adjacent segment disc disease.

    Science.gov (United States)

    Natarajan, Raghu N; Andersson, Gunnar B J

    2017-01-01

    Treatment of degenerative spinal disorders by fusion produces abnormal mechanical conditions at mobile segments above or below the site of spinal disorders and is clinically referred to as adjacent segments disc disease (ASDD) or transition syndrome in the case of a previous surgical treatment. The aim of the current study is to understand with the help of poro-elastic finite element models how single or two level degeneration of lower lumbar levels influences motions at adjacent levels and compare the findings to motions produced by single or two level fusions when the adjacent disk has varying degree of degeneration. Validated grade-specific finite element models including varying grades of disc degeneration at lower lumbar levels with and without fusion were developed and used to determine motions at all levels of the lumbar spine due to applied moment loads. Results showed that adjacent disc motions do depend on severity of disc degeneration, number of disc degenerated or fused, and level at which degeneration or fusion occurred. Furthermore, single level degeneration and single level fusion produced similar amount of adjacent disc motions. The pattern of increase in adjacent segment motions due to disc degeneration and increase in motions at segment adjacent to fusion was similar. Based on the current study, it can be concluded that disc degeneration should also be considered as a risk factor in addition to fusion for generating adjacent disc degeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:123-130, 2017. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

  12. Aerodynamics and thermal physics of helicopter ice accretion

    Science.gov (United States)

    Han, Yiqiang

    Ice accretion on aircraft introduces significant loss in airfoil performance. Reduced lift-to- drag ratio reduces the vehicle capability to maintain altitude and also limits its maneuverability. Current ice accretion performance degradation modeling approaches are calibrated only to a limited envelope of liquid water content, impact velocity, temperature, and water droplet size; consequently inaccurate aerodynamic performance degradations are estimated. The reduced ice accretion prediction capabilities in the glaze ice regime are primarily due to a lack of knowledge of surface roughness induced by ice accretion. A comprehensive understanding of the ice roughness effects on airfoil heat transfer, ice accretion shapes, and ultimately aerodynamics performance is critical for the design of ice protection systems. Surface roughness effects on both heat transfer and aerodynamic performance degradation on airfoils have been experimentally evaluated. Novel techniques, such as ice molding and casting methods and transient heat transfer measurement using non-intrusive thermal imaging methods, were developed at the Adverse Environment Rotor Test Stand (AERTS) facility at Penn State. A novel heat transfer scaling method specifically for turbulent flow regime was also conceived. A heat transfer scaling parameter, labeled as Coefficient of Stanton and Reynolds Number (CSR = Stx/Rex --0.2), has been validated against reference data found in the literature for rough flat plates with Reynolds number (Re) up to 1x107, for rough cylinders with Re ranging from 3x104 to 4x106, and for turbine blades with Re from 7.5x105 to 7x106. This is the first time that the effect of Reynolds number is shown to be successfully eliminated on heat transfer magnitudes measured on rough surfaces. Analytical models for ice roughness distribution, heat transfer prediction, and aerodynamics performance degradation due to ice accretion have also been developed. The ice roughness prediction model was

  13. [Temporomandibular joint disc surgery].

    Science.gov (United States)

    Potier, J; Maes, J-M; Nicot, R; Dumousseau, T; Cotelle, M; Ferri, J

    2016-09-01

    Temporomandibular joint (TMJ) disorders are a common disease and may be responsible for major functional and painful repercussions. Treatment is not consensual. The literature highlights the role of conservative treatments (physiotherapy, analgesics, splints) in a first attempt. Minimally invasive surgical techniques (arthroscopy, arthrocentesis) have developed rapidly in recent decades. They have proven effective and reliable, especially in patients suffering from irreducible or reducible anterior disc dislocation or presenting with arthopathies. The goal of our work was to make an update about disk surgery. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

  14. Linking channel hydrology with riparian wetland accretion in tidal rivers

    Science.gov (United States)

    Ensign, Scott H.; Noe, Gregory B.; Hupp, Cliff R.

    2014-01-01

    The hydrologic processes by which tide affects river channel and riparian morphology within the tidal freshwater zone are poorly understood, yet are fundamental to predicting the fate of coastal rivers and wetlands as sea level rises. We investigated patterns of sediment accretion in riparian wetlands along the non-tidal through oligohaline portion of two coastal plain rivers in Maryland, U.S.A., and how flow velocity, water level, and suspended sediment concentration (SSC) in the channel may have contributed to those patterns. Sediment accretion was measured over a one year period using artificial marker horizons, channel hydrology was measured over a one month period using acoustic Doppler current profilers, and SSC was predicted from acoustic backscatter. Riparian sediment accretion was lowest at the non-tidal sites (mean and standard deviation = 8 ± 8 mm yr-1), highest at the upstream tidal freshwater forested wetlands (TFFW) (33 ± 28 mm yr-1), low at the midstream TFFW (12 ± 9 mm yr-1), and high at the oligohaline (fresh-to-brackish) marshes (19 ± 8 mm yr-1). Channel maximum flood and ebb velocity was 2-fold faster at the oligohaline than tidal freshwater zone on both tidal rivers, corresponding with the differences in in-channel SSC: the oligohaline zone's SSC was more than double the tidal freshwater zone's, and was greater than historical SSC at the non-tidal gages. The tidal wave characteristics differed between rivers, leading to significantly greater in-channel SSC during floodplain inundation in the weakly convergent than the strongly convergent tidal river. Overall sediment accretion was higher in the embayed river likely due to a single storm discharge and associated sedimentation.

  15. Herniated lumbar disc: injection interventions for sciatica

    OpenAIRE

    Jordan, Joanne L; Konstantinou, Kika; O'Dowd, John

    2016-01-01

    Herniated lumbar disc is a displacement of disc material (nucleus pulposus or annulus fibrosus) beyond the intervertebral disc space. The highest prevalence is among people aged 30 to 50 years, with a male to female ratio of 2:1.

  16. Structures formation through self-organized accretion on cosmic strings

    International Nuclear Information System (INIS)

    Murdzek, R.

    2009-01-01

    In this paper, we shall show that the formation of structures through accretion by a cosmic string is driven by a natural feed-back mechanism: a part of the energy radiated by accretions creates a pressure on the accretion disk itself. This phenomenon leads to a nonlinear evolution of the accretion process. Thus, the formation of structures results as a consequence of a self-organized growth of the accreting central object.

  17. Swift observations of V404 Cyg during the 2015 outburst: X-ray outflows from super-Eddington accretion

    Science.gov (United States)

    Motta, S. E.; Kajava, J. J. E.; Sánchez-Fernández, C.; Beardmore, A. P.; Sanna, A.; Page, K. L.; Fender, R.; Altamirano, D.; Charles, P.; Giustini, M.; Knigge, C.; Kuulkers, E.; Oates, S.; Osborne, J. P.

    2017-10-01

    The black hole (BH) binary V404 Cyg entered the outburst phase in 2015 June after 26 yr of X-ray quiescence, and with its behaviour broke the outburst evolution pattern typical of most BH binaries. We observed the entire outburst with the Swift satellite and performed time-resolved spectroscopy of its most active phase, obtaining over a thousand spectra with exposures from tens to hundreds of seconds. All the spectra can be fitted with an absorbed power-law model, which most of the time required the presence of a partial covering. A blueshifted iron-Kα line appears in 10 per cent of the spectra together with the signature of high column densities, and about 20 per cent of the spectra seem to show signatures of reflection. None of the spectra showed the unambiguous presence of soft disc-blackbody emission, while the observed bolometric flux exceeded the Eddington value in 3 per cent of the spectra. Our results can be explained assuming that the inner part of the accretion flow is inflated into a slim disc that both hides the innermost (and brightest) regions of the flow, and produces a cold, clumpy, high-density outflow that introduces the high absorption and fast spectral variability observed. We argue that the BH in V404 Cyg might have been accreting erratically or even continuously at Eddington/super-Eddington rates - thus sustaining a surrounding slim disc - while being partly or completely obscured by the inflated disc and its outflow. Hence, the largest flares produced by the source might not be accretion-driven events, but instead the effects of the unveiling of the extremely bright source hidden within the system.

  18. The late inspiral of supermassive black hole binaries with circumbinary gas discs in the LISA band

    Science.gov (United States)

    Tang, Yike; Haiman, Zoltán; MacFadyen, Andrew

    2018-02-01

    We present the results of 2D, moving-mesh, viscous hydrodynamical simulations of an accretion disc around a merging supermassive black hole binary (SMBHB). The simulation is pseudo-Newtonian, with the BHs modeled as point masses with a Paczynski-Wiita potential, and includes viscous heating, shock heating, and radiative cooling. We follow the gravitational inspiral of an equal-mass binary with a component mass Mbh = 106M⊙ from an initial separation of 60rg (where rg ≡ GMbh/c2 is the gravitational radius) to the merger. We find that a central, low-density cavity forms around the binary, as in previous work, but that the BHs capture gas from the circumbinary disc and accrete efficiently via their own minidiscs, well after their inspiral outpaces the viscous evolution of the disc. The system remains luminous, displaying strong periodicity at twice the binary orbital frequency throughout the entire inspiral process, all the way to the merger. In the soft X-ray band, the thermal emission is dominated by the inner edge of the circumbinary disc with especially clear periodicity in the early inspiral. By comparison, harder X-ray emission is dominated by the minidiscs, and the light curve is initially more noisy but develops a clear periodicity in the late inspiral stage. This variability pattern should help identify the EM counterparts of SMBHBs detected by the space-based gravitational-wave detector LISA.

  19. Measuring the spins of accreting black holes

    International Nuclear Information System (INIS)

    McClintock, Jeffrey E; Narayan, Ramesh; Gou, Lijun; Kulkarni, Akshay; Penna, Robert F; Steiner, James F; Davis, Shane W; Orosz, Jerome A; Remillard, Ronald A

    2011-01-01

    A typical galaxy is thought to contain tens of millions of stellar-mass black holes, the collapsed remnants of once massive stars, and a single nuclear supermassive black hole. Both classes of black holes accrete gas from their environments. The accreting gas forms a flattened orbiting structure known as an accretion disk. During the past several years, it has become possible to obtain measurements of the spins of the two classes of black holes by modeling the x-ray emission from their accretion disks. Two methods are employed, both of which depend upon identifying the inner radius of the accretion disk with the innermost stable circular orbit, whose radius depends only on the mass and spin of the black hole. In the Fe Kα method, which applies to both classes of black holes, one models the profile of the relativistically broadened iron line with a special focus on the gravitationally redshifted red wing of the line. In the continuum-fitting (CF) method, which has so far only been applied to stellar-mass black holes, one models the thermal x-ray continuum spectrum of the accretion disk. We discuss both methods, with a strong emphasis on the CF method and its application to stellar-mass black holes. Spin results for eight stellar-mass black holes are summarized. These data are used to argue that the high spins of at least some of these black holes are natal, and that the presence or absence of relativistic jets in accreting black holes is not entirely determined by the spin of the black hole.

  20. Radicular interdural lumbar disc herniation

    Science.gov (United States)

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

    2009-01-01

    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. PMID:19888608

  1. Accreting neutron stars by QFT

    Science.gov (United States)

    Chen, Shao-Guang

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

  2. Extremes of the jet-accretion power relation of blazars, as explored by NuSTAR

    DEFF Research Database (Denmark)

    Sbarrato, T.; Ghisellini, G.; Tagliaferri, G.

    2016-01-01

    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...

  3. Relativistic Disc Line: A Tool to Constrain Neutron Star Equation of State Models

    Science.gov (United States)

    Bhattacharyya, Sudip

    2017-09-01

    Relativistic iron Kα spectral emission line from the inner disc of a neutron star Low-Mass X-ray Binary (LMXB) was first detected in 2007. This discovery opened up new ways to probe strong gravity and dense matter. The past decade has seen detections of such a line from many neutron star LMXBs, and confirmation of this line from the same source with several X-ray satellites. These have firmly established the new field of relativistic disc line from neutron star systems in only a decade or so. Fitting the shape of such a line with an appropriate general relativistic model provides the accretion disc inner edge radius to the stellar mass ratio. In this review, we briefly discuss how an accurate measurement of this ratio with a future larger area X-ray instrument can be used to constrain neutron star equation of state models.

  4. Accretion signatures in the X-shooter spectrum of the substellar companion to SR12

    Science.gov (United States)

    Santamaría-Miranda, Alejandro; Cáceres, Claudio; Schreiber, Matthias R.; Hardy, Adam; Bayo, Amelia; Parsons, Steven G.; Gromadzki, Mariusz; Aguayo Villegas, Aurora Belén

    2018-04-01

    About a dozen substellar companions orbiting young stellar objects or pre-main sequence stars at several hundred au have been identified in the last decade. These objects are interesting both due to the uncertainties surrounding their formation, and because their large separation from the host star offers the potential to study the atmospheres of young giant planets and brown dwarfs. Here, we present X-shooter spectroscopy of SR 12 C, a ˜2 Myr young brown dwarf orbiting SR 12 at an orbital separation of 1083 au. We determine the spectral type, gravity, and effective temperature via comparison with models and observational templates of young brown dwarfs. In addition, we detect and characterize accretion using several accretion tracers. We find SR 12 C to be a brown dwarf of spectral type L0 ± 1, log g = 4 ± 0.5, an effective temperature of 2600 ± 100 K. Our spectra provide clear evidence for accretion at a rate of ˜10-10 M⊙ yr-1. This makes SR 12 one of the few sub-stellar companions with a reliable estimate for its accretion rate. A comparison of the ages and accretion rates of sub-stellar companions with young isolated brown dwarfs does not reveal any significant differences. If further accretion rate measurements of a large number of substellar companions can confirm this trend, this would hint towards a similar formation mechanism for substellar companions at large separations and isolated brown dwarfs.

  5. [Endovascular repair of iliocaval arteriovenous fistula complicating lumbar disc surgery].

    Science.gov (United States)

    Ben Jemaa, H; Maalej, A; Lazzez, K; Jemal, H; Karray, S; Ben Mahfoudh, K

    2016-05-01

    Vascular complications of lumbar disc surgery are rare. Few cases have been reported. Arteriovenous fistulas are the most common. They are due to anatomical relationships between the last lumbar vertebrae, the corresponding discs, and the iliac vessels; degenerative lesions of the intervertebral discs facilitate instrumental vessel perforation, and operative difficulty. Computed tomography is particularly accurate for making the diagnosis. Treatment strategies consist in surgery or endovascular management. Percutaneous endovascular treatment using a stent-graft is a reasonable option for treating arteriovenous fistula. We describe the case of a 50-year-old patient who developed an iliocaval arteriovenous fistula following lumbar disc hernia surgery. The lesion was excluded by a stent-graft. The postoperative period was uneventful. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

  6. Wetland Accretion Rates Along Coastal Louisiana: Spatial and Temporal Variability in Light of Hurricane Isaac’s Impacts

    Directory of Open Access Journals (Sweden)

    Thomas A. Bianchette

    2015-12-01

    Full Text Available The wetlands of the southern Louisiana coast are disappearing due to a host of environmental stressors. Thus, it is imperative to analyze the spatial and temporal variability of wetland vertical accretion rates. A key question in accretion concerns the role of landfalling hurricanes as a land-building agent, due to their propensity to deposit significant volumes of inorganic sediments. Since 1996, thousands of accretion measurements have been made at 390 sites across coastal Louisiana as a result of a regional monitoring network, called the Coastal Reference Monitoring System (CRMS. We utilized this dataset to analyze the spatial and temporal patterns of accretion by mapping rates during time periods before, around, and after the landfall of Hurricane Isaac (2012. This analysis is vital for quantifying the role of hurricanes as a land-building agent and for understanding the main mechanism causing heightened wetland accretion. The results show that accretion rates averaged about 2.89 cm/year from stations sampled before Isaac, 4.04 cm/year during the period encompassing Isaac, and 2.38 cm/year from sites established and sampled after Isaac. Accretion rates attributable to Isaac’s effects were therefore 40% and 70% greater than before and after the event, respectively, indicating the event’s importance toward coastal land-building. Accretion associated with Isaac was highest at sites located 70 kilometers from the storm track, particularly those near the Mississippi River and its adjacent distributaries and lakes. This spatial pattern of elevated accretion rates indicates that freshwater flooding from fluvial channels, rather than storm surge from the sea per se, is the main mechanism responsible for increased wetland accretion. This significance of riverine flooding has implications toward future coastal restoration policies and practices.

  7. Validation of 3-D Ice Accretion Measurement Methodology for Experimental Aerodynamic Simulation

    Science.gov (United States)

    Broeren, Andy P.; Addy, Harold E., Jr.; Lee, Sam; Monastero, Marianne C.

    2015-01-01

    Determining the adverse aerodynamic effects due to ice accretion often relies on dry-air wind-tunnel testing of artificial, or simulated, ice shapes. Recent developments in ice-accretion documentation methods have yielded a laser-scanning capability that can measure highly three-dimensional (3-D) features of ice accreted in icing wind tunnels. The objective of this paper was to evaluate the aerodynamic accuracy of ice-accretion simulations generated from laser-scan data. Ice-accretion tests were conducted in the NASA Icing Research Tunnel using an 18-in. chord, two-dimensional (2-D) straight wing with NACA 23012 airfoil section. For six ice-accretion cases, a 3-D laser scan was performed to document the ice geometry prior to the molding process. Aerodynamic performance testing was conducted at the University of Illinois low-speed wind tunnel at a Reynolds number of 1.8 × 10(exp 6) and a Mach number of 0.18 with an 18-in. chord NACA 23012 airfoil model that was designed to accommodate the artificial ice shapes. The ice-accretion molds were used to fabricate one set of artificial ice shapes from polyurethane castings. The laser-scan data were used to fabricate another set of artificial ice shapes using rapid prototype manufacturing such as stereolithography. The iced-airfoil results with both sets of artificial ice shapes were compared to evaluate the aerodynamic simulation accuracy of the laser-scan data. For five of the six ice-accretion cases, there was excellent agreement in the iced-airfoil aerodynamic performance between the casting and laser-scan based simulations. For example, typical differences in iced-airfoil maximum lift coefficient were less than 3 percent with corresponding differences in stall angle of approximately 1 deg or less. The aerodynamic simulation accuracy reported in this paper has demonstrated the combined accuracy of the laser-scan and rapid-prototype manufacturing approach to simulating ice accretion for a NACA 23012 airfoil. For several

  8. Magnetically gated accretion in an accreting ‘non-magnetic’ white dwarf

    Science.gov (United States)

    Scaringi, S.; Maccarone, T. J.; D’Angelo, C.; Knigge, C.; Groot, P. J.

    2017-12-01

    White dwarfs are often found in binary systems with orbital periods ranging from tens of minutes to hours in which they can accrete gas from their companion stars. In about 15 per cent of these binaries, the magnetic field of the white dwarf is strong enough (at 106 gauss or more) to channel the accreted matter along field lines onto the magnetic poles. The remaining systems are referred to as ‘non-magnetic’, because until now there has been no evidence that they have a magnetic field that is strong enough to affect the accretion dynamics. Here we report an analysis of archival optical observations of the ‘non-magnetic’ accreting white dwarf in the binary system MV Lyrae, whose light curve displays quasi-periodic bursts of about 30 minutes duration roughly every 2 hours. The timescale and amplitude of these bursts indicate the presence of an unstable, magnetically regulated accretion mode, which in turn implies the existence of magnetically gated accretion, in which disk material builds up around the magnetospheric boundary (at the co-rotation radius) and then accretes onto the white dwarf, producing bursts powered by the release of gravitational potential energy. We infer a surface magnetic field strength for the white dwarf in MV Lyrae of between 2 × 104 gauss and 1 × 105 gauss, too low to be detectable by other current methods. Our discovery provides a new way of studying the strength and evolution of magnetic fields in accreting white dwarfs and extends the connections between accretion onto white dwarfs, young stellar objects and neutron stars, for which similar magnetically gated accretion cycles have been identified.

  9. Bondi-Hoyle-Lyttleton Accretion onto Binaries

    Science.gov (United States)

    Antoni, Andrea; MacLeod, Morgan; Ramírez-Ruiz, Enrico

    2018-01-01

    Binary stars are not rare. While only close binary stars will eventually interact with one another, even the widest binary systems interact with their gaseous surroundings. The rates of accretion and the gaseous drag forces arising in these interactions are the key to understanding how these systems evolve. This poster examines accretion flows around a binary system moving supersonically through a background gas. We perform three-dimensional hydrodynamic simulations of Bondi-Hoyle-Lyttleton accretion using the adaptive mesh refinement code FLASH. We simulate a range of values of semi-major axis of the orbit relative to the gravitational focusing impact parameter of the pair. On large scales, gas is gravitationally focused by the center-of-mass of the binary, leading to dynamical friction drag and to the accretion of mass and momentum. On smaller scales, the orbital motion imprints itself on the gas. Notably, the magnitude and direction of the forces acting on the binary inherit this orbital dependence. The long-term evolution of the binary is determined by the timescales for accretion, slow down of the center-of-mass, and decay of the orbit. We use our simulations to measure these timescales and to establish a hierarchy between them. In general, our simulations indicate that binaries moving through gaseous media will slow down before the orbit decays.

  10. Thermal structure of the accreting earth

    Science.gov (United States)

    Turcotte, D. L.; Pflugrath, J. C.

    1985-01-01

    The energy associated with the accretion of the earth and the segregation of the core is more than sufficient to melt the entire earth. In order to understand the thermal evolution of the early earth it is necessary to study the relevant heat transfer mechanisms. In this paper the existence of a global magma ocean is postulated and calculations are carried out of the heat flux through it in order to determine its depth. In the solid mantle heat is transferred by the upward migration of magma. This magma supplies the magma ocean. The increase in the mantle liquidus with depth (pressure) is the dominant effect influencing heat transfer through the magma ocean. It is found that a magma ocean with a depth of the order of 20 km would have existed as the earth accreted. It is concluded that the core segregated and an atmosphere was formed during accretion.

  11. Continuum Reverberation Mapping of AGN Accretion Disks

    Energy Technology Data Exchange (ETDEWEB)

    Fausnaugh, Michael M. [Department of Astronomy, Ohio State University, Columbus, OH (United States); MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA (United States); Peterson, Bradley M. [Department of Astronomy, Ohio State University, Columbus, OH (United States); Center for Cosmology and AstroParticle Physics, Ohio State University, Columbus, OH (United States); Space Telescope Science Institute, Baltimore, MD (United States); Starkey, David A. [SUPA Physics and Astronomy, University of St. Andrews, Scotland (United Kingdom); Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL (United States); Horne, Keith, E-mail: faus@mit.edu [SUPA Physics and Astronomy, University of St. Andrews, Scotland (United Kingdom); Collaboration: the AGN STORM Collaboration

    2017-12-05

    We show recent detections of inter-band continuum lags in three AGN (NGC 5548, NGC 2617, and MCG+08-11-011), which provide new constraints on the temperature profiles and absolute sizes of the accretion disks. We find lags larger than would be predicted for standard geometrically thin, optically thick accretion disks by factors of 2.3–3.3. For NGC 5548, the data span UV through optical/near-IR wavelengths, and we are able to discern a steeper temperature profile than the T ~ R{sup −3/4} expected for a standard thin disk. Using a physical model, we are also able to estimate the inclinations of the disks for two objects. These results are similar to those found from gravitational microlensing of strongly lensed quasars, and provide a complementary approach for investigating the accretion disk structure in local, low luminosity AGN.

  12. Cosmological Accretion Disks via External Radiation Drag

    OpenAIRE

    FUKUE, Jun; UMEMURA, Masayuki

    1994-01-01

    Accretion disks as well as disk accretion driven by external radiation drag are presented under a steady approximation in the cases of the point-mass potential and of the dark-matter potential. We assume that the external drag force can be expressed as -beta_v, where (beta) is a constant coefficient and v the velocity vector. When the gravitational potential is given by a central point-mass M, we find, in a cold regime where the pressure force is neglected, steady solutions such that the infa...

  13. Self-Consistent Models of Accretion Disks

    Science.gov (United States)

    Narayan, Ramesh

    2000-01-01

    Research was carried out on several topics in the theory of astrophysical accretion flows around black holes, neutron stars and white dwarfs. The focus of our effort was the advection-dominated accretion flow (ADAF) model which the PI and his collaborators proposed and developed over the last several years. Our group completed a total of 46 papers, of which 36 are in refereed journals and 12 are in conference proceedings. All the papers have either already appeared in print or are in press.

  14. Are galaxy discs optically thick?

    International Nuclear Information System (INIS)

    Disney, Michael; Davies, Jonathan; Phillipps, Steven

    1989-01-01

    We re-examine the classical optical evidence for the low optical depths traditionally assigned to spiral discs and argue that it is highly model-dependent and unconvincing. In particular, layered models with a physically thin but optically thick dust layer behave like optically thin discs. The opposite hypotheses, that such discs are optically thick is then examined in the light of modern evidence. We find it to be consistent with the near-infrared and IRAS observations, with the surface brightnesses, with the HI and CO column densities and with the Hα measurements. (author)

  15. Can accretion disk properties distinguish gravastars from black holes?

    International Nuclear Information System (INIS)

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

    2009-01-01

    Gravastars, hypothetic astrophysical objects, consisting of a dark energy condensate surrounded by a strongly correlated thin shell of anisotropic matter, have been proposed as an alternative to the standard black hole picture of general relativity. Observationally distinguishing between astrophysical black holes and gravastars is a major challenge for this latter theoretical model. This is due to the fact that in static gravastars large stability regions (of the transition layer of these configurations) exist that are sufficiently close to the expected position of the event horizon, so that it would be difficult to distinguish the exterior geometry of gravastars from an astrophysical black hole. However, in the context of stationary and axially symmetrical geometries, a possibility of distinguishing gravastars from black holes is through the comparative study of thin accretion disks around rotating gravastars and Kerr-type black holes, respectively. In the present paper, we consider accretion disks around slowly rotating gravastars, with all the metric tensor components estimated up to the second order in the angular velocity. Due to the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution and equilibrium radiation spectrum) are different for these two classes of compact objects, consequently giving clear observational signatures. In addition to this, it is also shown that the conversion efficiency of the accreting mass into radiation is always smaller than the conversion efficiency for black holes, i.e. gravastars provide a less efficient mechanism for converting mass to radiation than black holes. Thus, these observational signatures provide the possibility of clearly distinguishing rotating gravastars from Kerr-type black holes.

  16. Degenerated human intervertebral discs contain autoantibodies against extracellular matrix proteins

    Directory of Open Access Journals (Sweden)

    S Capossela

    2014-04-01

    Full Text Available Degeneration of intervertebral discs (IVDs is associated with back pain and elevated levels of inflammatory cells. It has been hypothesised that discogenic pain is a direct result of vascular and neural ingrowth along annulus fissures, which may expose the avascular nucleus pulposus (NP to the systemic circulation and induce an autoimmune reaction. In this study, we confirmed our previous observation of antibodies in human degenerated and post-traumatic IVDs cultured in vitro. We hypothesised that the presence of antibodies was due to an autoimmune reaction against specific proteins of the disc. Furthermore we identified antigens which possibly trigger an autoimmune response in degenerative disc diseases. We demonstrated that degenerated and post-traumatic IVDs contain IgG antibodies against typical extracellular proteins of the disc, particularly proteins of the NP. We identified IgGs against collagen type II and aggrecan, confirming an autoimmune reaction against the normally immune privileged NP. We also found specific IgGs against collagens types I and V, but not against collagen type III. In conclusion, this study confirmed the association between disc degeneration and autoimmunity, and may open the avenue for future studies on developing prognostic, diagnostic and therapy-monitoring markers for degenerative disc diseases.

  17. Laser Disc Decompression In Emam Khomeini Hospital 1996-1999

    Directory of Open Access Journals (Sweden)

    Ghaffar Poor. M

    2002-07-01

    Full Text Available Low back pain is among the most frequent medical complaints and a major public health problem. 1.7 percent of cases are caused by herniated disc, 20 percent of which require interventional treatment. Percutaneous laser disc decompression (P.L.DD can be considered as an effective therapeutic alternative in certain cases."nMaterials and Methods: To determine the efficacy of this method in Iran in patient's with low back pain due to disc herniation, 40 patients according to medical history, physical examination and MRI findings were selected for this study. Patients who had canal stenosis, marginal, osteophyte, advanced disc dehydration, ruptured posterior ligament and other contraindication were excluded. CT scan was used only for needle navigation. After proper positioning of needle, nucleous pulposus was evapourated with Nd-YAG laser. Total energy was 1200-1600j. The procedure was done out patient and follow up has been done at 1 day, 1 week, 1,3, 6 and 12 months."nResults: There was no serious complication. 80 percent of patients in one-year follow up showed significant clinical improvement."nConclusion: Our findings suggests that percutaneous laser disc decompression can be considered as an effective alternative method of treatment for disc herniation and patient selection is the critical factor which determines success rate.

  18. Supermassive black hole feeding and star formation in massive accretion discs

    Czech Academy of Sciences Publication Activity Database

    Šubr, Ladislav

    2008-01-01

    Roč. 79, č. 4 (2008), s. 1071-1074 ISSN 0037-8720. [Central Kiloparsec - Active Galactic Nuclei and Their Hosts. Ierapetra, Crete, 04.06.2008-06.06.2008] R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : black holes Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  19. Warm absorber and truncated accretion disc in IRAS 05078+1626

    Czech Academy of Sciences Publication Activity Database

    Svoboda, Jiří; Guainazzi, M.; Karas, Vladimír

    2010-01-01

    Roč. 512, Mar-Apr (2010), A62/1-A62/8 ISSN 0004-6361 R&D Projects: GA ČR GD205/09/H033; GA ČR GA205/07/0052 Grant - others:ESA(XE) ESA-PECS project No. 98040; Univerzita Karlova(CZ) GAUK 33308 Institutional research plan: CEZ:AV0Z10030501 Keywords : galaxies: active * galaxies: Seyfert * galaxies: individual: IRAS 05078+1626 Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.410, year: 2010

  20. Polarization signatures of strong gravity in active galactic nuclei accretion discs

    Czech Academy of Sciences Publication Activity Database

    Dovčiak, Michal; Karas, Vladimír; Matt, G.

    2004-01-01

    Roč. 355, č. 3 (2004), s. 1005-1009 ISSN 0035-8711 R&D Projects: GA ČR GA202/02/0735; GA ČR GA205/03/0902 Institutional research plan: CEZ:AV0Z1003909 Keywords : relativity * polarization * galaxies Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.238, year: 2004

  1. [Treatment of thoracic disc herniation. Case report].

    Science.gov (United States)

    Picado-Baca, Mauricio Leonardo; Mireles-Cano, José Nicolás; León-Meza, Víctor Manuel; García-González, Oscar Guillermo; Ramos-Trujillo, Alejandro

    2016-01-01

    Herniated thoracic intervertebral disc is a rare cause of spinal cord compression. Its frequency varies from 0.15% to 1.7% of all disc herniations, and produces symptoms in 0.5% to 0.8%. Case 1. A 50-year-old woman, with pain and burning sensation in left hemithorax of four months of onset. It was treated as a herpetic syndrome, with no improvement. She was seen after thirteen days of exacerbation of clinical symptoms. The physical examination showed asymmetric paraparesis, lower left pelvic limb 1/5, and right pelvic limb 3/5¸ sensory level T8, with left Babinski positive. A thoracic disc herniation in space T8-T9 was diagnosed. A 55-year-old patient with a history of presenting pain in lumbar area of 5 years onset. She also had radicular pain that radiated to the right pelvic limb, with intensity 10/10 on a Visual Analogue Scale. Her physical examination showed muscle strength 5/5, with normal sensitivity in all dermatomes and tendon reflexes, and a positive right Babinski. Thoracic disc herniation T7-T8 level was diagnosed. Due to anatomical conditions that define this type of hernia, the extracavitary posterolateral approach should be the recommended surgical procedure when the simultaneously performed anterior decompression and fixation with posterior instrumentation are the treatments proposed. Despite the different anatomical structures of this special area, it was possible to obtain satisfactory results for both clinical cases. Copyright © 2015 Academia Mexicana de Cirugía A.C. Publicado por Masson Doyma México S.A. All rights reserved.

  2. Transient events in bright debris discs: Collisional avalanches revisited

    Science.gov (United States)

    Thebault, P.; Kral, Q.

    2018-01-01

    Context. A collisional avalanche is set off by the breakup of a large planetesimal, releasing vast amounts of small unbound grains that enter a debris disc located further away from the star, triggering there a collisional chain reaction that could potentially create detectable transient structures. Aims: We investigate this mechanism, using for the first time a fully self-consistent code coupling dynamical and collisional evolutions. We also quantify for the first time the photometric evolution of the system and investigate whether or not avalanches could explain the short-term luminosity variations recently observed in some extremely bright debris discs. Methods: We use the state-of-the-art LIDT-DD code. We consider an avalanche-favoring A6V star, and two set-ups: a "cold disc" case, with a dust release at 10 au and an outer disc extending from 50 to 120 au, and a "warm disc" case with the release at 1 au and a 5-12 au outer disc. We explore, in addition, two key parameters: the density (parameterized by its optical depth τ) of the main outer disc and the amount of dust released by the initial breakup. Results: We find that avalanches could leave detectable structures on resolved images, for both "cold" and "warm" disc cases, in discs with τ of a few 10-3, provided that large dust masses (≳1020-5 × 1022 g) are initially released. The integrated photometric excess due to an avalanche is relatively limited, less than 10% for these released dust masses, peaking in the λ 10-20 μm domain and becoming insignificant beyond 40-50 μm. Contrary to earlier studies, we do not obtain stronger avalanches when increasing τ to higher values. Likewise, we do not observe a significant luminosity deficit, as compared to the pre-avalanche level, after the passage of the avalanche. These two results concur to make avalanches an unlikely explanation for the sharp luminosity drops observed in some extremely bright debris discs. The ideal configuration for observing an

  3. The life cycles of Be viscous decretion discs: time-dependent modelling of infrared continuum observations

    Science.gov (United States)

    Vieira, R. G.; Carciofi, A. C.; Bjorkman, J. E.; Rivinius, Th.; Baade, D.; Rímulo, L. R.

    2017-01-01

    We apply the viscous decretion disc (VDD) model to interpret the infrared disc continuum emission of 80 Be stars observed in different epochs. In this way, we determined 169 specific disc structures, namely their density scale, ρ0, and exponent, n. We found that the n values range mainly between 1.5 and 3.5, and ρ0 varies between 10-12 and 10-10 g cm-3, with a peak close to the lower value. Our large sample also allowed us to firmly establish that the discs around early-type stars are denser than in late-type stars. Additionally, we estimated the disc mass decretion rates and found that they range between 10-12 and 10-9 M⊙ yr-1. These values are compatible with recent stellar evolution models of fast-rotating stars. One of the main findings of this work is a correlation between the ρ0 and n values. In order to find out whether these relations can be traced back to the evolution of discs or have some other origin, we used the VDD model to calculate temporal sequences under different assumptions for the time profile of the disc mass injection. The results support the hypothesis that the observed distribution of disc properties is due to a common evolutionary path. In particular, our results suggest that the time-scale for disc growth, during which the disc is being actively fed by mass injection episodes, is shorter than the time-scale for disc dissipation, when the disc is no longer fed by the star and dissipates as a result of the viscous diffusion of the disc material.

  4. Cooling of Accretion-Heated Neutron Stars

    Science.gov (United States)

    Wijnands, Rudy; Degenaar, Nathalie; Page, Dany

    2017-09-01

    We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.

  5. Ice Accretion on Wind Turbine Blades

    DEFF Research Database (Denmark)

    Hudecz, Adriána; Koss, Holger; Hansen, Martin Otto Laver

    2013-01-01

    forces were monitored as ice was building up on the airfoil for glaze, rime and mixed ice. In the first part of the numerical analysis, the resulted ice profiles of the wind tunnel tests were compared to profiles estimated by using the 2D ice accretion code TURBICE. In the second part, Ansys Fluent...

  6. Probing thermonuclear burning on accreting neutron stars

    NARCIS (Netherlands)

    Keek, L.

    2008-01-01

    Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes

  7. QPOs and Resonance in Accretion Disks

    Czech Academy of Sciences Publication Activity Database

    Kluzniak, W.; Abramowicz, M. A.; Bursa, Michal; Török, G.

    2007-01-01

    Roč. 27, Marzo 2007 (2007), s. 18-25 ISSN 1405-2059 R&D Projects: GA AV ČR IAA300030510 Institutional research plan: CEZ:AV0Z10030501 Keywords : quasi-periodic oscillations * accretion disks * general relativity Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  8. On the resonant behavior of longitudinally vibrating accreting rods

    CSIR Research Space (South Africa)

    Shatalov, M

    2012-09-01

    Full Text Available The theory of accreting structures is a new and fast developing branch of analytical mechanics basing on the theory of partial differential and integral equations. In the present paper the authors analyze qualitative properties of accreting rods...

  9. EARTH, MOON, SUN, AND CV ACCRETION DISKS

    International Nuclear Information System (INIS)

    Montgomery, M. M.

    2009-01-01

    Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar, and black hole systems. We find that spinning, tilted CV DN systems cannot be described by a precessing ring or by a precessing rigid disk. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our analysis indicates that the best description of a retrogradely precessing spinning, tilted, CV DN accretion disk is a differentially rotating, tilted disk with an attached rotating, tilted ring located near the innermost disk annuli. In agreement with the observations and numerical simulations by others, we find that our numerically simulated CV DN accretion disks retrogradely precess as a unit. Our final, reduced expression for retrograde precession agrees well with our numerical simulation results and with selective observational systems that seem to have main-sequence secondaries. Our results suggest that a major source to retrograde precession is tidal torques like that by the Moon and the Sun on the Earth. In addition, these tidal torques should be common to a variety of systems where one member is spinning and tilted, regardless if

  10. Comparison of Animal Discs Used in Disc Research to Human Lumbar Disc: Torsion Mechanics and Collagen Content

    Science.gov (United States)

    Showalter, Brent L.; Beckstein, Jesse C.; Martin, John T.; Beattie, Elizabeth E.; Orías, Alejandro A. Espinoza; Schaer, Thomas P.; Vresilovic, Edward J.; Elliott, Dawn M.

    2012-01-01

    Study Design Experimental measurement and normalization of in vitro disc torsion mechanics and collagen content for several animal species used in intervertebral disc research and comparing these to the human disc. Objective To aid in the selection of appropriate animal models for disc research by measuring torsional mechanical properties and collagen content. Summary of Background Data There is lack of data and variability in testing protocols for comparing animal and human disc torsion mechanics and collagen content. Methods Intervertebral disc torsion mechanics were measured and normalized by disc height and polar moment of inertia for 11 disc types in 8 mammalian species: the calf, pig, baboon, goat, sheep, rabbit, rat, and mouse lumbar, and cow, rat, and mouse caudal. Collagen content was measured and normalized by dry weight for the same discs except the rat and mouse. Collagen fiber stretch in torsion was calculated using an analytical model. Results Measured torsion parameters varied by several orders of magnitude across the different species. After geometric normalization, only the sheep and pig discs were statistically different from human. Fiber stretch was found to be highly dependent on the assumed initial fiber angle. The collagen content of the discs was similar, especially in the outer annulus where only the calf and goat discs were statistically different from human. Disc collagen content did not correlate with torsion mechanics. Conclusion Disc torsion mechanics are comparable to human lumbar discs in 9 of 11 disc types after normalization by geometry. The normalized torsion mechanics and collagen content of the multiple animal discs presented is useful for selecting and interpreting results for animal models of the disc. Structural composition of the disc, such as initial fiber angle, may explain the differences that were noted between species after geometric normalization. PMID:22333953

  11. Pathogenesis of optic disc edema in raised intracranial pressure.

    Science.gov (United States)

    Hayreh, Sohan Singh

    2016-01-01

    raised CSFP in patients, by evaluating optic disc and fundus changes by stereoscopic fundus photography and fluorescein fundus angiography. Based on the combined information from all the studies discussed above, it is clear that the pathogenesis of optic disc edema in raised intracranial pressure is a mechanical phenomenon. It is primarily due to a rise of CSFP in the optic nerve sheath, which produces axoplasmic flow stasis in the optic nerve fibers in the surface nerve fiber layer and prelaminar region of the optic nerve head. Axoplasmic flow stasis then results in swelling of the nerve fibers, and consequently of the optic disc. Swelling of the nerve fibers and of the optic disc secondarily compresses the fine, low-pressure venules in that region, resulting in venous stasis and fluid leakage; that leads to the accumulation of extracellular fluid. Contrary to the previous theories, the various vascular changes seen in optic disc edema are secondary and not primary. Thus, optic disc edema in raised CSFP is due to a combination of swollen nerve fibers and the accumulation of extracellular fluid. My studies also provided information about the pathogeneses of visual disturbances in raised intracranial pressure. Copyright © 2015 Elsevier Ltd. All rights reserved.

  12. Lumbar disc excision through fenestration

    Directory of Open Access Journals (Sweden)

    Sangwan S

    2006-01-01

    Full Text Available Background : Lumbar disc herniation often causes sciatica. Many different techniques have been advocated with the aim of least possible damage to other structures while dealing with prolapsed disc surgically in the properly selected and indicated cases. Methods : Twenty six patients with clinical symptoms and signs of prolapsed lumbar intervertebral disc having radiological correlation by MRI study were subjected to disc excision by interlaminar fenestration method. Results : The assessment at follow-up showed excellent results in 17 patients, good in 6 patients, fair in 2 patients and poor in 1 patient. The mean preoperative and postoperative Visual Analogue Scores were 9.34 ±0.84 and 2.19 ±0.84 on scale of 0-10 respectively. These were statistically significant (p value< 0.001, paired t test. No significant complications were recorded. Conclusion : Procedures of interlaminar fenestration and open disc excision under direct vision offers sufficient adequate exposure for lumbar disc excision with a smaller incision, lesser morbidity, shorter convalescence, early return to work and comparable overall results in the centers where recent laser and endoscopy facilities are not available.

  13. Disc piezoelectric ceramic transformers.

    Science.gov (United States)

    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.

  14. Probing neutron star physics using accreting neutron stars

    NARCIS (Netherlands)

    Patruno, A.

    2010-01-01

    We give an obervational overview of the accreting neutron stars systems as probes of neutron star physics. In particular we focus on the results obtained from the periodic timing of accreting millisecond X-ray pulsars in outburst and from the measurement of X-ray spectra of accreting neutron stars

  15. Spherical Accretion in a Uniformly Expanding Universe

    Science.gov (United States)

    Colpi, Monica; Shapiro, Stuart L.; Wasserman, Ira

    1996-10-01

    We consider spherically symmetric accretion of material from an initially homogeneous, uniformly expanding medium onto a Newtonian point mass M. The gas is assumed to evolve adiabatically with a constant adiabatic index F, which we vary over the range Γ ɛ [1, 5/3]. We use a one-dimensional Lagrangian code to follow the spherical infall of material as a function of time. Outflowing shells gravitationally bound to the point mass fall back, giving rise to a inflow rate that, after a rapid rise, declines as a power law in time. If there were no outflow initially, Bondi accretion would result, with a characteristic accretion time-scale ta,0. For gas initially expanding at a uniform rate, with a radial velocity U = R/t0 at radius R, the behavior of the flow at all subsequent times is determined by ta,0/t0. If ta,0/t0 ≫ 1, the gas has no time to respond to pressure forces, so the fluid motion is nearly collisionless. In this case, only loosely bound shells are influenced by pressure gradients and are pushed outward. The late-time evolution of the mass accretion rate Mdot is close to the result for pure dust, and we develop a semianalytic model that accurately accounts for the small effect of pressure gradients in this limit. In the opposite regime, ta,0/t0 ≪ 1, pressure forces significantly affect the motion of the gas. At sufficiently early times, t ≤ ttr, the flow evolved along a sequence of quasi-stationary, Bondi-like states, with a time-dependent Mdot determined by the slowly varying gas density at large distances. However, at later times, t ≥ ttr, the fluid flow enters a dustllke regime; ttr is the time when the instantaneous Bondi accretion radius reaches the marginally bound radius. The transition time ttr depends sensitively on ta,0/t0 for a given Γ and can greatly exceed t0. We show that there exists a critical value Γ = 11/9, below which the transition from fluid to ballistic motion disappears. As one application of our calculations, we consider the

  16. Role of local absorption on the X-ray emission from MHD accretion shocks in classical T Tauri stars

    Directory of Open Access Journals (Sweden)

    Bonito

    2014-01-01

    Full Text Available Accretion processes onto classical T Tauri stars (CTTSs are believed to generate shocks at the stellar surface due to the impact of supersonic downflowing plasma. Although current models of accretion streams provide a plausible global picture of this process, several aspects are still unclear. For example, the observed X-ray luminosity in accretion shocks is, in general, well below the predicted value. A possible explanation discussed in the literature is in terms of significant absorption of the emission due to the thick surrounding medium. Here we consider a 2D MHD model describing an accretion stream propagating through the atmosphere of a CTTS and impacting onto its chromosphere. The model includes all the relevant physics, namely the gravity, the thermal conduction, and the radiative cooling, and a realistic description of the unperturbed stellar atmosphere (from the chromosphere to the corona. From the model results, we synthesize the X-ray emission emerging from the hot slab produced by the accretion shock, exploring different configurations and strengths of the stellar magnetic field. The synthesis includes the local absorption by the thick surrounding medium and the Doppler shift of lines due to the component of plasma velocity along the line-of-sight. We explore the effects of absorption on the emerging X-ray spectrum, considering different inclinations of the accretion stream with respect to the observer. Finally we compare our results with the observations.

  17. Imbalanced Protein Expression Patterns of Anabolic, Catabolic, Anti-Catabolic and Inflammatory Cytokines in Degenerative Cervical Disc Cells: New Indications for Gene Therapeutic Treatments of Cervical Disc Diseases

    Science.gov (United States)

    Mern, Demissew S.; Beierfuß, Anja; Fontana, Johann; Thomé, Claudius; Hegewald, Aldemar A.

    2014-01-01

    Degenerative disc disease (DDD) of the cervical spine is common after middle age and can cause loss of disc height with painful nerve impingement, bone and joint inflammation. Despite the clinical importance of these problems, in current publications the pathology of cervical disc degeneration has been studied merely from a morphologic view point using magnetic resonance imaging (MRI), without addressing the issue of biological treatment approaches. So far a wide range of endogenously expressed bioactive factors in degenerative cervical disc cells has not yet been investigated, despite its importance for gene therapeutic approaches. Although degenerative lumbar disc cells have been targeted by different biological treatment approaches, the quantities of disc cells and the concentrations of gene therapeutic factors used in animal models differ extremely. These indicate lack of experimentally acquired data regarding disc cell proliferation and levels of target proteins. Therefore, we analysed proliferation and endogenous expression levels of anabolic, catabolic, ant-catabolic, inflammatory cytokines and matrix proteins of degenerative cervical disc cells in three-dimensional cultures. Preoperative MRI grading of cervical discs was used, then grade III and IV nucleus pulposus (NP) tissues were isolated from 15 patients, operated due to cervical disc herniation. NP cells were cultured for four weeks with low-glucose in collagen I scaffold. Their proliferation rates were analysed using 3-(4, 5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide. Their protein expression levels of 28 therapeutic targets were analysed using enzyme-linked immunosorbent assay. During progressive grades of degeneration NP cell proliferation rates were similar. Significantly decreased aggrecan and collagen II expressions (P<0.0001) were accompanied by accumulations of selective catabolic and inflammatory cytokines (disintegrin and metalloproteinase with thrombospondin motifs 4 and 5, matrix

  18. The effect of catastrophic collisional fragmentation and diffuse medium accretion on a computational interstellar dust system

    International Nuclear Information System (INIS)

    Liffman, K.

    1990-01-01

    The effects of catastrophic collisional fragmentation and diffuse medium accretion on a the interstellar dust system are computed using a Monte Carlo computer model. The Monte Carlo code has as its basis an analytic solution of the bulk chemical evolution of a two-phase interstellar medium, described by Liffman and Clayton (1989). The model is subjected to numerous different interstellar processes as it transfers from one interstellar phase to another. Collisional fragmentation was found to be the dominant physical process that shapes the size spectrum of interstellar dust. It was found that, in the diffuse cloud phase, 90 percent of the refractory material is locked up in the dust grains, primarily due to accretion in the molecular medium. This result is consistent with the observed depletions of silicon. Depletions were found to be affected only slightly by diffuse cloud accretion. 42 refs

  19. The ALMA early science view of FUor/EXor objects - V. Continuum disc masses and sizes

    Science.gov (United States)

    Cieza, Lucas A.; Ruíz-Rodríguez, Dary; Perez, Sebastian; Casassus, Simon; Williams, Jonathan P.; Zurlo, Alice; Principe, David A.; Hales, Antonio; Prieto, Jose L.; Tobin, John J.; Zhu, Zhaohuan; Marino, Sebastian

    2018-03-01

    Low-mass stars build a significant fraction of their total mass during short outbursts of enhanced accretion known as FUor and EXor outbursts. FUor objects are characterized by a sudden brightening of ˜5 mag at visible wavelengths within 1 yr and remain bright for decades. EXor objects have lower amplitude outbursts on shorter time-scales. Here we discuss a 1.3 mm Atacama Large Millimeter/submillimeter Array (ALMA) mini-survey of eight outbursting sources (three FUors, four EXors, and the borderline object V1647 Ori) in the Orion Molecular Cloud. While previous papers in this series discuss the remarkable molecular outflows observed in the three FUor objects and V1647 Ori, here we focus on the continuum data and the differences and similarities between the FUor and EXor populations. We find that FUor discs are significantly more massive (˜80-600 MJup) than the EXor objects (˜0.5-40 MJup). We also report that the EXor sources lack the prominent outflows seen in the FUor population. Even though our sample is small, the large differences in disc masses and outflow activity suggest that the two types of objects represent different evolutionary stages. The FUor sources seem to be rather compact (Rc < 20-40 au) and to have a smaller characteristic radius for a given disc mass when compared to T Tauri stars. V1118 Ori, the only known close binary system in our sample, is shown to host a disc around each one of the stellar components. The disc around HBC 494 is asymmetric, hinting at a structure in the outer disc or the presence of a second disc.

  20. Early Results from NICER Observations of Accreting Neutron Stars

    Science.gov (United States)

    Chakrabarty, Deepto; Ozel, Feryal; Arzoumanian, Zaven; Gendreau, Keith C.; Bult, Peter; Cackett, Ed; Chenevez, Jerome; Fabian, Andy; Guillot, Sebastien; Guver, Tolga; Homan, Jeroen; Keek, Laurens; Lamb, Frederick; Ludlam, Renee; Mahmoodifar, Simin; Markwardt, Craig B.; Miller, Jon M.; Psaltis, Dimitrios; Strohmayer, Tod E.; Wilson-Hodge, Colleen A.; Wolff, Michael T.

    2018-01-01

    The Neutron Star Interior Composition Explorer (NICER) offers significant new capabilities for the study of accreting neuton stars relative to previous X-ray missions including large effective area, low background, and greatly improved low-energy response. The NICER Burst and Accretion Working Group has designed a 2 Ms observation program to study a number of phenomena in accreting neutron stars including type-I X-ray bursts, superbursts, accretion-powered pulsations, quasi-periodic oscillations, and accretion disk reflection spectra. We present some early results from the first six months of the NICER mission.

  1. The vertical structure of gaseous galaxy discs in cold dark matter haloes

    Science.gov (United States)

    Benítez-Llambay, Alejandro; Navarro, Julio F.; Frenk, Carlos S.; Ludlow, Aaron D.

    2018-01-01

    We study the vertical structure of polytropic centrifugally supported gaseous discs embedded in cold dark matter (CDM) haloes. At fixed radius, R, the shape of the vertical density profile depends weakly on whether the disc is self-gravitating (SG) or non-self-gravitating (NSG). The disc 'characteristic' thickness, zH, set by the midplane sound speed and circular velocity, zNSG = (cs/Vc)R, in the NSG case, and by the sound speed and surface density, z_SG = c_s^2/GΣ, in SG discs, is smaller than zSG and zNSG. SG discs are typically Toomre unstable, NSG discs are stable. Exponential discs in CDM haloes with roughly flat circular velocity curves 'flare' outwards. Flares in mono abundance or coeval populations in galaxies like the Milky Way are thus not necessarily due to radial migration. For the polytropic equation of state of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations, discs that match observational constraints are NSG for Md smoothed particle hydrodynamic simulations and find excellent agreement. Our results clarify the role of the gravitational softening on the thickness of simulated discs, and on the onset of radial instabilities. EAGLE low-mass discs are NSG so the softening plays no role in their vertical structure. High-mass discs are expected to be SG and unstable, and may be artificially thickened and stabilized unless gravity is well resolved. Simulations with spatial resolution high enough to not compromise the vertical structure of a disc also resolve the onset of their instabilities, but the converse is not true.

  2. Extracellular matrix remodeling in experimental intervertebral disc degeneration.

    Science.gov (United States)

    de Oliveira, Cintia Pereira; Rodrigues, Luciano Miller Reis; Fregni, Maria Vitória Ventura Dias; Gotfryd, Alberto; Made, Ana Maria; Pinhal, Maria Aparecida da Silva

    2013-05-01

    To evaluate the remodeling of the extracellular matrix in intervertebral disc degeneration through the experimental model of intervertebral disc degeneration. The model of disc degeneration induction, using needle 20G and 360° rotation, was applied for 30 seconds between the 6(th)/7(th), and 8(th)/9(th) coccygeal vertebrae of Wistar rats. The intermediary level, between the 7(th) and 8(th) vertebrae, was taken as control, not being subjected puncture. The distribution of the extracellular matrix components involved in the remodeling and inflammation process, such as proteoglycans (aggrecan, decorin, biglycan), growth factors (TGFβ), heparanase isoforms (HPSE1, HPSE2), metaloprotesasis-9 (MMP9) and interleukins (IL-6, IL-10) was analyzed during the post-injury period (15 to 30 days) and in the control group (discs collected immediately after the puncture, day zero). On the 15(th) day, acute phase of the disease, a reduced expression of extracellular matrix components had been observed, whilst there were no differences in the interleukins expression. At 30 days, the molecules followed a very similar pattern of expression in the control group (not affected by disc degeneration). The results show that during the acute phase significant alterations in the extracellular matrix components occur and in the late phase intervertebral disc returns to a profile similar to noninvolved tissue, probably due to extensive remodeling process of the extracellular matrix that is capable of regenerating the damaged tissue. : The experimental model used demonstrated the occurrence of significant changes in the extracellular matrix during the period analyzed after induction of intervertebral disc degeneration. Laboratory investigation.

  3. Genetic association studies in lumbar disc degeneration: a systematic review.

    Directory of Open Access Journals (Sweden)

    Pasi J Eskola

    Full Text Available Low back pain is associated with lumbar disc degeneration, which is mainly due to genetic predisposition. The objective of this study was to perform a systematic review to evaluate genetic association studies in lumbar disc degeneration as defined on magnetic resonance imaging (MRI in humans.A systematic literature search was conducted in MEDLINE, MEDLINE In-Process, SCOPUS, ISI Web of Science, The Genetic Association Database and The Human Genome Epidemiology Network for information published between 1990-2011 addressing genes and lumbar disc degeneration. Two investigators independently identified studies to determine inclusion, after which they performed data extraction and analysis. The level of cumulative genetic association evidence was analyzed according to The HuGENet Working Group guidelines.Fifty-two studies were included for review. Forty-eight studies reported at least one positive association between a genetic marker and lumbar disc degeneration. The phenotype definition of lumbar disc degeneration was highly variable between the studies and replications were inconsistent. Most of the associations presented with a weak level of evidence. The level of evidence was moderate for ASPN (D-repeat, COL11A1 (rs1676486, GDF5 (rs143383, SKT (rs16924573, THBS2 (rs9406328 and MMP9 (rs17576.Based on this first extensive systematic review on the topic, the credibility of reported genetic associations is mostly weak. Clear definition of lumbar disc degeneration phenotypes and large population-based cohorts are needed. An international consortium is needed to standardize genetic association studies in relation to disc degeneration.

  4. The hard X-ray emission spectra from accretion columns in intermediate polars

    Science.gov (United States)

    Yi, Insu; Vishniac, Ethan T.

    1994-01-01

    We consider the hard (greater than 2 keV) X-ray emission from accretion columns in an intermediate polar system, GK Per, using a simple settling solution. The rate of photon emission per logarithmic energy interval can be fitted with a power law, E(exp -gamma), with gamma approximately 2.0, in agreement with observations. This index is only weakly dependent on the mass accretion rate, dot-M, for dot-M in the range of a few times 10(exp 16-18) g/s. The peak energy of the photon spectra (after photoelectric absorption) is expected to be E(sub p) approximately (5 keV) gamma(exp -1/3) (N(sub H)/10(exp 23)/sq cm)(exp 1/3) where N(sub H) is the hydrogen column density along the line of sight. The observed spectra of GK Per and possibly of V1223 Sgr suggest N(sub H) approximately 10(exp 23)/sq cm. This large N(sub H) may be due to partially ionized preshock column material. Alternatively, we also consider absorption by the cool outer parts of an accretion disk. In this case the photoelectric absorption depth in the disk is a sensitive function of inclination. For GK Per the required inclination is approximately 83 deg. For mass accretion rates larger than a critical rate of approximately 10(exp 18) g/s, X-ray emission from the column accretion is significantly affected by radiation drag. Although the mass accretion rate increases dramatically during outbursts, the observed hard (greater than 2 keV) X-ray luminosity will not rise proportionately. The slope and peak energy of the outburst spectra are only weakly affected. We conclude that the observed X-ray spectra can be explained by this simple analytic solution and that the production of hard X-rays from the accretion shock at the magnetic poles in the intermediate polars is in general agreement with the observations. However, since the X-ray emission and absorption depend on the mass accretion rate in a complicated manner, observed hard X-ray luminosities (greater than 2 keV) are not a good indicator of the mass

  5. Volatile accretion history of the Earth.

    Science.gov (United States)

    Wood, B J; Halliday, A N; Rehkämper, M

    2010-10-28

    It has long been thought that the Earth had a protracted and complex history of volatile accretion and loss. Albarède paints a different picture, proposing that the Earth first formed as a dry planet which, like the Moon, was devoid of volatile constituents. He suggests that the Earth's complement of volatile elements was only established later, by the addition of a small veneer of volatile-rich material at ∼100 Myr (here and elsewhere, ages are relative to the origin of the Solar System). Here we argue that the Earth's mass balance of moderately volatile elements is inconsistent with Albarède's hypothesis but is well explained by the standard model of accretion from partially volatile-depleted material, accompanied by core formation.

  6. Diffusion time scales and accretion in the sun

    International Nuclear Information System (INIS)

    Michaud, G.

    1977-01-01

    It is thought that surface abundances in the Sun could be due largely to accretion either of comets or grains, and it has been suggested that if surface convection zones were smaller than is usually indicated by model calculations, accretion would be especially important. Unless the zone immediately below the surface convection zone is sufficiently stable for diffusion to be important, other transport processes, such as turbulence and meridional circulation, more efficient than diffusion, will tend to homogenise the Sun. Diffusion is the slowest of the transport processes and will become important when other transport processes become inoperative. Using diffusion theory the minimum mass of the convection zone can be determined in order that transport processes at the bottom of the zone are not to influence abundances in the convection zone. If diffusion time scales are shorter than the life of the star (Sun) diffusion will modify the abundances in the convection zone. The mass in the convection zone for which diffusion time scales are equal to the life of the star on the main sequence then determines the minimum mass in the convection zone that justifies neglect of transport processes at the bottom of the convection zone. It is calculated here that, for the Sun, this mass is between 3 x 10 -3 and 10 -2 solar mass, and a general explosion is derived for the diffusion time scale as a function of the mass of the convection zone. (U.K.)

  7. ON THE LAMPPOST MODEL OF ACCRETING BLACK HOLES

    Energy Technology Data Exchange (ETDEWEB)

    Niedźwiecki, Andrzej; Szanecki, Michał [Łódź University, Department of Physics, Pomorska 149/153, 90-236 Łódź (Poland); Zdziarski, Andrzej A. [Centrum Astronomiczne im. M. Kopernika, Bartycka 18, 00-716 Warszawa (Poland)

    2016-04-10

    We study the lamppost model, in which the X-ray source in accreting black hole (BH) systems is located on the rotation axis close to the horizon. We point out a number of inconsistencies in the widely used lamppost model relxilllp, e.g., neglecting the redshift of the photons emitted by the lamppost that are directly observed. They appear to invalidate those model fitting results for which the source distances from the horizon are within several gravitational radii. Furthermore, if those results were correct, most of the photons produced in the lamppost would be trapped by the BH, and the luminosity generated in the source as measured at infinity would be much larger than that observed. This appears to be in conflict with the observed smooth state transitions between the hard and soft states of X-ray binaries. The required increase of the accretion rate and the associated efficiency reduction also present a problem for active galactic nuclei. Then, those models imply the luminosity measured in the local frame is much higher than that produced in the source and measured at infinity, due to the additional effects of time dilation and redshift, and the electron temperature is significantly higher than that observed. We show that these conditions imply that the fitted sources would be out of the e{sup ±} pair equilibrium. On the other hand, the above issues pose relatively minor problems for sources at large distances from the BH, where relxilllp can still be used.

  8. Blob accretion in AM Herculis systems

    International Nuclear Information System (INIS)

    Litchfield, S.J.; King, A.R.

    1990-01-01

    We calculate self-consistent hydrostatic temperature distributions for the atmosphere of a white dwarf in an AM Herculis system on to which a discrete blob has accreted. We show that the surface derived from this temperature structure does not produce soft X-ray light curves characteristic of the anomalous X-ray state of AM Herculis. We suggest that non-hydrostatic splashes are a more likely origin for the light curves. (author)

  9. Stress analysis in a functionally graded disc under mechanical loads ...

    Indian Academy of Sciences (India)

    Some relative results for the stress and displacement components along the radius are presented due to internal pressure, external pressure, centrifugal force and steady state temperature. From the results, it is found that the grading indexes play an important role in determining the thermomechanical responses of FG disc ...

  10. Accretion and primary differentiation of Mars

    International Nuclear Information System (INIS)

    Drake, M.J.

    1988-01-01

    In collecting samples from Mars to address questions such as whether Mars accreted homogeneously or heterogeneously, how Mars segregated into a metallic core and silicate mantle, and whether Mars outgassed catastrophically coincident with accretion or more serenely on a longer timescale, we must be guided by our experience in addressing these questions for the Earth, Moon, and igneous meteorite parent bodies. A key measurement to be made on any sample returned from Mars is its oxygen isotopic composition. A single measurement will suffice to bind the SNC meteorites to Mars or demonstrate that they cannot be samples of that planet. A positive identification of Mars as the SNC parent planet will permit all that has been learned from the SNC meteorites to be applied to Mars with confidence. A negative result will perhaps be more exciting in forcing us to look for another object that has been geologically active in the recent past. If the oxygen isotopic composition of Earth and Mars are established to be distinct, accretion theory must provide for different compositions for two planets now separated by only 0.5 AU

  11. Highly Accreting Quasars at High Redshift

    Directory of Open Access Journals (Sweden)

    Mary L. Martínez-Aldama

    2018-01-01

    Full Text Available We present preliminary results of a spectroscopic analysis for a sample of type 1 highly accreting quasars (L/LEdd ~ 1.0 at high redshift, z ~2–3. The quasars were observed with the OSIRIS spectrograph on the GTC 10.4 m telescope located at the Observatorio del Roque de los Muchachos in La Palma. The highly accreting quasars were identified using the 4D Eigenvector 1 formalism, which is able to organize type 1 quasars over a broad range of redshift and luminosity. The kinematic and physical properties of the broad line region have been derived by fitting the profiles of strong UV emission lines such as Aliiiλ1860, Siiii]λ1892 and Ciii]λ1909. The majority of our sources show strong blueshifts in the high-ionization lines and high Eddington ratios which are related with the productions of outflows. The importance of highly accreting quasars goes beyond a detailed understanding of their physics: their extreme Eddington ratio makes them candidates standard candles for cosmological studies.

  12. Synchrotron radiation from spherically accreting black holes

    International Nuclear Information System (INIS)

    Ipser, J.R.; Price, R.H.

    1982-01-01

    Spherical accretion onto a Schwartzchild black hole, of gas with frozen-in magnetic field, is studied numerically and analytically for a range of hole masses and accretion rates in which synchrotron emission is the dominant radiative mechanism. At small radii the equipartition of magnetic, kinetic, and gravitational energy is assumed to apply, and the gas is heated by dissipation of infalling magnetic energy, turbulent energy, etc. The models can be classified into three types: (a) synchrotron cooling negligible, (b) synchrotron cooling important but synchrotron self-absorption negligible, (c) synchrotron cooling and self-absorption important. In the first case gas temperatures become very high near the horizon but luminosity efficiencies (luminosity/mass-energy accretion rate) are low. In cases (b) and (c) the gas flow near the horizon is essentially isothermal and luminosity efficiencies are fairly high. The analysis and results for the isothermal cases (b) and (c) are valid only for moderate dissipative heating and synchrotron self-absorption. If self-absorption is very strong or if dissipated energy is comparable to infall energy, Comptonization effects, not included in the analysis, become important

  13. [Principles of intervertebral disc assessment in private accident insurance].

    Science.gov (United States)

    Steinmetz, M; Dittrich, V; Röser, K

    2015-09-01

    Due to the spread of intervertebral disc degeneration, insurance companies and experts are regularly confronted with related assessments of insured persons under their private accident insurance. These claims pose a particular challenge for experts, since, in addition to the clinical assessment of the facts, extensive knowledge of general accident insurance conditions, case law and current study findings is required. Each case can only be properly assessed through simultaneous consideration of both the medical and legal facts. These guidelines serve as the basis for experts and claims.managers with respect to the appropriate individual factual assessment of intervertebral disc degeneration in private accident insurance.

  14. Heterotopic ossification associated with myelopathy following cervical disc prosthesis implantation.

    Science.gov (United States)

    Wenger, Markus; Markwalder, Thomas-Marc

    2016-04-01

    This case report presents a 37-year-old man with clinical signs of myelopathy almost 9 years after implantation of a Bryan disc prosthesis (Medtronic Sofamor Danek, Memphis, TN, USA) for C5/C6 soft disc herniation. As demonstrated on MRI and CT scan, spinal cord compression was caused by bony spurs due to heterotopic ossification posterior to the still moving prosthesis. The device, as well as the ectopic bone deposits, had to be removed because of myelopathy and its imminent aggravation. Conversion to anterior spondylodesis was performed. Copyright © 2015 Elsevier Ltd. All rights reserved.

  15. The role of zonal flows in disc gravito-turbulence

    Science.gov (United States)

    Vanon, R.

    2018-04-01

    The work presented here focuses on the role of zonal flows in the self-sustenance of gravito-turbulence in accretion discs. The numerical analysis is conducted using a bespoke pseudo-spectral code in fully compressible, non-linear conditions. The disc in question, which is modelled using the shearing sheet approximation, is assumed to be self-gravitating, viscous, and thermally diffusive; a constant cooling timescale is also considered. Zonal flows are found to emerge at the onset of gravito-turbulence and they remain closely linked to the turbulent state. A cycle of zonal flow formation and destruction is established, mediated by a slow mode instability (which allows zonal flows to grow) and a non-axisymmetric instability (which disrupts the zonal flow), which is found to repeat numerous times. It is in fact the disruptive action of the non-axisymmetric instability to form new leading and trailing shearing waves, allowing energy to be extracted from the background flow and ensuring the self-sustenance of the gravito-turbulent regime.

  16. A Novel Combination of Percutaneous Endoscopic Lumbar Discectomy and Epiduroscopic Laser Neural Decompression for Down-migrated Disc Herniation.

    Science.gov (United States)

    Choi, Kyung-Chul; Lee, Dong Chan; Park, Choon-Keun

    2017-05-01

    Although percutaneous endoscopic lumbar discectomy (PELD) is an effective treatment for herniated discs, its application in a disc with extensive migration is still challenging. As such, epiduroscopic laser neural decompression (ELND) provides a new view of the epidural space as well as an alternative treatment for a herniated disc and epidural fibrosis. In this paper the authors introduce the novel combination of PELD and ELND for high grade down-migrated disc herniation.An 87-year old woman presented with severe pain radiating down her leg due to high grade down-migrated disc herniation at L4-5. The therapeutic plan was organized into 3 steps. First, the patient underwent PELD to remove the paracentral extruded disc and open the epidural space between the traversing nerve root and disc space. Second, ELND was performed to remove the down-migrated disc and simultaneously push the free fragment to the L4-5 disc space. Lastly, repetitive free fragments were picked up and streamed upward using ELND. The patient reported significant reduction of pain after surgery. Postoperative magnetic resonance imaging (MRI) showed complete removal of the ruptured disc fragment. A combination of PELD and ELND may be an option of treatments for down-migrated disc herniation.

  17. Quantitative measurement of intervertebral disc signal using MRI

    International Nuclear Information System (INIS)

    Niemelaeinen, R.; Videman, T.; Dhillon, S.S.; Battie, M.C.

    2008-01-01

    Aim: To investigate the spinal cord as an alternative intra-body reference to cerebrospinal fluid (CSF) in evaluating thoracic disc signal intensity. Materials and methods: T2-weighted magnetic resonance imaging (MRI) images of T6-T12 were obtained using 1.5 T machines for a population-based sample of 523 men aged 35-70 years. Quantitative data on the signal intensities were acquired using an image analysis program (SpEx (copy right) ). A random sample of 30 subjects and intraclass correlation coeffcients (ICC) were used to examine the repeatability of the spinal cord measurements. The validity of using the spinal cord as a reference was examined by correlating cord and CSF samples. Finally, thoracic disc signal was validated by correlating it with age without adjustment and adjusting for either cord or CSF. Pearson's r was used for correlational analyses. Results: The repeatability of the spinal cord signal measurements was extremely high (≥0.99). The correlations between the signals of spinal cord and CSF by level were all above 0.9. The spinal cord-adjusted disc signal and age correlated similarly with CSF-adjusted disc signal and age (r = -0.30 to -0.40 versus r = -0.26 to -0.36). Conclusion: Adjacent spinal cord is a good alternative reference to the current reference standard, CSF, for quantitative measurements of disc signal intensity. Clearly fewer levels were excluded when using spinal cord as compared to CSF due to missing reference samples

  18. A New Paradigm for Gamma Ray Bursts: Long Term Accretion Rate Modulation by an External Accretion Disk

    Science.gov (United States)

    Cannizzo, John; Gehrels, Neil

    2009-01-01

    We present a new way of looking at the very long term evolution of GRBs in which the disk of material surrounding the putative black hole powering the GRB jet modulates the mass flow, and hence the efficacy of the process that extracts rotational energy from the black hole and inner accretion disk. The pre-Swift paradigm of achromatic, shallow-to-steep "breaks" in the long term GRB light curves has not been borne out by detailed Swift data amassed in the past several years. We argue that, given the initial existence of a fall-back disk near the progenitor, an unavoidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. The mass reservoir at large radii moves outward with time and gives a natural power law decay to the GRB light curves. In this model, the different canonical power law decay segments in the GRB identified by Zhang et al. and Nousek et al. represent different physical states of the accretion disk. We identify a physical disk state with each power law segment.

  19. Therapeutic surprise! Photodynamic therapy for cavernous haemangioma of the disc

    Directory of Open Access Journals (Sweden)

    Mahesh P Shanmugam

    2017-01-01

    Full Text Available Purpose: To report the response of cavernous haemangioma of the disc to PDT. Methods and Patients: A 32 years old lady presented to us with complaints of sudden onset of blurry vision in her right eye. What seemed initially as polypoidal choroidal vasculopathy turned out as cavernous haemangioma of the disc after pneumatic displacement of the sub-retinal haeme. She was treated with PDT as she was prone to recurrent haemorrhage from the lesion due to her low platelet count. Results: Complete regression of the cavernous haemangioma was noted as early as the second week itself and remained regressed for 4 months. Conclusion: PDT can be safe option for patients presenting with symptomatic cavernous haemangioma of the disc or retina.

  20. Poroelastic behaviour of the degenerating human intervertebral disc: a ten-day study in a loaded disc culture system

    NARCIS (Netherlands)

    Emanuel, K. S.; Vergroesen, P.-P. A.; Peeters, M.; Holewijn, R. M.; Kingma, I.; Smit, T. H.

    2015-01-01

    The intervertebral disc (IVD) allows flexibility to the vertebral column, and transfers the predominant axial loads during daily activities. Its axial biomechanical behaviour is poroelastic, due to the water-binding and releasing capacity of the nucleus pulposus. Degeneration of the intervertebral

  1. Magnetic dynamos in accreting planetary bodies

    Science.gov (United States)

    Golabek, Gregor; Labrosse, Stéphane; Gerya, Taras; Morishima, Ryuji; Tackley, Paul

    2013-04-01

    Laboratory measurements revealed ancient remanent magnetization in meteorites [1] indicating the activity of magnetic dynamos in the corresponding meteorite parent body. To study under which circumstances dynamo activity is possible, we use a new methodology to simulate the internal evolution of a planetary body during accretion and differentiation. Using the N-body code PKDGRAV [2] we simulate the accretion of planetary embryos from an initial annulus of several thousand planetesimals. The growth history of the largest resulting planetary embryo is used as an input for the thermomechanical 2D code I2ELVIS [3]. The thermomechanical model takes recent parametrizations of impact processes [4] and of the magnetic dynamo [5] into account. It was pointed out that impacts can not only deposit heat deep into the target body, which is later buried by ejecta of further impacts [6], but also that impacts expose in the crater region originally deep-seated layers, thus cooling the interior [7]. This combination of impact effects becomes even more important when we consider that planetesimals of all masses contribute to planetary accretion. This leads occasionally to collisions between bodies with large ratios between impactor and target mass. Thus, all these processes can be expected to have a profound effect on the thermal evolution during the epoch of planetary accretion and may have implications for the magnetic dynamo activity. Results show that late-formed planetesimals do not experience silicate melting and avoid thermal alteration, whereas in early-formed bodies accretion and iron core growth occur almost simultaneously and a highly variable magnetic dynamo can operate in the interior of these bodies. [1] Weiss, B.P. et al., Science, 322, 713-716, 2008. [2] Richardson, D. C. et al., Icarus, 143, 45-59, 2000. [3] Gerya, T.V and Yuen, D.J., Phys. Earth Planet. Int., 163, 83-105, 2007. [4] Monteux, J. et al., Geophys. Res. Lett., 34, L24201, 2007. [5] Aubert, J. et al

  2. Numerical modelling of accretion, sintering and differentiation of asteroid 4 Vesta

    Science.gov (United States)

    Neumann, W.; Breuer, D.; Spohn, T.

    2012-09-01

    The Dawn mission provided more precise values of e.g. the mass, the bulk density and the dimensions of the asteroid 4 Vesta. The ground-based observations prior to the mission indicated a dry, basaltic surface composition meaning that the body is differentiated and has been resurfaced by basaltic lava flows. The latter distinguishes Vesta from primordial planetesimals like 21 Lutetia which retained its native surface material (and may still be partially differentiated[1]). The differentiated interior is confirmed by the mass concentration towards the centre of Vesta measured by Dawn. In fact, the core is expected to have 214-226 km in diameter[2]. In the present study numerical calculations of the thermochemical evolution of the asteroid 4 Vesta have been performed adopting the new data obtained by the Dawn mission. We have used the thermal evolution model by [3], which includes accretion (based on the accretion model by [4]), sintering of the accreting porous material due to hot pressing[5], associated changes of the material properties (such as density and thermal conductivity), melting, convective heat transport and differentiation by porous flow of chondritic planetesimals. The heat transport by melt segregation is modeled assuming melt flow in porous media and by supplementing the energy balance equation with additional advection terms. The advection terms for iron and silicate melts are calculated using the Darcy flow equation. This approach is valid for melt fractions large enough such that the melt forms an interconnected network but lower than the rheological critical melt fraction (≈50%). In particular we compare the evolution scenarios arising from the instantaneous (Fig. 1)accretion of Vesta at different formation times t0 (relative to the formation of the calcium-aluminum rich inclusions) with those arising from various noninstantaneous accretion rates. This is important due to the competition between heating in the interior and heat loss through the

  3. Intervertebral disc degeneration : Studies in the loaded disc culture system

    NARCIS (Netherlands)

    Paul, C.P.L.

    2018-01-01

    In dit proefschrift wordt een model beschreven, het Loaded Disc Culture System (LDCS), voor het ex vivo bestuderen van de effecten van mechanische belasting op de tussenwervelschijf. In hoofdstuk 2 laten we zien dat een zekere dosis aan dagelijkse belasting nodig is om de cellen van de

  4. Accretion-driven turbulence in filaments - I. Non-gravitational accretion

    Science.gov (United States)

    Heigl, S.; Burkert, A.; Gritschneder, M.

    2018-03-01

    We study accretion-driven turbulence for different inflow velocities in star-forming filaments using the code RAMSES. Filaments are rarely isolated objects and their gravitational potential will lead to radially dominated accretion. In the non-gravitational case, accretion by itself can already provoke non-isotropic, radially dominated turbulent motions responsible for the complex structure and non-thermal line widths observed in filaments. We find that there is a direct linear relation between the absolute value of the total density-weighted velocity dispersion and the infall velocity. The turbulent velocity dispersion in the filaments is independent of sound speed or any net flow along the filament. We show that the density-weighted velocity dispersion acts as an additional pressure term, supporting the filament in hydrostatic equilibrium. Comparing to observations, we find that the projected non-thermal line width variation is generally subsonic independent of inflow velocity.

  5. Analysis of trace element in intervertebral disc by Atomic Absorption Spectrometry techniques in degenerative disc disease in the Polish population

    Directory of Open Access Journals (Sweden)

    Andrzej Nowakowski

    2015-05-01

    Full Text Available Objective. Although trace elements are regarded crucial and their content has been determined in number of tissue there are only few papers addressing this problem in intervertebral disc in humans. Most of the trace elements are important substrates of enzymes influencing metabolism and senescence process. Others are markers of environmental pollution. Therefore the aim of the research was to analyzed of the trace element content in the intervertebral disc, which may be a vital argument recognizing the background of degenerative changes to be the effect of the environment or metabolic factors. Materials and methods. Material consist of 18 intervertebral disc from 15 patients, acquired in surgical procedure of due to the degenerative disease with Atomic Absorption Spectrometry content of Al, Cd, Co, Pb, Cu, Ni, Mo, Mg, Zn was evaluated. Results. Only 4 of the trace elements were detected in all samples. The correlation analysis showed significant positive age correlation with Al and negative in case of Co. Among elements significant positive correlation was observed between Al/Pb, Co/Mo, Al/Mg, Al/Zn Pb/Zn and Mg/Zn. Negative correlation was observed in Al/Co, Cd/Mg, Co/Mg, Mo/Mg, Co/Zn and Mo/Zn. Conclusions. This study is the first to our knowledge that profiles the elements in intervertebral disc in patients with degenerative changes. We have confirmed significant differences between the trace element contents in intervertebral disc and other tissue. It can be ground for further investigation.

  6. Properties of two-temperature dissipative accretion flow around black holes

    Science.gov (United States)

    Dihingia, Indu K.; Das, Santabrata; Mandal, Samir

    2018-04-01

    We study the properties of two-temperature accretion flow around a non-rotating black hole in presence of various dissipative processes where pseudo-Newtonian potential is adopted to mimic the effect of general relativity. The flow encounters energy loss by means of radiative processes acted on the electrons and at the same time, flow heats up as a consequence of viscous heating effective on ions. We assumed that the flow is exposed with the stochastic magnetic fields that leads to Synchrotron emission of electrons and these emissions are further strengthen by Compton scattering. We obtain the two-temperature global accretion solutions in terms of dissipation parameters, namely, viscosity (α) and accretion rate ({\\dot{m}}), and find for the first time in the literature that such solutions may contain standing shock waves. Solutions of this kind are multitransonic in nature, as they simultaneously pass through both inner critical point (xin) and outer critical point (xout) before crossing the black hole horizon. We calculate the properties of shock-induced global accretion solutions in terms of the flow parameters. We further show that two-temperature shocked accretion flow is not a discrete solution, instead such solution exists for wide range of flow parameters. We identify the effective domain of the parameter space for standing shock and observe that parameter space shrinks as the dissipation is increased. Since the post-shock region is hotter due to the effect of shock compression, it naturally emits hard X-rays, and therefore, the two-temperature shocked accretion solution has the potential to explain the spectral properties of the black hole sources.

  7. A Role of Proto-Accretion Disk Heating Proto-Planets to Evaporation

    Directory of Open Access Journals (Sweden)

    Heon-Young Chang

    2002-09-01

    Full Text Available We study a role of the proto-accretion disk during the formation of the planetary system, which is motivated with recent X-ray observations. There is an observational correlation of the mass of extrasolar planets with their orbital period, which also shows the minimum orbital period. This is insufficiently accounted for by the selection effect alone. Besides, most of planetary formation theories predict the lower limit of semimajor axes of the planetary orbits around 0.01 AU. While the migration theory involving the accretion disk is the most favorable theory, it causes too fast migration and requires the braking mechanism to halt the planet ~ 0.01 AU. The induced gap in the accretion disk due to the planet and/or the truncated disk are desperately required to stop the planet. We explore the planetary evaporation in the accretion disk as another possible scenario to explain the servational lack of massive close-in planets. We calculate the location where the planet is evaporated when the mass and the radius of the planet are given, and find that the evaporation location is approximately proportional to the mass of the planet as mp-1.3 and the radius of the planet as rp1.3. Therefore, we conclude that even the standard cool accretion disk becomes marginally hot to make the small planet evaporate at ~ 0.01 AU. We discuss other auxiliary mechanisms which may provide the accretion disk with extra heats other than the viscous friction, which may consequently make a larger planet evaporate.

  8. Quasi-periodic oscillations from post-shock accretion column of polars

    Science.gov (United States)

    Bera, Prasanta; Bhattacharya, Dipankar

    2018-02-01

    A set of strongly magnetized accreting white dwarfs (polars) shows quasi-periodic oscillations (QPOs) with frequency about a Hz in their optical luminosity. These Hz-frequency QPOs are thought to be generated by intensity variations of the emitted radiation originating at the post-shock accretion column. Thermal instability in the post-shock region, triggered by efficient cooling process at the base, is believed to be the primary reason behind the temporal variability. Here, we study the structure and the dynamical properties of the post-shock accretion column including the effects of bremsstrahlung and cyclotron radiation. We find that the presence of significant cyclotron emission in optical band reduces the overall variability of the post-shock region. In the case of a larger post-shock region above the stellar surface, the effects of stratification due to stellar gravity become important. An accretion column, influenced by the strong gravity, has a smaller variability as the strength of the thermal instability at the base of the column is reduced. On the other hand, the cool, dense plasma, accumulated just above the stellar surface, may enhance the post-shock variability due to the propagation of magnetic perturbations. These characteristics of the post-shock region are consistent with the observed properties of V834 Cen and in general with cataclysmic variable sources that exhibit QPO frequency of about a Hz.

  9. Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles

    Energy Technology Data Exchange (ETDEWEB)

    Chambers, John, E-mail: jchambers@carnegiescience.edu [Carnegie Institution for Science Department of Terrestrial Magnetism, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States)

    2017-11-01

    In the core accretion model, gas-giant planets first form a solid core, which then accretes gas from a protoplanetary disk when the core exceeds a critical mass. Here, we model the atmosphere of a core that grows by accreting ice-rich pebbles. The ice fraction of pebbles evaporates in warm regions of the atmosphere, saturating it with water vapor. Excess water precipitates to lower altitudes. Beneath an outer radiative region, the atmosphere is convective, following a moist adiabat in saturated regions due to water condensation and precipitation. Atmospheric mass, density, and temperature increase with core mass. For nominal model parameters, planets with core masses (ice + rock) between 0.08 and 0.16 Earth masses have surface temperatures between 273 and 647 K and form an ocean. In more massive planets, water exists as a supercritical convecting fluid mixed with gas from the disk. Typically, the core mass reaches a maximum (the critical mass) as a function of the total mass when the core is 2–5 Earth masses. The critical mass depends in a complicated way on pebble size, mass flux, and dust opacity due to the occasional appearance of multiple core-mass maxima. The core mass for an atmosphere of 50% hydrogen and helium may be a more robust indicator of the onset of gas accretion. This mass is typically 1–3 Earth masses for pebbles that are 50% ice by mass, increasing with opacity and pebble flux and decreasing with pebble ice/rock ratio.

  10. Spontaneous regression of an intraspinal disc cyst

    Energy Technology Data Exchange (ETDEWEB)

    Demaerel, P.; Eerens, I.; Wilms, G. [University Hospital, Leuven (Belgium). Dept. of Radiology; Goffin, J. [Dept. of Neurosurgery, University Hospitals, Leuven (Belgium)

    2001-11-01

    We present a patient with a so-called disc cyst. Its location in the ventrolateral epidural space and its communication with the herniated disc are clearly shown. The disc cyst developed rapidly and regressed spontaneously. This observation, which has not been reported until now, appears to support focal degeneration with cyst formation as the pathogenesis. (orig.)

  11. Thermochemical modelling of brown dwarf discs

    NARCIS (Netherlands)

    Greenwood, A. J.; Kamp, I.; Waters, L. B. F. M.; Woitke, P.; Thi, W.-F.; Rab, Ch.; Aresu, G.; Spaans, M.

    The physical properties of brown dwarf discs, in terms of their shapes and sizes, are still largely unexplored by observations. ALMA has by far the best capabilities to observe these discs in sub-mm CO lines and dust continuum, while also spatially resolving some discs. To what extent brown dwarf

  12. 46 CFR 64.61 - Rupture disc.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 2 2010-10-01 2010-10-01 false Rupture disc. 64.61 Section 64.61 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING MARINE PORTABLE TANKS AND CARGO HANDLING SYSTEMS Pressure Relief Devices and Vacuum Relief Devices for MPTs § 64.61 Rupture disc. If a rupture disc...

  13. Novel therapeutic strategies for degenerative disc disease: Review of cell biology and intervertebral disc cell therapy.

    Science.gov (United States)

    Fernandez-Moure, Joseph; Moore, Caitlyn A; Kim, Keemberly; Karim, Azim; Smith, Kevin; Barbosa, Zonia; Van Eps, Jeffrey; Rameshwar, Pranela; Weiner, Bradley

    2018-01-01

    Intervertebral disc degeneration is a disease of the discs connecting adjoining vertebrae in which structural damage leads to loss of disc integrity. Degeneration of the disc can be a normal process of ageing, but can also be precipitated by other factors. Literature has made substantial progress in understanding the biological basis of intervertebral disc, which is reviewed here. Current medical and surgical management strategies have shortcomings that do not lend promise to be effective solutions in the coming years. With advances in understanding the cell biology and characteristics of the intervertebral disc at the molecular and cellular level that have been made, alternative strategies for addressing disc pathology can be discovered. A brief overview of the anatomic, cellular, and molecular structure of the intervertebral disc is provided as well as cellular and molecular pathophysiology surrounding intervertebral disc degeneration. Potential therapeutic strategies involving stem cell, protein, and genetic therapy for intervertebral disc degeneration are further discussed.

  14. Electromagnetic Levitation of a Disc

    Science.gov (United States)

    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…

  15. Intervertebral disc degeneration in dogs

    NARCIS (Netherlands)

    Bergknut, Niklas

    Back pain is common in both dogs and humans, and is often associated with intervertebral disc (IVD) degeneration. The IVDs are essential structures of the spine and degeneration can ultimately result in diseases such as IVD herniation or spinal instability. In order to design new treatments halting

  16. Intervertebral disc degeneration in dogs

    NARCIS (Netherlands)

    Bergknut, N.|info:eu-repo/dai/nl/314418059

    2011-01-01

    Back pain is common in both dogs and humans, and is often associated with intervertebral disc (IVD) degeneration. The IVDs are essential structures of the spine and degeneration can ultimately result in diseases such as IVD herniation or spinal instability. In order to design new treatments halting

  17. Three-dimensional general relativistic radiation magnetohydrodynamical simulation of super-Eddington accretion, using a new code HARMRAD with M1 closure

    Science.gov (United States)

    McKinney, Jonathan C.; Tchekhovskoy, Alexander; Sadowski, Aleksander; Narayan, Ramesh

    2014-07-01

    Black hole (BH) accretion flows and jets are dynamic hot relativistic magnetized plasma flows whose radiative opacity can significantly affect flow structure and behaviour. We describe a numerical scheme, tests, and an astrophysically relevant application using the M1 radiation closure within a new 3D general relativistic radiation magnetohydrodynamics (GRRMHD) massively parallel code called HARMRAD. Our 3D GRRMHD simulation of super-Eddington accretion (about 20 times Eddington) on to a rapidly rotating BH (dimensionless spin j = 0.9375) shows sustained non-axisymmemtric disc turbulence, a persistent electromagnetic jet driven by the Blandford-Znajek effect, a disc wind, and a polar radiation jet. The total accretion efficiency is of the order of 20 per cent, the large-scale electromagnetic jet efficiency is of the order of 10 per cent, the disc wind efficiency is less than 1 per cent, and the total radiative efficiency remains low at only of the order of 1 per cent (of order the Eddington luminosity). However, the radiation jet and the electromagnetic jet both emerge from a geometrically beamed polar region, with super-Eddington isotropic equivalent luminosities. Such simulations with HARMRAD can enlighten the role of BH spin versus discs in launching jets, help determine the origin of spectral and temporal states in X-ray binaries, help to understand how tidal disruption events work, provide an accurate horizon-scale flow structure for M87 and other active galactic nuclei (AGN), and isolate whether AGN feedback is driven by radiation or by an electromagnetic, thermal, or kinetic wind/jet. For example, the low radiative efficiency and weak BH spin-down rate from our simulation suggest that BH growth over cosmological times to billions of solar masses by redshifts of z ˜ 6-8 is achievable even with rapidly rotating BHs and 10 M⊙ BH seeds.

  18. Episodic cauda equina compression from an intradural lumbar herniated disc: a case of 'floppy disc'.

    Science.gov (United States)

    Nagaria, J; Chan, Cc; Kamel, Mh; McEvoy, L; Bolger, C

    2011-09-01

    Intradural disc herniation (IDDH) is a rare complication of intervertebral disc disease and comprises 0.26-0.30% of all herniated discs, with 92% of them located in the lumbar region (1). We present a case of IDDH that presented with intermittent symptoms and signs of cauda equina compression. We were unable to find in the literature, any previously described cases of intermittent cauda equina compression from a herniated intradural disc fragment leading to a "floppy disc syndrome". © JSCR.

  19. Spontaneous Regression of Herniated Lumbar Disc with New Disc Protrusion in the Adjacent Level

    OpenAIRE

    Hakan, Tayfun; G?rcan, Serkan

    2016-01-01

    Spontaneous regression of herniated lumbar discs was reported occasionally. The mechanisms proposed for regression of disc herniation are still incomplete. This paper describes and discusses a case of spontaneous regression of herniated lumbar discs with a new disc protrusion in the adjacent level. A 41-year-old man was admitted with radiating pain and numbness in the left lower extremity with a left posterolateral disc extrusion at L5-S1 level. He was admitted to hospital with low back pain ...

  20. The NEtherlands Cervical Kinematics (NECK) Trial. Cost-effectiveness of anterior cervical discectomy with or without interbody fusion and arthroplasty in the treatment of cervical disc herniation; A double-blind randomised multicenter study

    NARCIS (Netherlands)

    M.P. Arts (Mark); R. Brand (René); B.W. Koes (Bart); W.C. Peul (Wilco); M.E. van den Akker-van Marle (Elske)

    2010-01-01

    textabstractBackground. Patients with cervical radicular syndrome due to disc herniation refractory to conservative treatment are offered surgical treatment. Anterior cervical discectomy is the standard procedure, often in combination with interbody fusion. Accelerated adjacent disc degeneration is

  1. Stress analysis of automotive ventilated disc brake rotor and pads using finite element method

    Directory of Open Access Journals (Sweden)

    A Belhocine

    2016-03-01

    Full Text Available The complexity of the physical or technological systems to be developed or studied led to employing numerical methods based on the principle of an approach as possible nominal solution, but these require large computations requiring efficient computers. The computer code ANSYS also allows the determination and the visualization of the structural deformations due to the contact of slipping between the disc and the pads. The results of the calculations of contact described in this work relate to displacements, Von Mises stress on the disc, contact pressures of the inner and outer pad at various moments of simulation. One precedes then the influence of some parameters on the computation results such as rotation of the disc, the smoothness of the mesh, the material of the brake pads and the friction coefficient enter the disc and the pads, the number of revolutions and the material of the disc, the pads groove.

  2. MR imaging findings of a sequestered disc in the lumbar spine: a comparison with an extruded disc

    Energy Technology Data Exchange (ETDEWEB)

    Sim, Su Youn; Park, Ji Seon; Ryu, Kyung Nam [Kyung Hee University Medical Center, Seoul (Korea, Republic of); Jin, Wook [Kyung Hee University East-west Neo Medical Center, Seoul (Korea, Republic of)

    2007-10-15

    To compare the MR findings of a sequestered disc with an extruded disc. MR images of 28 patients with a sequestered disc and 18 patients with an extruded disc were retrospectively reviewed. Patients with sequestered discs were divided into two groups whether definite separation from the parent disc was or was not seen. In the latter group (definite separation not seen) and the extruded disc group of patients, the signal intensities of the herniated discs were compared with the signal intensities of the parent discs and were evaluated on T1-and T2-weighted images. We also assessed the presence of a notch within the herniated disc. In the sequestered disc group of patients (28 discs), only 5 discs (18%) showed obvious separation from the parent disc. Among the remaining 23 discs with indefinite separation, the notch was visible in 14 discs (61%) and 9 discs (39%) had no notch. In the extruded disc group (18 discs), the notch was visible in 2 (11%) discs and the difference between the two groups was statistically significant ({rho} 0.0002). The signal intensities of the herniated discs on T1-weighted images were isointense in both the sequestered and extruded discs. The difference of incidence of high signal intensities on T2-weighted images was not statistically significant ({rho} = 0.125). It is necessary to consider the possibility of the presence of a sequestered disc when a herniated disc material shows a notch.

  3. MR imaging findings of a sequestered disc in the lumbar spine: a comparison with an extruded disc

    International Nuclear Information System (INIS)

    Sim, Su Youn; Park, Ji Seon; Ryu, Kyung Nam; Jin, Wook

    2007-01-01

    To compare the MR findings of a sequestered disc with an extruded disc. MR images of 28 patients with a sequestered disc and 18 patients with an extruded disc were retrospectively reviewed. Patients with sequestered discs were divided into two groups whether definite separation from the parent disc was or was not seen. In the latter group (definite separation not seen) and the extruded disc group of patients, the signal intensities of the herniated discs were compared with the signal intensities of the parent discs and were evaluated on T1-and T2-weighted images. We also assessed the presence of a notch within the herniated disc. In the sequestered disc group of patients (28 discs), only 5 discs (18%) showed obvious separation from the parent disc. Among the remaining 23 discs with indefinite separation, the notch was visible in 14 discs (61%) and 9 discs (39%) had no notch. In the extruded disc group (18 discs), the notch was visible in 2 (11%) discs and the difference between the two groups was statistically significant (ρ 0.0002). The signal intensities of the herniated discs on T1-weighted images were isointense in both the sequestered and extruded discs. The difference of incidence of high signal intensities on T2-weighted images was not statistically significant (ρ = 0.125). It is necessary to consider the possibility of the presence of a sequestered disc when a herniated disc material shows a notch

  4. Driving of Accretion Disk Variability by the Disk Dynamo

    Science.gov (United States)

    Hogg, J. Drew; Reynolds, Christopher S.

    2016-04-01

    Variability is a ubiquitous feature of emission from accreting objects, but many questions remain as to how the variability is driven and how it relates to the underlying accretion physics. In this talk I will discuss recent results from a long, semi-global MHD simulation of a thin accretion disk around a black hole used to perform a detailed study of the fluctuations in the internal disk stress and the influence these fluctuations have on the accretion flow. In the simulation, low frequency fluctuations of the effective α-parameter in the disk are linked to oscillations of the disk dynamo. These fluctuations in the effective alpha parameter drive “propagating fluctuations” in mass accretion rate through the disk that qualitatively resemble the variability from astrophysical black hole systems. The mass accretion rate has several of the ubiquitous phenomenological properties of black hole variability, including log-normal flux distributions, RMS-flux relationships, and radial coherence.

  5. Quasar emission lines as probes of orientation: implications for disc wind geometries and unification

    Science.gov (United States)

    Matthews, J. H.; Knigge, C.; Long, K. S.

    2017-05-01

    The incidence of broad absorption lines (BALs) in quasar samples is often interpreted in the context of a geometric unification model consisting of an accretion disc and an associated outflow. We use the Sloan Digital Sky Survey quasar sample to test this model by examining the equivalent widths (EWs) of C IV 1550 Å, Mg II 2800 Å, [O III] 5007 Å and C III] 1909 Å. We find that the emission line EW distributions in BAL and non-BAL quasars are remarkably similar - a property that is inconsistent with scenarios in which a BAL outflow rises equatorially from a geometrically thin, optically thick accretion disc. We construct simple models to predict the distributions from various geometries; these models confirm the above finding and disfavour equatorial geometries. We show that obscuration, line anisotropy and general relativistic effects on the disc continuum are unlikely to hide an EW inclination dependence. We carefully examine the radio and polarization properties of BAL quasars. Both suggest that they are most likely viewed (on average) from intermediate inclinations, between type 1 and type 2 active galactic nuclei (AGN). We also find that the low-ionization BAL quasars in our sample are not confined to one region of the 'Eigenvector 1' parameter space. Overall, our work leads to one of the following conclusions, or some combination thereof: (I) the continuum does not emit like a geometrically thin, optically thick disc; (II) BAL quasars are viewed from similar angles to non-BAL quasars, that is, low inclinations and (III) geometric unification does not explain the fraction of BALs in quasar samples.

  6. Disc degeneration: current surgical options

    Directory of Open Access Journals (Sweden)

    C Schizas

    2010-10-01

    Full Text Available Chronic low back pain attributed to lumbar disc degeneration poses a serious challenge to physicians. Surgery may be indicated in selected cases following failure of appropriate conservative treatment. For decades, the only surgical option has been spinal fusion, but its results have been inconsistent. Some prospective trials show superiority over usual conservative measures while others fail to demonstrate its advantages. In an effort to improve results of fusion and to decrease the incidence of adjacent segment degeneration, total disc replacement techniques have been introduced and studied extensively. Short-term results have shown superiority over some fusion techniques. Mid-term results however tend to show that this approach yields results equivalent to those of spinal fusion. Nucleus replacement has gained some popularity initially, but evidence on its efficacy is scarce. Dynamic stabilisation, a technique involving less rigid implants than in spinal fusion and performed without the need for bone grafting, represents another surgical option. Evidence again is lacking on its superiority over other surgical strategies and conservative measures. Insertion of interspinous devices posteriorly, aiming at redistributing loads and relieving pain, has been used as an adjunct to disc removal surgery for disc herniation. To date however, there is no clear evidence on their efficacy. Minimally invasive intradiscal thermocoagulation techniques have also been tried, but evidence of their effectiveness is questioned. Surgery using novel biological solutions may be the future of discogenic pain treatment. Collaboration between clinicians and basic scientists in this multidisciplinary field will undoubtedly shape the future of treating symptomatic disc degeneration.

  7. Zircon dating of oceanic crustal accretion.

    Science.gov (United States)

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

    2009-02-20

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

  8. CT findings of lumbar intervertebral disc: II. Disc herniation (HNP)

    International Nuclear Information System (INIS)

    Yang, W. J.; Lee, J. M.; Bahk, Y. W.

    1984-01-01

    In lumbar region the epidural fat pad is relatively abundant so that CT can provides sufficient information in diagnosis of lumbar HNP. Many authors have reported on the CT findings of HNP such as focal nodular protrusion of the posterior disc margin, obliteration of epidural fat pad, impingement of dural sac and nerve root, swelling of nerve root, soft tissue density in the spinal canal and calcification of disc. However there was so previous report describing incidence and reliability of the findings. It is the purpose of the present study to survey the frequency, reliability, and limitation of these CT findings. The clinical material was consisted of 30 operatively proven cases of HNP of the lumbar spine. Each lumbar CT scan was reviewed retrospectively and the findings were analysed by two radiologists independently. There were 20 males and 10 females and the mean age was 36.7 years. Involvement of L4-S5 level was 2.3 times more frequent than that of L5-S1 level. Of 30 cases, 22 were unilateral posterolateral types and 8 cases central or unilateral far lateral types. CT findings observed were nodular protrusion of the posterior margin of the disc, obliteration of epidural fat pad, impingement of dural sac or nerve root, soft tissue density in the spinal canal and calcification in the posterior portion of the protruded disc, in order of decreasing frequency. The conclusions are follows: 1. Nodular protrusion of the posterior disc margin accompanied by obliteration of epidural fat pad was observed in every case. The former findings was designated as direct sign and the latter indirect. 2. Obliteration of the epidural fat appears to be significant in lateral recesses especially when it occurs unilaterally. This was not true, however, in the centrally located fat pad. 3. Impingement of the dural sac and nerve root were observed in 90% and 67%, respectively, and were very helpful in establishing HNP diagnosis when the direct and indirect signs were equivocal

  9. Study of magnetized accretion flow with cooling processes

    Science.gov (United States)

    Singh, Kuldeep; Chattopadhyay, Indranil

    2018-02-01

    We have studied shock in magnetized accretion flow/funnel flow in case of neutron star with bremsstrahlung cooling and cyclotron cooling. All accretion solutions terminate with a shock close to the neutron star surface, but at some regions of the parameter space, it also harbours a second shock away from the star surface. We have found that cyclotron cooling is necessary for correct accretion solutions which match the surface boundary conditions.

  10. Pulsed Accretion in the T Tauri Binary TWA 3A

    Energy Technology Data Exchange (ETDEWEB)

    Tofflemire, Benjamin M.; Mathieu, Robert D. [Department of Astronomy, University of Wisconsin–Madison, 475 North Charter Street, Madison, WI 53706 (United States); Herczeg, Gregory J. [The Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Akeson, Rachel L.; Ciardi, David R. [NASA Exoplanet Science Institute, IPAC/Caltech, Pasadena, CA 91125 (United States)

    2017-06-20

    TWA 3A is the most recent addition to a small group of young binary systems that both actively accrete from a circumbinary disk and have spectroscopic orbital solutions. As such, it provides a unique opportunity to test binary accretion theory in a well-constrained setting. To examine TWA 3A’s time-variable accretion behavior, we have conducted a two-year, optical photometric monitoring campaign, obtaining dense orbital phase coverage (∼20 observations per orbit) for ∼15 orbital periods. From U -band measurements we derive the time-dependent binary mass accretion rate, finding bursts of accretion near each periastron passage. On average, these enhanced accretion events evolve over orbital phases 0.85 to 1.05, reaching their peak at periastron. The specific accretion rate increases above the quiescent value by a factor of ∼4 on average but the peak can be as high as an order of magnitude in a given orbit. The phase dependence and amplitude of TWA 3A accretion is in good agreement with numerical simulations of binary accretion with similar orbital parameters. In these simulations, periastron accretion bursts are fueled by periodic streams of material from the circumbinary disk that are driven by the binary orbit. We find that TWA 3A’s average accretion behavior is remarkably similar to DQ Tau, another T Tauri binary with similar orbital parameters, but with significantly less variability from orbit to orbit. This is only the second clear case of orbital-phase-dependent accretion in a T Tauri binary.

  11. Concomitant lower thoracic spine disc disease in lumbar spine MR imaging studies.

    Science.gov (United States)

    Arana, Estanislao; Martí-Bonmatí, Luis; Dosdá, Rosa; Mollá, Enrique

    2002-11-01

    Our objective was to study the coexistence of lower thoracic-spine disc changes in patients with low back pain using a large field of view (FOV) in lumbar spine MR imaging. One hundred fifty patients with low back pain were referred to an MR examination. All patients were studied with a large FOV (27 cm), covering from the coccyx to at least the body of T11. Discs were coded as normal, protrusion, and extrusion (either epiphyseal or intervertebral). The relationship between disc disease and level was established with the Pearson chi(2) test. The T11-12 was the most commonly affected level of the lower thoracic spine with 58 disc cases rated as abnormal. Abnormalities of T11-12 and T12-L1 discs were significantly related only to L1-L2 disease ( p=0.001 and p=0.004, respectively) but unrelated to other disc disease, patient's gender, and age. No correlation was found between other discs. Magnetic resonance imaging of the lumbar spine can detect a great amount of lower thoracic disease, although its clinical significance remains unknown. A statistically significant relation was found within the thoracolumbar junctional region (T11-L2), reflecting common pathoanatomical changes. The absence of relation with lower lumbar spine discs is probably due to differences in their pathomechanisms.

  12. Concomitant lower thoracic spine disc disease in lumbar spine MR imaging studies

    International Nuclear Information System (INIS)

    Arana, Estanislao; Marti-Bonmati, Luis; Dosda, Rosa; Molla, Enrique

    2002-01-01

    Our objective was to study the coexistence of lower thoracic-spine disc changes in patients with low back pain using a large field of view (FOV) in lumbar spine MR imaging. One hundred fifty patients with low back pain were referred to an MR examination. All patients were studied with a large FOV (27 cm), covering from the coccyx to at least the body of T11. Discs were coded as normal, protrusion, and extrusion (either epiphyseal or intervertebral). The relationship between disc disease and level was established with the Pearson χ 2 test. The T11-12 was the most commonly affected level of the lower thoracic spine with 58 disc cases rated as abnormal. Abnormalities of T11-12 and T12-L1 discs were significantly related only to L1-L2 disease (p=0.001 and p=0.004, respectively) but unrelated to other disc disease, patient's gender, and age. No correlation was found between other discs. Magnetic resonance imaging of the lumbar spine can detect a great amount of lower thoracic disease, although its clinical significance remains unknown. A statistically significant relation was found within the thoracolumbar junctional region (T11-L2), reflecting common pathoanatomical changes. The absence of relation with lower lumbar spine discs is probably due to differences in their pathomechanisms. (orig.)

  13. Controlled release effervescent buccal discs of buspirone hydrochloride: in vitro and in vivo evaluation studies.

    Science.gov (United States)

    Jaipal, A; Pandey, M M; Charde, S Y; Sadhu, N; Srinivas, A; Prasad, R G

    2016-01-01

    In the present study controlled release effervescent buccal discs of buspirone hydrochloride (BS) were designed using HPMC as rate controlling and bioadhesive polymer by direct compression method. Sodium bicarbonate and citric acid were used in varying amounts as effervescence forming agents. Carbon dioxide evolved due to reaction of sodium bicarbonate and citric acid was explored for its potential as buccal permeation enhancer. The designed buccal discs were evaluated for physical characteristics and in vitro drug release studies. Bioadhesive behavior of designed buccal discs was assessed using texture analyzer. In vivo animal studies were performed in rabbits to study bioavailability of BS in the designed buccal discs and to establish permeation enhancement ability of carbon dioxide. It was observed that effervescent buccal discs have faster drug release compared to non-effervescent buccal discs in vitro and effervescent buccal discs demonstrated significant increase in bioavailability of drug when compared to non-effervescent formulation. Hence, effervescent buccal discs can be used as an alternative to improve the drug permeation resulting in better bioavailability. However, the amount of acid and base used for generation of carbon dioxide should be selected with care as this may damage the integrity of bioadhesive dosage form.

  14. Effects of axial compression and rotation angle on torsional mechanical properties of bovine caudal discs.

    Science.gov (United States)

    Bezci, Semih E; Klineberg, Eric O; O'Connell, Grace D

    2018-01-01

    The intervertebral disc is a complex joint that acts to support and transfer large multidirectional loads, including combinations of compression, tension, bending, and torsion. Direct comparison of disc torsion mechanics across studies has been difficult, due to differences in loading protocols. In particular, the lack of information on the combined effect of multiple parameters, including axial compressive preload and rotation angle, makes it difficult to discern whether disc torsion mechanics are sensitive to the variables used in the test protocol. Thus, the objective of this study was to evaluate compression-torsion mechanical behavior of healthy discs under a wide range of rotation angles. Bovine caudal discs were tested under a range of compressive preloads (150, 300, 600, and 900N) and rotation angles (± 1, 2, 3, 4, or 5°) applied at a rate of 0.5°/s. Torque-rotation data were used to characterize shape changes in the hysteresis loop and to calculate disc torsion mechanics. Torsional mechanical properties were described using multivariate regression models. The rate of change in torsional mechanical properties with compression depended on the maximum rotation angle applied, indicating a strong interaction between compressive stress and maximum rotation angle. The regression models reported here can be used to predict disc torsion mechanics under axial compression for a given disc geometry, compressive preload, and rotation angle. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Concomitant lower thoracic spine disc disease in lumbar spine MR imaging studies

    Energy Technology Data Exchange (ETDEWEB)

    Arana, Estanislao; Marti-Bonmati, Luis; Dosda, Rosa; Molla, Enrique [Department of Radiology, Quiron Clinic, Avd. Blasco Ibanez, 14, 46010 Valencia (Spain)

    2002-11-01

    Our objective was to study the coexistence of lower thoracic-spine disc changes in patients with low back pain using a large field of view (FOV) in lumbar spine MR imaging. One hundred fifty patients with low back pain were referred to an MR examination. All patients were studied with a large FOV (27 cm), covering from the coccyx to at least the body of T11. Discs were coded as normal, protrusion, and extrusion (either epiphyseal or intervertebral). The relationship between disc disease and level was established with the Pearson {chi}{sup 2} test. The T11-12 was the most commonly affected level of the lower thoracic spine with 58 disc cases rated as abnormal. Abnormalities of T11-12 and T12-L1 discs were significantly related only to L1-L2 disease (p=0.001 and p=0.004, respectively) but unrelated to other disc disease, patient's gender, and age. No correlation was found between other discs. Magnetic resonance imaging of the lumbar spine can detect a great amount of lower thoracic disease, although its clinical significance remains unknown. A statistically significant relation was found within the thoracolumbar junctional region (T11-L2), reflecting common pathoanatomical changes. The absence of relation with lower lumbar spine discs is probably due to differences in their pathomechanisms. (orig.)

  16. Uniform and accelerated degradation of pure iron patterned by Pt disc arrays

    Science.gov (United States)

    Huang, Tao; Zheng, Yufeng

    2016-04-01

    Pure iron has been confirmed as a promising biodegradable metal. However, the degradation rate of pure iron should be accelerated to meet the clinical requirements. In this work, two different designs of platinum disc arrays, including sizes of Φ20 μm × S5 μm and Φ4 μm × S4 μm, have been coated on the surface of pure iron. Corrosion tests showed the platinum discs formed plenty of galvanic cells with the iron matrix which significantly accelerated the degradation of pure iron. Simultaneously, due to the designability of the shape, size as well as distribution of Pt discs, the degradation rate as well as degradation uniformity of pure iron can be effectively controlled by coating with platinum discs. The cytotoxicity test results unveiled that Pt discs patterned pure iron exhibited almost no toxicity to human umbilical vein endothelial cells, but a significant inhibition on proliferation of vascular smooth muscle cells. In addition, the hemolysis rate of Pt discs patterned pure iron was lower than 1%. Moreover, Pt discs also effectively reduced the number of adhered platelets. All these results indicated that Pt discs patterning is an effective way to accelerate degradation and improve biocompatibility of pure iron.

  17. Accretion-Ejection Instability in magnetized accretion disk around compact objects

    International Nuclear Information System (INIS)

    Varniere, Peggy

    2002-01-01

    The major problem in accretion physics come from the origin of angular momentum transfer in the disk. My PhD deal with a mechanism (the Accretion-Ejection Instability, AEI) able to explain and link together accretion in the inner region of the disk and ejection. This instability occurs in magnetized accretion disk near equipartition with gas pressure. We first study the impact of some relativistic effects on the instability, particularly on the m = 1 mode. And compared the results with the Quasi-Periodic Oscillation (QPO) observed in micro-quasars. In the second part we study analytically and numerically the Alfven wave emission mechanism which re-emit the angular momentum and energy taken from the inner region of the disk into the corona. The last part deals with MHD numerical simulation. First of all a 2D non-linear disk simulation which contribute to QPO modelization. The last chapter is about a beginning collaboration on 3D simulation in order to study the Alfven wave emission in the corona. (author) [fr

  18. Propagating mass accretion rate fluctuations in black hole X-ray binaries: quantitative tests

    Science.gov (United States)

    Rapisarda, S.; Ingram, A.; van der Klis, M.

    2017-10-01

    Over the past 20 years, a consistent phenomenology has been established to describe the variability properties of Black Hole X-ray Binaries (BHBs). However, the physics behind the observational data is still poorly understood. The recently proposed model PROPFLUC assumes a truncated disc/hot inner flow geometry, with mass accretion rate fluctuations propagating through a precessing inner flow. These two processes give rise respectively to broad band variability and QPO. Because of propagation, the emission from different regions of the disc/hot flow geometry is correlated. In our study we applied the model PROPFLUC on different BHBs (including XTE J1550-564 and Cygnus X-1) in different spectral states, fitting jointly the power spectra in two energy bands and the cross-spectrum between these two bands. This represents the first study to utilize quantitive fitting of a physical model simultaneously to observed power and cross-spectra. For the case of XTE J1550-564, which displays a strong QPO, we found quantitative and qualitative discrepancies between model predictions and data, whereas we find a good fit for the Cygnus X-1 data, which does not display a QPO. We conclude that the discrepancies are generic to the propagating fluctuations paradigm, and may be related to the mechanism originating the QPO.

  19. Factors that influence recurrent lumbar disc herniation.

    Science.gov (United States)

    Yaman, M E; Kazancı, A; Yaman, N D; Baş, F; Ayberk, G

    2017-06-01

    The most common cause of poor outcome following lumbar disc surgery is recurrent herniation. Recurrence has been noted in 5% to 15% of patients with surgically treated primary lumbar disc herniation. There have been many studies designed to determine the risk factors for recurrent lumbar disc herniation. In this study, we retrospectively analysed the influence of disc degeneration, endplate changes, surgical technique, and patient's clinical characteristics on recurrent lumbar disc herniation. Patients who underwent primary single-level L4-L5 lumbar discectomy and who were reoperated on for recurrent L4-L5 disc herniation were retrospectively reviewed. All these operations were performed between August 2004 and September 2009 at the Neurosurgery Department of Ataturk Education and Research Hospital in Ankara, Turkey. During the study period, 126 patients were reviewed, with 101 patients underwent primary single-level L4-L5 lumbar discectomy and 25 patients were reoperated on for recurrent L4-L5 disc herniation. Preoperative higher intervertebral disc height (Pdisc herniation had preoperative higher disc height and higher body mass index. Modic endplate changes had a higher tendency for recurrence of lumbar disc herniation. Well-planned and well-conducted large-scale prospective cohort studies are needed to confirm this and enable convenient treatment modalities to prevent recurrent disc pathology.

  20. OGLE-2014-SN-073 as a fallback accretion powered supernova

    Science.gov (United States)

    Moriya, Takashi J.; Terreran, Giacomo; Blinnikov, Sergei I.

    2018-03-01

    We investigate the possibility that the energetic Type II supernova OGLE-2014-SN-073 is powered by a fallback accretion following the failed explosion of a massive star. Taking massive hydrogen-rich supernova progenitor models, we estimate the fallback accretion rate and calculate the light-curve evolution of supernovae powered by the fallback accretion. We find that such fallback accretion powered models can reproduce the overall observational properties of OGLE-2014-SN-073. It may imply that some failed explosions could be observed as energetic supernovae like OGLE-2014-SN-073 instead of faint supernovae as previously proposed.

  1. ACCRETION DISKS IN TWO-DIMENSIONAL HOYLE-LYTTLETON FLOW

    International Nuclear Information System (INIS)

    Blondin, John M.

    2013-01-01

    We investigate the flip-flop instability observed in two-dimensional planar hydrodynamic simulations of Hoyle-Lyttleton accretion in the case of an accreting object with a radius much smaller than the nominal accretion radius, as one would expect in astrophysically relevant situations. Contrary to previous results with larger accretors, accretion from a homogenous medium onto a small accretor is characterized by a robust, quasi-Keplerian accretion disk. For gas with a ratio of specific heats of 5/3, such a disk remains locked in one direction for a uniform ambient medium. The accretion flow is more variable for gas with a ratio of specific heats of 4/3, with more dynamical interaction of the disk flow with the bow shock leading to occasional flips in the direction of rotation of the accretion disk. In both cases the accretion of angular momentum is determined by the flow pattern behind the accretion shock rather than by the parameters of the upstream flow.

  2. Three-level cervical disc herniation

    Directory of Open Access Journals (Sweden)

    St. Iencean Andrei

    2015-09-01

    Full Text Available Multilevel cervical degenerative disc disease is well known in the cervical spine pathology, with radicular syndromes or cervical myelopathy. One or two level cervical herniated disc is common in adult and multilevel cervical degenerative disc herniation is common in the elderly, with spinal stenosis, and have the same cause: the gradual degeneration of the disc. We report the case of a patient with two level cervical disc herniation (C4 – C5 and C5 – C6 treated by anterior cervical microdiscectomy both levels and fusion at C5 – C6; after five years the patient returned with left C7 radiculopathy and MRI provided the image of a left C6 – C7 disc herniation, he underwent an anterior microsurgical discectomy with rapid relief of symptoms. Three-level cervical herniated disc are rare in adults, and the anterior microdiscectomy with or without fusion solve this pathology.

  3. Migrated herniated disc mimicking a neoplasm.

    Science.gov (United States)

    Hoch, Benjamin; Hermann, George

    2010-12-01

    Disc sequestration is defined as migration of a herniated disc fragment into the epidural space such that it is completely separated from the parent disc. We report a case of a migrated herniated disc that was initially pathologically diagnosed as a cartilage neoplasm. In addition to confounding morphological features, this interpretation may have been influenced by an initial radiological interpretation that did not include herniated disc in the differential diagnosis of a spinal lesion with prominent peripheral contrast enhancement. MR imaging is most helpful in considering other lesions in the differential diagnosis including abscess, hematoma, and primary or metastatic neoplasms. Pathologically, degenerative changes in herniated discs, including clustering of chondrocytes and neovascularization, may be severe resulting in a pseudoneoplastic appearance. Increased awareness of the radiological and pathological features of migrated herniated disc should limit confusion with other tumors.

  4. Retina image–based optic disc segmentation

    Directory of Open Access Journals (Sweden)

    Ching-Lin Wang

    2016-05-01

    Full Text Available The change of optic disc can be used to diagnose many eye diseases, such as glaucoma, diabetic retinopathy and macular degeneration. Moreover, retinal blood vessel pattern is unique for human beings even for identical twins. It is a highly stable pattern in biometric identification. Since optic disc is the beginning of the optic nerve and main blood vessels in retina, it can be used as a reference point of identification. Therefore, optic disc segmentation is an important technique for developing a human identity recognition system and eye disease diagnostic system. This article hence presents an optic disc segmentation method to extract the optic disc from a retina image. The experimental results show that the optic disc segmentation method can give impressive results in segmenting the optic disc from a retina image.

  5. Anterolateral Approach for Central Thoracic Disc Prolapse-Surgical Strategies Used to Tackle Differing Operative Findings: 3-Dimensional Operative Video.

    Science.gov (United States)

    Patel, Krunal; Budohoski, Karol P; Kenyon, Olivia R P; Barone, Damiano G; Santarius, Thomas; Kirollos, Ramez W; Mannion, Richard J; Trivedi, Rikin A

    2018-04-02

    Thoracic disc prolapses causing cord compression can be challenging. For compressive central disc protrusions, a posterior approach is not suitable due to an unacceptable level of cord manipulation. An anterolateral transthoracic approach provides direct access to the disc prolapse allowing for decompression without disturbing the spinal cord. In this video, we describe 2 cases of thoracic myelopathy from a compressive central thoracic disc prolapse. In both cases, informed consent was obtained. Despite similar radiological appearances of heavy calcification, intraoperatively significant differences can be encountered. We demonstrate different surgical strategies depending on the consistency of the disc and the adherence to the thecal sac. With adequate exposure and detachment from adjacent vertebral bodies, soft discs can be, in most instances, separated from the theca with minimal cord manipulation. On the other hand, largely calcified discs often present a significantly greater challenge and require thinning the disc capsule before removal. In cases with significant adherence to dura, in order to prevent cord injury or cerebrospinal fluid leak a thinned shell can be left, providing total detachment from adjacent vertebrae can be achieved. Postoperatively, the first patient, with a significantly calcified disc, developed a transient left leg weakness which recovered by 3-month follow-up. This video outlines the anatomical considerations and operative steps for a transthoracic approach to a central disc prolapse, whilst demonstrating that computed tomography appearances are not always indicative of potential operative difficulties.

  6. NUMERICAL SIMULATION OF ICE ACCRETION ON AIRFOIL

    Directory of Open Access Journals (Sweden)

    Nicusor ALEXANDRESCU

    2009-09-01

    Full Text Available This work consists in the simulation of the ice accretion in the leading edge of aerodynamic profiles and our proposed model encompasses: geometry generation, calculation of the potential flow around the body, boundary layer thickness computation, water droplet trajectory computation, heat and mass balances and the consequent modification of the geometry by the ice growth. The flow calculation is realized with panel methods, using only segments defined over the body contour. The viscous effects are considered using the Karman-Pohlhausen method for the laminar boundary layer. The local heat transfer coefficient is obtained by applying the Smith-Spalding method for the thermal boundary layer. The ice accretion limits and the collection efficiency are determined by computing water droplet trajectories impinging the surface. The heat transfer process is analyzed with an energy and a mass balance in each segment defining the body. Finally, the geometry is modified by the addition of the computed ice thickness to the respective panel. The process by repeating all the steps. The model validation is done using a selection of problems with experimental solution, CIRA (the CESAR project. Hereinafter, results are obtained for different aerodynamic profiles, angles of attack and meteorological parameters

  7. Thick accretion disks around black holes

    International Nuclear Information System (INIS)

    Paczynski, B.

    1982-01-01

    Theory of thick low viscosity disks accreting onto black holes is reviewed. Usefulness of a simplified pseudo-Newtonian potential for studies of disk models is emphasized. It is shown how very high accretion rate leads to a large disk thickness, large pressure gradients in the radial direction, formation of a narrow open funnel around the rotation axis, and a decrease of efficiency of convertion of rest mass into radiation. It is possible that the well collimated powerful radiation beam emerging from the funnel may accelerate some gas to moderately relativistic velocity in a form of a twin jet. The process is not efficient if the funnel is optically thin, but it is hoped that large optical depth of gas in the funnel may increase the fraction of total power coming out as kinetic energy of the jet. This class of models may be applied to SS 433, and possibly to other compact X-ray sources like Sco X-1 and Cyg X-1. These models may be relevant to some active galactic nuclei, but their relatively low efficiency in converting mass to radiation and kinetic energy does not permit too universal application. (orig.)

  8. Ignition of detonation in accreted helium envelopes

    Science.gov (United States)

    Ami Glasner, S.; Livne, E.; Steinberg, E.; Yalinewich, A.; Truran, James W.

    2018-02-01

    Sub Chandrasekhar CO white dwarfs accreting helium have been considered as candidates for SNIa progenitors since the early 1980's (helium shell mass >0.1M⊙). These models, once detonated did not fit the observed spectra and light curve of typical SNIa observations. New theoretical work examined detonations on much less massive (<0.05M⊙) envelopes. They find stable detonations that lead to light curves, spectra and abundances that compare relatively well with the observational data. The exact mechanism leading to the ignition of helium detonation is a key issue, since it is a mandatory first step for the whole scenario. As the flow of the accreted envelope is unstable to convection long before any hydrodynamic phenomena develops, a multidimensional approach is needed in order to study the ignition process. The complex convective reactive flow is challenging to any hydrodynamical solver. According to our best knowledge all previous 2D studies ignited the detonation artificially. We present here, for the first time, fully consistent results from two hydrodynamical 2D solvers that adopt two independent accurate schemes. For both solvers an effort was made to overcome the problematics raised by the finite resolution and numerical diffusion by the advective terms. Our best models lead to the ignition of a detonation in a convective cell. Our results are robust and the agreement between the two different numerical approaches is very good.

  9. The Physics of Wind-Fed Accretion

    International Nuclear Information System (INIS)

    Mauche, Christopher W.; Liedahl, Duane A.; Akiyama, Shizuka; Plewa, Tomasz

    2008-01-01

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

  10. Detection of residual disc hernia material and confirmation of nerve root decompression at lumbar disc herniation surgery by intraoperative ultrasound.

    Science.gov (United States)

    Aoyama, Takeshi; Hida, Kazutoshi; Akino, Minoru; Yano, Shunsuke; Iwasaki, Yoshinobu

    2009-06-01

    The aim of lumbar disc herniation surgery is the removal of herniated disc material (HDM) and complete decompression of the nerve root. As some patients present with residual HDM, we examined the ability of intraoperative ultrasound (IOUS) to detect this material. Between February 2006 and June 2007, we used IOUS in 30 patients undergoing surgery for lumbar disc herniation. They were 17 men and 13 women; their ages ranged from 22 to 63 y (mean 44.0 y). The level surgically addressed was L3/4 in 1, L4/5 in 14 and L5/S1 in 15 patients; they were operated in the prone position. After placing a 3-4 cm midline skin incision, partial hemi-semilaminotomy was performed. HDM was removed through a bone window; a surgical microscope was used during the operation. After removal was judged as adequate, IOUS was performed; 17 patients also underwent IOUS before removal of the herniated disc. For the acquisition of IOUS images, we used LOGIQ 9 and 8c microconvex probes (GE Healthcare, Wauwatosa, WI, USA). The normal anatomical structures were well visualized. HDM was iso- to hyperechoic compared with normal nerve tissue. In three of 17 patients, the dural sac and nerve root could not be distinguished from HDM before removal, although in all 30, the decompressed dural sac, intradural cauda equina and nerve root were well visualized. We posit that the echogenicity of nerve tissue was raised due to compression, rendering it similar to that of the herniated disc. In two patients, IOUS detected residual disc material; the surgical procedure was resumed and sufficient removal was accomplished. IOUS monitoring is safe, convenient and inexpensive. It is also highly useful for the detection of residual HDM and the confirmation of adequate nerve root decompression.

  11. PBH mass growth through radial accretion during the radiation dominated era

    Energy Technology Data Exchange (ETDEWEB)

    Lora-Clavijo, F.D. [Instituto de Astronomía, Universidad Nacional Autónoma de México, AP 70-264, Distrito Federal 04510 (Mexico); Guzmán, F.S.; Cruz-Osorio, A., E-mail: fdlora@astro.unam.mx, E-mail: guzman@ifm.umich.mx, E-mail: alejandro@ifm.umich.mx [Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio C-3, Cd. Universitaria, 58040 Morelia, Michoacán (Mexico)

    2013-12-01

    We model the radial accretion of radiation on Primordial Black Holes (PBH) by numerically solving Einstein's equations coupled to an ultrarelativistic ideal gas with equation of state p = ρ/3. We calculate the final mass of a black hole by the integration of the accreted radiation energy density during the leptonic era between t ∼ 10{sup −4}s to t ∼ 10{sup 2}s after the Big Bang. Our results indicate that small PBHs with initial masses between 10{sup −4} to 1M{sub ⊙} may grow up to hundreds of solar masses, and thus can be SMBH seeds. On the other hand, PBHs formed at t ∼ 1s with initial mass between 900 and ∼ 980M{sub ⊙}, by the time t ∼ 100s show masses of 10{sup 4} to 10{sup 6}M{sub ⊙} which are masses of seeds or already formed SMBHs. The fact that we consider only radial flow implies that our results work well as limiting cases, and it is expected that under more general scenarios the accretion rates may change significantly. Nevertheless we show that it is possible that SMBHs can be PBHs that grew due to the accretion of radiation.

  12. ON THE GRAVITATIONAL STABILITY OF GRAVITO-TURBULENT ACCRETION DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Min-Kai; Kratter, Kaitlin M., E-mail: minkailin@email.arizona.edu [Department of Astronomy and Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2016-06-20

    Low mass, self-gravitating accretion disks admit quasi-steady, “gravito-turbulent” states in which cooling balances turbulent viscous heating. However, numerical simulations show that gravito-turbulence cannot be sustained beyond dynamical timescales when the cooling rate or corresponding turbulent viscosity is too large. The result is disk fragmentation. We motivate and quantify an interpretation of disk fragmentation as the inability to maintain gravito-turbulence due to formal secondary instabilities driven by: (1) cooling, which reduces pressure support; and/or (2) viscosity, which reduces rotational support. We analyze the axisymmetric gravitational stability of viscous, non-adiabatic accretion disks with internal heating, external irradiation, and cooling in the shearing box approximation. We consider parameterized cooling functions in 2D and 3D disks, as well as radiative diffusion in 3D. We show that generally there is no critical cooling rate/viscosity below which the disk is formally stable, although interesting limits appear for unstable modes with lengthscales on the order of the disk thickness. We apply this new linear theory to protoplanetary disks subject to gravito-turbulence modeled as an effective viscosity, and cooling regulated by dust opacity. We find that viscosity renders the disk beyond ∼60 au dynamically unstable on radial lengthscales a few times the local disk thickness. This is coincident with the empirical condition for disk fragmentation based on a maximum sustainable stress. We suggest turbulent stresses can play an active role in realistic disk fragmentation by removing rotational stabilization against self-gravity, and that the observed transition in behavior from gravito-turbulent to fragmenting may reflect instability of the gravito-turbulent state itself.

  13. The PANDA Endcap Disc DIRC

    Science.gov (United States)

    Föhl, K.; Ali, A.; Belias, A.; Dzhygadlo, R.; Gerhardt, A.; Götzen, K.; Kalicy, G.; Krebs, M.; Lehmann, D.; Nerling, F.; Patsyuk, M.; Peters, K.; Schepers, G.; Schmitt, L.; Schwarz, C.; Schwiening, J.; Traxler, M.; Böhm, M.; Eyrich, W.; Lehmann, A.; Pfaffinger, M.; Uhlig, F.; Düren, M.; Etzelmüller, E.; Hayrapetyan, A.; Kreutzfeld, K.; Merle, O.; Rieke, J.; Schmidt, M.; Wasem, T.; Achenbach, P.; Cardinali, M.; Hoek, M.; Lauth, W.; Schlimme, S.; Sfienti, C.; Thiel, M.

    2018-02-01

    Positively identifying charged kaons in the PANDA forward endcap solid angle range can be achieved with the Endcap Disc DIRC, allowing kaon-pion separation from 1 up to 4 GeV/c with a separation power of at least 3 standard deviations. Design, performance, and components of this DIRC are given, including the recently introduced TOFPET-ASIC based read-out. Results of a prototype operated in a test beam at DESY in 2016 are shown.

  14. Upper thoracic-spine disc degeneration in patients with cervical pain.

    Science.gov (United States)

    Arana, Estanislao; Martí-Bonmatí, Luis; Mollá, Enrique; Costa, Salvador

    2004-01-01

    To study the relationship of upper thoracic spine degenerative disc contour changes on MR imaging in patients with neck pain. The relation between upper thoracic and cervical spine degenerative disc disease is not well established. One hundred and fifty-six patients referred with cervical pain were studied. There were 73 women and 77 men with a mean age of 48.6 +/- 14.6 years (range, 19 to 83 years). All MR studies were performed with a large 23-cm FOV covering at least from the body of T4 to the clivus. Discs were coded as normal, protrusion/bulge or extrusion. Degenerative thoracic disc contour changes were observed in 13.4% of patients with cervical pain. T2-3 was the most commonly affected level of the upper thoracic spine, with 15 bulge/protrusions and one extrusion. Upper degenerative thoracic disc contour changes presented in older patients than the cervical levels (Student-Newman-Keuls test, P < 0.001). Degenerative disc contour changes at the C7-T1, T1-2, T2-3 and T3-4 levels were significantly correlated ( P = 0.001), but unrelated to any other disc disease, patient's gender or age. Degenerative cervical disc disease was closely related together ( P < 0.001), but not with any thoracic disc. A statistically significant relation was found within the upper thoracic discs, reflecting common pathoanatomical changes. The absence of relation to cervical segments is probably due to differences in their pathomechanisms.

  15. Upper thoracic-spine disc degeneration in patients with cervical pain

    Energy Technology Data Exchange (ETDEWEB)

    Arana, Estanislao; Marti-Bonmati, Luis; Costa, Salvador [Department of Radiology, Clinica Quiron, Avda Blasco Ibanez 14, 46010, Valencia (Spain); Molla, Enrique [Department of Radiology, Clinica Quiron, Avda Blasco Ibanez 14, 46010, Valencia (Spain); Department of Morphological Sciences, University of Valencia, Valencia (Spain)

    2004-01-01

    To study the relationship of upper thoracic spine degenerative disc contour changes on MR imaging in patients with neck pain. The relation between upper thoracic and cervical spine degenerative disc disease is not well established. One hundred and fifty-six patients referred with cervical pain were studied. There were 73 women and 77 men with a mean age of 48.6{+-}14.6 years (range, 19 to 83 years). All MR studies were performed with a large 23-cm FOV covering at least from the body of T4 to the clivus. Discs were coded as normal, protrusion/bulge or extrusion. Degenerative thoracic disc contour changes were observed in 13.4% of patients with cervical pain. T2-3 was the most commonly affected level of the upper thoracic spine, with 15 bulge/protrusions and one extrusion. Upper degenerative thoracic disc contour changes presented in older patients than the cervical levels (Student-Newman-Keuls test, P<0.001). Degenerative disc contour changes at the C7-T1, T1-2, T2-3 and T3-4 levels were significantly correlated (P=0.001), but unrelated to any other disc disease, patient's gender or age. Degenerative cervical disc disease was closely related together (P<0.001), but not with any thoracic disc. A statistically significant relation was found within the upper thoracic discs, reflecting common pathoanatomical changes. The absence of relation to cervical segments is probably due to differences in their pathomechanisms. (orig.)

  16. Upper thoracic-spine disc degeneration in patients with cervical pain

    International Nuclear Information System (INIS)

    Arana, Estanislao; Marti-Bonmati, Luis; Costa, Salvador; Molla, Enrique

    2004-01-01

    To study the relationship of upper thoracic spine degenerative disc contour changes on MR imaging in patients with neck pain. The relation between upper thoracic and cervical spine degenerative disc disease is not well established. One hundred and fifty-six patients referred with cervical pain were studied. There were 73 women and 77 men with a mean age of 48.6±14.6 years (range, 19 to 83 years). All MR studies were performed with a large 23-cm FOV covering at least from the body of T4 to the clivus. Discs were coded as normal, protrusion/bulge or extrusion. Degenerative thoracic disc contour changes were observed in 13.4% of patients with cervical pain. T2-3 was the most commonly affected level of the upper thoracic spine, with 15 bulge/protrusions and one extrusion. Upper degenerative thoracic disc contour changes presented in older patients than the cervical levels (Student-Newman-Keuls test, P<0.001). Degenerative disc contour changes at the C7-T1, T1-2, T2-3 and T3-4 levels were significantly correlated (P=0.001), but unrelated to any other disc disease, patient's gender or age. Degenerative cervical disc disease was closely related together (P<0.001), but not with any thoracic disc. A statistically significant relation was found within the upper thoracic discs, reflecting common pathoanatomical changes. The absence of relation to cervical segments is probably due to differences in their pathomechanisms. (orig.)

  17. Aerodynamic Simulation of Runback Ice Accretion

    Science.gov (United States)

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

    2010-01-01

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

  18. Spinning up black holes with super-critical accretion flows

    Czech Academy of Sciences Publication Activity Database

    Sądowski, A.; Bursa, Michal; Abramowicz, M. A.; Kluzniak, W.; Lasota, J.-P.; Moderski, R.; Safarzadeh, M.

    2011-01-01

    Roč. 532, August (2011), A41/1-A41/11 ISSN 0004-6361 Institutional research plan: CEZ:AV0Z10030501 Keywords : black hole physics * accretion * accretion disks Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.587, year: 2011

  19. Understanding the Emission Region Geometry in Weakly Accreting Black Holes

    NARCIS (Netherlands)

    Markoff, S.; Maitra, D.; van Oers, P.; Brocksopp, C.; Corbel, S.; Gallo, E.; Homan, J.; Migliari, S.; Nowak, M.; Tomsick, J.; Wilms, J.

    2007-01-01

    In the last several years, multiwavelength monitoring programs have allowed us to develop a general description of the observational characteristics of accreting black holes as they journey through their outburst cycles. Driven seemingly to a large extent by the accretion rate, these sources display

  20. Stochastic Resonance of Accretion Disk and the Persistent Low ...

    Indian Academy of Sciences (India)

    oscillation of accretion disk. Therefore, in this paper, based on the research of. Titarchuk & Osherovich (2000), we have calculated the PSD of vertical oscillat- ing luminosity of accretion disk subject to viscidity force and a white noise type stochastic force, and discussed in detail the SR phenomenon of PSD and proposed an.

  1. Dead Zone Accretion Flows in Protostellar Disks

    Science.gov (United States)

    Turner, Neal; Sano, T.

    2008-01-01

    Planets form inside protostellar disks in a dead zone where the electrical resistivity of the gas is too high for magnetic forces to drive turbulence. We show that much of the dead zone nevertheless is active and flows toward the star while smooth, large-scale magnetic fields transfer the orbital angular momentum radially outward. Stellar X-ray and radionuclide ionization sustain a weak coupling of the dead zone gas to the magnetic fields, despite the rapid recombination of free charges on dust grains. Net radial magnetic fields are generated in the magnetorotational turbulence in the electrically conducting top and bottom surface layers of the disk, and reach the midplane by ohmic diffusion. A toroidal component to the fields is produced near the midplane by the orbital shear. The process is similar to the magnetization of the solar tachocline. The result is a laminar, magnetically driven accretion flow in the region where the planets form.

  2. Observational constraints on black hole accretion disks

    Science.gov (United States)

    Liang, Edison P.

    1994-01-01

    We review the empirical constraints on accretion disk models of stellar-mass black holes based on recent multiwavelength observational results. In addition to time-averaged emission spectra, the time evolutions of the intensity and spectrum provide critical information about the structure, stability, and dynamics of the disk. Using the basic thermal Keplerian disk paradigm, we consider in particular generalizations of the standard optically thin disk models needed to accommodate the extremely rich variety of dynamical phenomena exhibited by black hole candidates ranging from flares of electron-positron annihilations and quasiperiodic oscillations in the X-ray intensity to X-ray novae activity. These in turn provide probes of the disk structure and global geometry. The goal is to construct a single unified framework to interpret a large variety of black hole phenomena. This paper will concentrate on the interface between basic theory and observational data modeling.

  3. Pre-main-sequence disk accretion in Z Canis Majoris

    International Nuclear Information System (INIS)

    Hartmann, L.; Kenyon, S.J.; Hewett, R.; Edwards, S.; Strom, K.M.; Strom, S.E.; Stauffer, J.R.

    1989-01-01

    It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion. 41 references

  4. Pre-main-sequence disk accretion in Z Canis Majoris

    Science.gov (United States)

    Hartmann, L.; Kenyon, S. J.; Hewett, R.; Edwards, S.; Strom, K. M.; Strom, S. E.; Stauffer, J. R.

    1989-01-01

    It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion.

  5. Intradiscal injection of oxygen-ozone gas mixture for the treatment of cervical disc herniations.

    Science.gov (United States)

    Alexandre, A; Corò, L; Azuelos, A; Buric, J; Salgado, H; Murga, M; Marin, F; Giocoli, H

    2005-01-01

    For disc herniations the use of open surgical approaches is reduced since new percutaneous methods allowing shrinkage of the disc and improvement of the radicular function are gaining interest. Studies on the spontaneous disappearance of disc fragments have demonstrated autoimmune responses with a chronic inflammatory reaction. Also radicular pain has been shown to be mostly due to biochemical mechanisms. Researchers in different fields surprisingly noticed that a brief, calculated, oxidative stress by ozone administration may correct a persistent imbalance due to excessive, chronic oxidative injury. Oxygen-ozone gas injection in painful patients has a dramatic effect on clinical symptoms. On these bases the intradiscal injection of oxygen-ozone gas has been conceived. We report the treatment on a series of patients affected by cervical disc pathology, treated by intradiscal injection of oxygen-ozone gas mixture. The effects both on pain and on radicular dysfunction are impressive. The morphological effect of the treatment was also evaluated by pathological examination.

  6. Testing Models of Circum-Binary-AGN Accretion for PSO J334.2028+01.4075

    Science.gov (United States)

    Foord, Adi; Gultekin, Kayhan; Reynolds, Mark

    2017-08-01

    We present analysis of new Chandra data of PSO J334.2028+01.4075 (PSO J334 hereafter), a strong binary AGN candidate discovered by Liu et al. (2015) based on periodic variation of the optical flux. Recent radio coverage presented in Mooley et al. (2017) further supports that PSO J334 is a binary black hole system, as the quasar was found to be lobe-dominated with a twisted radio structure, possibly due to a precessing jet. With no prior X-ray coverage for PSO J334, our new 50 ksec Chandra observation allows for the unique opportunity to differentiate between a single or binary-AGN system, and if a binary, can characterize the mode of accretion. The two most basic sets of predictions via simulations of circum-binary accretion model are a “cavity”, where the inner region of the accretion disk is mostly empty and emission is truncated blueward of the wavelength associated with the temperature of the innermost ring, or “minidisks”, where there is substantial accretion onto one or both of the members of the binary, each with their own shock-heated thin-disk accretion system. We find the X-ray emission to be well-fit with a heavily absorbed power-law, incompatible with the cavity scenario. Further, we construct an SED of PSO J334 by combining radio through X-ray observations and compare it to standard QSO SEDs. We discuss the implications of the comparison between the SED of PSO J334 and that of a single AGN, and assess the likelihood of the binary model for PSO J334.

  7. Studying the accretion geometry of EXO 2030+375 at luminosities close to the propeller regime

    Science.gov (United States)

    Fürst, F.; Kretschmar, P.; Kajava, J. J. E.; Alfonso-Garzón, J.; Kühnel, M.; Sanchez-Fernandez, C.; Blay, P.; Wilson-Hodge, C. A.; Jenke, P.; Kreykenbohm, I.; Pottschmidt, K.; Wilms, J.; Rothschild, R. E.

    2017-10-01

    The Be X-ray binary EXO 2030+375was in an extended low-luminosity state during most of 2016. We observed this state with NuSTARand Swift, supported by INTEGRALobservations and optical spectroscopy with the Nordic Optical Telescope (NOT). We present a comprehensive spectral and timing analysis of these data here to study the accretion geometry and investigate a possible onset of the propeller effect. The Hα data show that the circumstellar disk of the Be-star is still present. We measure equivalent widths similar to values found during more active phases in the past, indicating that the low-luminosity state is not simply triggered by a smaller Be disk. The NuSTARdata, taken at a 3-78 keV luminosity of 6.8 × 1035 erg s-1 (for a distance of 7.1 kpc), are nicely described by standard accreting pulsar models such as an absorbed power law with a high-energy cutoff. We find that pulsations are still clearly visible at these luminosities, indicating that accretion is continuing despite the very low mass transfer rate. In phase-resolved spectroscopy we find a peculiar variation of the photon index from 1.5 to 2.5 over only about 3% of the rotational period. This variation is similar to that observed with XMM-Newtonat much higher luminosities. It may be connected to the accretion column passing through our line of sight. With Swift/XRT we observe luminosities as low as 1034 erg s-1 where the data quality did not allow us to search for pulsations, but the spectrum is much softer and well described by either a blackbody or soft power-law continuum. This softer spectrum might be due to the accretion being stopped by the propeller effect and we only observe the neutron star surface cooling.

  8. Truncation of the Inner Accretion Disk Around a Black Hole at Low Luminosity

    Science.gov (United States)

    Tomsick, John A.; Yamoka, Kazutaka; Corbel, Stephane; Kaaret, Philip; Kalemci, Emrah; Migliari, Simone

    2011-01-01

    Most black hole binaries show large changes in X-ray luminosity caused primarily by variations in mass accretion rate. An important question for understanding black hole accretion and jet production is whether the inner edge of the accretion disk recedes at low accretion rate. Measurements of the location of the inner edge (R(sub in)) can be made using iron emission lines that arise due to fluorescence of iron in the disk, and these indicate that R(sub in) is very close to the black hole at high and moderate luminosities (greater than or equal to 1% of the Eddington luminosity, L(sub Edd). Here, we report on X-ray observations of the black hole GX 339-4 in the hard state by Suzaku and the Rossi X-ray Timing Explorer that extend iron line studies to 0.14% L(sub Edd) and show that R(sub in) increases by a factor of greater than 27 over the value found when GX 339-4 was bright. The exact value of R(sub in) depends on the inclination of the inner disk (i), and we derive 90% confidence limits of R(sub in) greater than 35 R(sub g) at i = 0 degrees and R(sub in) greater than 175 R(sub g) at i = 30 degrees. This provides direct evidence that the inner portion of the disk is not present at low luminosity, allowing for the possibility that the inner disk is replaced by advection- or magnetically dominated accretion flows.

  9. Modified viscosity in accretion disks. Application to Galactic black hole binaries, intermediate mass black holes, and active galactic nuclei

    Science.gov (United States)

    Grzędzielski, Mikołaj; Janiuk, Agnieszka; Czerny, Bożena; Wu, Qingwen

    2017-07-01

    Aims: Black holes (BHs) surrounded by accretion disks are present in the Universe at different scales of masses, from microquasars up to the active galactic nuclei (AGNs). Since the work of Shakura & Sunyaev (1973, A&A, 24, 337) and their α-disk model, various prescriptions for the heat-production rate are used to describe the accretion process. The current picture remains ad hoc due the complexity of the magnetic field action. In addition, accretion disks at high Eddington rates can be radiation-pressure dominated and, according to some of the heating prescriptions, thermally unstable. The observational verification of their resulting variability patterns may shed light on both the role of radiation pressure and magnetic fields in the accretion process. Methods: We compute the structure and time evolution of an accretion disk, using the code GLADIS (which models the global accretion disk instability). We supplement this model with a modified viscosity prescription, which can to some extent describe the magnetisation of the disk. We study the results for a large grid of models, to cover the whole parameter space, and we derive conclusions separately for different scales of black hole masses, which are characteristic for various types of cosmic sources. We show the dependencies between the flare or outburst duration, its amplitude, and period, on the accretion rate and viscosity scaling. Results: We present the results for the three grids of models, designed for different black hole systems (X-ray binaries, intermediate mass black holes, and galaxy centres). We show that if the heating rate in the accretion disk grows more rapidly with the total pressure and temperature, the instability results in longer and sharper flares. In general, we confirm that the disks around the supermassive black holes are more radiation-pressure dominated and present relatively brighter bursts. Our method can also be used as an independent tool for the black hole mass determination

  10. Testing Convergence for Global Accretion Disks

    Science.gov (United States)

    Hawley, John F.; Richers, Sherwood A.; Guan, Xiaoyue; Krolik, Julian H.

    2013-08-01

    Global disk simulations provide a powerful tool for investigating accretion and the underlying magnetohydrodynamic turbulence driven by magneto-rotational instability (MRI). Using them to accurately predict quantities such as stress, accretion rate, and surface brightness profile requires that purely numerical effects, arising from both resolution and algorithm, be understood and controlled. We use the flux-conservative Athena code to conduct a series of experiments on disks having a variety of magnetic topologies to determine what constitutes adequate resolution. We develop and apply several resolution metrics: langQz rang and langQ phirang, the ratio of the grid zone size to the characteristic MRI wavelength, αmag, the ratio of the Maxwell stress to the magnetic pressure, and \\langle B_R^2\\rangle /\\langle B_\\phi ^2\\rangle, the ratio of radial to toroidal magnetic field energy. For the initial conditions considered here, adequate resolution is characterized by langQz rang >= 15, langQ phirang >= 20, αmag ≈ 0.45, and \\langle B_R^2\\rangle /\\langle B_\\phi ^2\\rangle \\approx 0.2. These values are associated with >=35 zones per scaleheight H, a result consistent with shearing box simulations. Numerical algorithm is also important. Use of the Harten-Lax-van Leer-Einfeldt flux solver or second-order interpolation can significantly degrade the effective resolution compared to the Harten-Lax-van Leer discontinuities flux solver and third-order interpolation. Resolution at this standard can be achieved only with large numbers of grid zones, arranged in a fashion that matches the symmetries of the problem and the scientific goals of the simulation. Without it, however, quantitative measures important to predictions of observables are subject to large systematic errors.

  11. Optic Disc Identification Methods for Retinal Images

    Directory of Open Access Journals (Sweden)

    Florin Rotaru

    2014-07-01

    Full Text Available Presented are the methods proposed by authors to identify and model the optic disc in colour retinal images. The first three our approaches localized the optic disc in two steps: a in the green component of RGB image the optic disc area is detected based on texture indicators and pixel intensity variance analysis; b on the segmented area the optic disc edges are extracted and the resulted boundary is approximated by a Hough transform. The last implemented method identifies the optic disc area by analysis of blood vessels network extracted in the green channel of the original image. In the segmented area the optic disc edges are obtained by an iterative Canny algorithm and are approximated by a circle Hough transform.

  12. Biomaterials for intervertebral disc regeneration and repair.

    Science.gov (United States)

    Bowles, Robert D; Setton, Lori A

    2017-06-01

    The intervertebral disc contributes to motion, weight bearing, and flexibility of the spine, but is susceptible to damage and morphological changes that contribute to pathology with age and injury. Engineering strategies that rely upon synthetic materials or composite implants that do not interface with the biological components of the disc have not met with widespread use or desirable outcomes in the treatment of intervertebral disc pathology. Here we review bioengineering advances to treat disc disorders, using cell-supplemented materials, or acellular, biologically based materials, that provide opportunity for cell-material interactions and remodeling in the treatment of intervertebral disc disorders. While a field still in early development, bioengineering-based strategies employing novel biomaterials are emerging as promising alternatives for clinical treatment of intervertebral disc disorders. Copyright © 2017 Elsevier Ltd. All rights reserved.

  13. Investigation of accretion formation in a blast furnace shaft

    Energy Technology Data Exchange (ETDEWEB)

    Klima, R.; Hoefer, O.; Chiarotti, U.; Fredman, T.; Hillmann, C.; Raipala, K.; Eriksson, J. (eds.) [BFI Duesseldorf (Germany)

    2005-07-01

    Accretions in the bosh, belly and shaft have a significant influence on blast furnace performance and on the service life of the refractory lining and the cooling system. To analyse the mechanisms of formation and dislodging of accretions, investigations were carried out at four different blast furnaces. Three blast furnaces were equipped with additional measurements to investigate the accretion formation process and to provide information for the development of accretion estimation models. Installation activities included thermocouples, heat-flux meters, staves with instrumentation for heat-flux measurement and a small horizontal lance. The distribution of accretions in the shaft was documented. Samples were taken out of accretions during blast furnace stoppages. Their acquisition was simplified with newly developed sampling devices. The samples were analysed to determine chemical and mineralogical properties and thermal conductivity. Samples were mainly made up of reduced iron or of coke and sinter structures glued together by zinc or alkali compounds. Together with a newly developed offline model for the simulation of accretion formation, different parameters influencing the formation process were identified. The main parameters are: burden material composition, blast furnace operating conditions; and the cooling system. Countermeasures to prevent excessive accretion growth were determined. They offer a better operational control of accretions. Different models to identify accretion formation were developed and an overview was presented. Different models were necessary to distinguish between the various measurement, cooling-system and blast-furnace setups. Most of the models are already implemented and in operational use. For some of them application at other blast furnaces was already realised or is possible. 9 refs., 18 figs., 20 tab.

  14. Eccentricity evolution during planet-disc interaction

    Science.gov (United States)

    Ragusa, Enrico; Rosotti, Giovanni; Teyssandier, Jean; Booth, Richard; Clarke, Cathie J.; Lodato, Giuseppe

    2018-03-01

    During the process of planet formation, the planet-disc interactions might excite (or damp) the orbital eccentricity of the planet. In this paper, we present two long (t ˜ 3 × 105 orbits) numerical simulations: (a) one (with a relatively light disc, Md/Mp = 0.2), where the eccentricity initially stalls before growing at later times and (b) one (with a more massive disc, Md/Mp = 0.65) with fast growth and a late decrease of the eccentricity. We recover the well-known result that a more massive disc promotes a faster initial growth of the planet eccentricity. However, at late times the planet eccentricity decreases in the massive disc case, but increases in the light disc case. Both simulations show periodic eccentricity oscillations superimposed on a growing/decreasing trend and a rapid transition between fast and slow pericentre precession. The peculiar and contrasting evolution of the eccentricity of both planet and disc in the two simulations can be understood by invoking a simple toy model where the disc is treated as a second point-like gravitating body, subject to secular planet-planet interaction and eccentricity pumping/damping provided by the disc. We show how the counterintuitive result that the more massive simulation produces a lower planet eccentricity at late times can be understood in terms of the different ratios of the disc-to-planet angular momentum in the two simulations. In our interpretation, at late times the planet eccentricity can increase more in low-mass discs rather than in high-mass discs, contrary to previous claims in the literature.

  15. Enhancing the rate of tidal disruptions of stars by a self-gravitating disc around a massive central black hole

    Directory of Open Access Journals (Sweden)

    Šubr L.

    2012-12-01

    Full Text Available We further study the idea that a self-gravitating accretion disc around a supermassive black hole can increase the rate of gradual orbital decay of stellar trajectories (and hence tidal disruption events by setting some stars on eccentric trajectories. Cooperation between the gravitational field of the disc and the dissipative environment can provide a mechanism explaining the origin of stars that become bound tightly to the central black hole. We examine this process as a function of the black hole mass and conclude that it is most efficient for intermediate central masses of the order of ∼ 104Mʘ. Members of the cluster experience the stage of orbital decay via collisions with an accretion disc and by other dissipative processes, such as tidal effects, dynamical friction and the emission of gravitational waves. Our attention is concentrated on the region of gravitational dominance of the central body. Mutual interaction between stars and the surrounding environment establishes a non-spherical shape and anisotropy of the nuclear cluster. In some cases, the stellar sub-system acquires ring-type geometry. Stars of the nuclear cluster undergo a tidal disruption event as they plunge below the tidal radius of the supermassive black hole.

  16. Intradural cervical disc herniation: a case report

    Energy Technology Data Exchange (ETDEWEB)

    Chung, Seung Eun; Lee, Sang Ho; Jo, Byung June; Yoon, Deug Hee [Wooridul Spine Hospital, Seoul (Korea, Republic of); Kim, Tae Hong [Inje University College of Medicine, Inje (Korea, Republic of)

    2005-07-15

    Intradural cervical disc herniation is an extremely rare condition and its pathogenesis is not certain. We experienced a case of intradural cervical disc herniation at the C4-5 level in a 56-year-old man. The preoperative sagittal T1- and T2- weighted images revealed an intradural iso-intensity lesion, with the spinal cord behind the posterior longitudinal ligament at the C4-5 disc level. The post-contrast T1-weighted image revealed a peripheral enhanced intradural lesion. We report here on a case of an intradural cervical disc herniation that was diagnosed by radiological examination, and we include a review of the related literature.

  17. Computed tomography in lumbar herniated disc

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Chul Soon; Chang, Kee Hyun; Han, Man Chung [Seoul National University College of Medicine, Seoul (Korea, Republic of)

    1984-09-15

    197 spine CTs were performed from 29th , March 1982 to 7th March, 1984. Among them, 39 patients preoperatively diagnosed as herniated nucleus pulposus or bulging disc with CT and myelography were operated. 43 disc spaces of disc disease are analysed in true positive and false negative cases. Finally the accuracy, sensitivity and specificity of spine CT and myelography are calculated. The results are as follows: 1. The CT findings of disc diseases are in order of frequency, asymmetrical obliteration of epidural fat (82%) , ventral indentation or compression on dural sac (72%), focal protrusion of disc (64%), root changes - obliteration, displacement, compression, non-filling of metrizamide - (54%), diffuse disc bulging (36%), disc at body level (31%), disc calcifications (26%), disc vacuum (10%) and other associated findings - spinal stenosis, foraminal stenosis, ligament flavum thickening, facet joint hypertrophy (26%). 2. Sensitivities of spine CT and myelography are 95% and 94%, specificities are 67%, 50% and overall accuracies 93%, 87%, respectively. 3. Therefore, it is recommended that the spine CT be used as a primary diagnostic method and the myelography as a secondary complementary study when the CT gives no conclusive findings.

  18. Debris disc constraints on planetesimal formation

    Science.gov (United States)

    Krivov, Alexander V.; Ide, Aljoscha; Löhne, Torsten; Johansen, Anders; Blum, Jürgen

    2018-02-01

    Two basic routes for planetesimal formation have been proposed over the last decades. One is a classical `slow-growth' scenario. Another one is particle concentration models, in which small pebbles are concentrated locally and then collapse gravitationally to form planetesimals. Both types of models make certain predictions for the size spectrum and internal structure of newly born planetesimals. We use these predictions as input to simulate collisional evolution of debris discs left after the gas dispersal. The debris disc emission as a function of a system's age computed in these simulations is compared with several Spitzer and Herschel debris disc surveys around A-type stars. We confirm that the observed brightness evolution for the majority of discs can be reproduced by classical models. Further, we find that it is equally consistent with the size distribution of planetesimals predicted by particle concentration models - provided the objects are loosely bound `pebble piles' as these models also predict. Regardless of the assumed planetesimal formation mechanism, explaining the brightest debris discs in the samples uncovers a `disc mass problem'. To reproduce such discs by collisional simulations, a total mass of planetesimals of up to ˜1000 Earth masses is required, which exceeds the total mass of solids available in the protoplanetary progenitors of debris discs. This may indicate that stirring was delayed in some of the bright discs, that giant impacts occurred recently in some of them, that some systems may be younger than previously thought or that non-collisional processes contribute significantly to the dust production.

  19. Accretion flow dynamics during 1999 outburst of XTE J1859+226—modeling of broadband spectra and constraining the source mass

    Science.gov (United States)

    Nandi, Anuj; Mandal, S.; Sreehari, H.; Radhika, D.; Das, Santabrata; Chattopadhyay, I.; Iyer, N.; Agrawal, V. K.; Aktar, R.

    2018-05-01

    We examine the dynamical behavior of accretion flow around XTE J1859+226 during the 1999 outburst by analyzing the entire outburst data (˜166 days) from RXTE Satellite. Towards this, we study the hysteresis behavior in the hardness intensity diagram (HID) based on the broadband (3-150 keV) spectral modeling, spectral signature of jet ejection and the evolution of Quasi-periodic Oscillation (QPO) frequencies using the two-component advective flow model around a black hole. We compute the flow parameters, namely Keplerian accretion rate (\\dot{m}d), sub-Keplerian accretion rate (\\dot{m}h), shock location (rs) and black hole mass (M_{bh}) from the spectral modeling and study their evolution along the q-diagram. Subsequently, the kinetic jet power is computed as L^{obs}_{jet} ˜3-6 ×10^{37} erg s^{-1} during one of the observed radio flares which indicates that jet power corresponds to 8-16% mass outflow rate from the disc. This estimate of mass outflow rate is in close agreement with the change in total accretion rate (˜14%) required for spectral modeling before and during the flare. Finally, we provide a mass estimate of the source XTE J1859+226 based on the spectral modeling that lies in the range of 5.2-7.9 M_{⊙} with 90% confidence.

  20. The comparative effect of FUV, EUV and X-ray disc photoevaporation on gas giant separations

    Science.gov (United States)

    Jennings, Jeff; Ercolano, Barbara; Rosotti, Giovanni P.

    2018-04-01

    Gas giants' early (≲ 5 Myr) orbital evolution occurs in a disc losing mass in part to photoevaporation driven by high energy irradiance from the host star. This process may ultimately overcome viscous accretion to disperse the disc and halt migrating giants by starving their orbits of gas, imprinting on giant planet separations in evolved systems. Inversion of this distribution could then give insight into whether stellar FUV, EUV or X-ray flux dominates photoevaporation, constraining planet formation and disc evolution models. We use a 1D hydrodynamic code in population syntheses for gas giants undergoing Type II migration in a viscously evolving disc subject to either a primarily FUV, EUV or X-ray flux from a pre-solar T Tauri star. The photoevaporative mass loss profile's unique peak location and width in each energetic regime produces characteristic features in the distribution of giant separations: a severe dearth of ≲ 2 MJ planets interior to 5 AU in the FUV scenario, a sharp concentration of ≲ 3 MJ planets between ≈1.5 - 2 AU in the EUV case, and a relative abundance of ≈2 - 3.5 MJ giants interior to 0.5 AU in the X-ray model. These features do not resemble the observational sample of gas giants with mass constraints, though our results do show some weaker qualitative similarities. We thus assess how the differing photoevaporative profiles interact with migrating giants and address the effects of large model uncertainties as a step to better connect disc models with trends in the exoplanet population.

  1. Effects of Brass (Cu3Zn2) as High Thermal Expansion Material on Shrink Disc Performance During High Thermal Loading

    Science.gov (United States)

    Mazlan, MIS; Mohd, SA; Bahar, ND; Aziz, SAA

    2018-03-01

    This research work is focused on shrink disc operation at high temperature. Geometrical and material design selections have been done by taking into consideration the existing shrink disc operating at high temperature condition. The existing shrink disc confronted slip between shaft and shaft sleeve during thermal loading condition. The assessment has been obtained through virtual experiment by using Finite Element Analysis (FEA) -Thermal Transient Stress for 900 seconds with 300 °C of thermal loading. This investigation consists of the current and improved version of shrink disc, where identical geometries and material properties were utilized. High Thermal Expansion (HTE) material has been introduced to overcome the current design of the shrink disc. Brass (Cu3Zn2) has been selected as the HTE material in the improved shrink disc design due to its high thermal expansion properties. The HTE has shown a significant improvement on the total contact area and contact pressure on the shaft and the shaft sleeve. The improved shrink disc embedded with HTE during thermal loading exhibit a minimum of 1244.1 mm2 of the total area on shaft and shaft sleeve which uninfluenced the total contact area at normal condition which is 1254.3 mm2. Meanwhile, the total pressure of improved shrink disc had an increment of 108.1 MPa while existing shrink disc total pressure has lost 17.2 MPa during thermal loading.

  2. Do Turkish patients with lumbar disc herniation know body mechanics?

    Science.gov (United States)

    Topcu, Sacide Yildizeli

    2017-01-01

    Most common and important cause of the low back pain is lumbar disc herniation. Patients with lumbar disc herniation face with difficulties during daily activities due to the reduction of physical functions. In order to maintain daily activities without pain and discomfort, the patients should be informed about proper positions and body mechanics. The aim of the study was to determine the knowledge and the applications of the patients with lumbar disc herniation about body mechanics. This descriptive study was conducted with 75 patients with lumbar disc herniation in Edirne, Turkey. The population consisted of 75 patients who accepted to participate in the study. In the collection of data the questionnaire, which was developed according to literature by the researcher, was used. Descriptive statistics, student t-test, variance and correlation analysis were used for assessment of the data. The significance level was accepted at 0.05. It was found that 53.3% of the patients experienced awful/very severe pain. and there were some points that the patients have enough information about; mobilisation, standing, carrying the goods, leaning back while sitting, leaning somewhere while standing, getting support from the chair when standing up, avoiding sudden position changes, changing feet frequently while standing. It was detected that a statistical relation between educational level and knowledge about body mechanics exists. This study shows that individuals with lumbar disc herniation have not enough information about body mechanics and they experienced long-term severe pain. Nurses and other health care workers have important role in explaining the importance of body mechanics to the patients and should encourage them to use that in daily life.

  3. Quantitative measurement of intervertebral disc signal using MRI

    Energy Technology Data Exchange (ETDEWEB)

    Niemelaeinen, R. [Faculty of Rehabilitation Medicine, University of Alberta, Edmonton (Canada)], E-mail: riikka.niemelainen@ualberta.ca; Videman, T. [Faculty of Rehabilitation Medicine, University of Alberta, Edmonton (Canada); Dhillon, S.S. [Department of Radiology and Diagnostic Imaging, University of Alberta, Edmonton (Canada); Battie, M.C. [Faculty of Rehabilitation Medicine, University of Alberta, Edmonton (Canada)

    2008-03-15

    Aim: To investigate the spinal cord as an alternative intra-body reference to cerebrospinal fluid (CSF) in evaluating thoracic disc signal intensity. Materials and methods: T2-weighted magnetic resonance imaging (MRI) images of T6-T12 were obtained using 1.5 T machines for a population-based sample of 523 men aged 35-70 years. Quantitative data on the signal intensities were acquired using an image analysis program (SpEx (copy right) ). A random sample of 30 subjects and intraclass correlation coeffcients (ICC) were used to examine the repeatability of the spinal cord measurements. The validity of using the spinal cord as a reference was examined by correlating cord and CSF samples. Finally, thoracic disc signal was validated by correlating it with age without adjustment and adjusting for either cord or CSF. Pearson's r was used for correlational analyses. Results: The repeatability of the spinal cord signal measurements was extremely high ({>=}0.99). The correlations between the signals of spinal cord and CSF by level were all above 0.9. The spinal cord-adjusted disc signal and age correlated similarly with CSF-adjusted disc signal and age (r = -0.30 to -0.40 versus r = -0.26 to -0.36). Conclusion: Adjacent spinal cord is a good alternative reference to the current reference standard, CSF, for quantitative measurements of disc signal intensity. Clearly fewer levels were excluded when using spinal cord as compared to CSF due to missing reference samples.

  4. Squeal analysis of ventilated disc brake using ansys

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Naser, Ahmed; Allam, Essam; Abouel-seoud, Shawki [Automotive and Tractors Engineering Department., Faculty of Engineering, Helwan University, Cairo (Egypt); Ahmed, Ibrahim; Allam, Sabry [Automotive and Tractors Technology Department, Faculty of Industrial Education, Helwan University, Cairo (Egypt)

    2012-07-01

    It is well-known that automobile brakes can generate several kinds of noises. Among them is squeal, a noise in the 1-15 kHz range. It is commonly accepted that brake squeal is initiated by instability due to the friction forces, leading to self excited vibrations. To predict the onset of brake instability, a modal analysis of the prestressed structure can be performed on an improved dynamic finite element model of ventilated disc brake with friction coupling. An unsymmetric stiffness matrix is a result of the friction coupling between the brake pad and disc; this may lead to complex eigenfrequencies. The complex eigenvalue method (Unsymmetric solver) used to analyse mode shapes associated with the predicted natural frequency. Creating the element of Matrix27 between the ventilated disc and pad was very important in studying the squeal of the coupled ventilated disc brake. The results demonstrated that the FEM for the coupled ventilated rotor and pad showed a good interaction between the non-linear contact and the linear modal analysis. Furthermore, the unsymmetric solver showed that the modes of the coupled disc-pad contained two types of mode. The first type was normal mode, which did not contain an imaginary part while the second type was complex mode that contained real and imaginary parts. Moreover, complex eigenvalue analysis predicted always more unstable modes than the number of squeal frequencies that really occur in the brake system. The maximum squeal index was observed at mode 16 and at frequency of 4083 Hz with instability of 480 sec-1. However; the tendency of instability (TOI) for the system at contact stiffness of 1 GN/m was 59 that gave the lowest instability of the system.

  5. Total Disc Replacement in Lumbar Degenerative Disc Diseases.

    Science.gov (United States)

    Park, Chun Kun

    2015-11-01

    More than 10 years have passed since lumbar total disc replacement (LTDR) was introduced for the first time to the world market for the surgical management of lumbar degenerative disc disease (DDD). It seems like the right time to sum up the relevant results in order to understand where LTDR stands on now, and is heading forward to. The pathogenesis of DDD has been currently settled, but diagnosis and managements are still controversial. Fusion is recognized as golden standard of surgical managements but has various kinds of shortcomings. Lately, LTDR has been expected to replace fusion surgery. A great deal of LTDR reports has come out. Among them, more than 5-year follow-up prospective randomized controlled studies including USA IDE trials were expected to elucidate whether for LTDR to have therapeutic benefit compared to fusion. The results of these studies revealed that LTDR was not inferior to fusion. Most of clinical studies dealing with LTDR revealed that there was no strong evidence for preventive effect of LTDR against symptomatic degenerative changes of adjacent segment disease. LTDR does not have shortcomings associated with fusion. However, it has a potentiality of the new complications to occur, which surgeons have never experienced in fusion surgeries. Consequently, longer follow-up should be necessary as yet to confirm the maintenance of improved surgical outcome and to observe any very late complications. LTDR still may get a chance to establish itself as a substitute of fusion both nominally and virtually if it eases the concerns listed above.

  6. Total Disc Arthroplasty for Treating Lumbar Degenerative Disc Disease

    Science.gov (United States)

    2015-01-01

    Study Design Lumber disc arthroplasty is a technological advancement that has occurred in the last decade to treat lumbar degenerative disk diseases. Purpose The aim of this retrospective study was to establish the impact and outcomes of managing patients with lumbar degenerative disk disease who have been treated with lumbar total disc arthroplasty (TDA). Overview of Literature Several studies have shown promising results following this surgery. Methods We reviewed the files of 104 patients at the Department of Neurosurgery in Colmar (France) who had been operated on by lumbar spine arthroplasty (Prodisc) between April 2002 and October 2008. Results Among the 104 patients, 67 were female and 37 were male with an average age of 33.1 years. We followed the cases for a mean of 20 months. The most frequent level of discopathy was L4-L5 with 62 patients (59.6%) followed by L5-S1 level with 52 patients (50%). Eighty-three patients suffered from low back pain, 21 of which were associated with radiculopathy. The status of 82 patients improved after surgery according to the Oswestry Disability Index score, and 92 patients returned to work. Conclusions The results indicate that TDA is a good alternative treatment for lumbar spine disk disease, particularly for patients with disabling and chronic low back pain. This technique contributes to improve living conditions with correct patient selection for surgery. PMID:25705336

  7. Thin accretion disks in stationary axisymmetric wormhole spacetimes

    International Nuclear Information System (INIS)

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

    2009-01-01

    In this paper, we study the physical properties and the equilibrium thermal radiation emission characteristics of matter forming thin accretion disks in stationary axially symmetric wormhole spacetimes. The thin disk models are constructed by taking different values of the wormhole's angular velocity, and the time averaged energy flux, the disk temperature, and the emission spectra of the accretion disks are obtained. Comparing the mass accretion in a rotating wormhole geometry with the one of a Kerr black hole, we verify that the intensity of the flux emerging from the disk surface is greater for wormholes than for rotating black holes with the same geometrical mass and accretion rate. We also present the conversion efficiency of the accreting mass into radiation, and show that the rotating wormholes provide a much more efficient engine for the transformation of the accreting mass into radiation than the Kerr black holes. Therefore specific signatures appear in the electromagnetic spectrum of thin disks around rotating wormholes, thus leading to the possibility of distinguishing wormhole geometries by using astrophysical observations of the emission spectra from accretion disks.

  8. Regimes of mini black hole abandoned to accretion

    Science.gov (United States)

    Paik, Biplab

    2018-01-01

    Being inspired by the Eddington’s idea, along with other auxiliary arguments, it is unveiled that there exist regimes of a black hole that would prohibit accretion of ordinary energy. In explicit words, there exists a lower bound to black hole mass below which matter accretion process does not run for black holes. Not merely the baryonic matter, but, in regimes, also the massless photons could get prohibited from rushing into a black hole. However, unlike the baryon accretion abandoned black hole regime, the mass-regime of a black hole prohibiting accretion of radiation could vary along with its ambient temperature. For example, we discuss that earlier to 10‑8 s after the big-bang, as the cosmological temperature of the Universe grew above ˜ 1014 K, the mass range of black hole designating the radiation accretion abandoned regime, had to be in varying state being connected with the instantaneous age of the evolving Universe by an “one half” power law. It happens to be a fact that a black hole holding regimes prohibiting accretion of energy is gigantic by its size in comparison to the Planck length-scale. Hence the emergence of these regimes demands mini black holes for not being viable as profound suckers of energy. Consideration of accretion abandoned regimes could be crucial for constraining or judging the evolution of primordial black holes over the age of the Universe.

  9. Tracing the Evolution of Dust Obscured Star Formation and Accretion Back to the Reionisation Epoch with SPICA

    NARCIS (Netherlands)

    Gruppioni, C.; Ciesla, L.; Hatziminaoglou, E.; Pozzi, F.; Rodighiero, G.; Santini, P.; Armus, L.; Baes, M.; Braine, J.; Charmandaris, V.; Clements, D. L.; Christopher, N.; Dannerbauer, H.; Efstathiou, A.; Egami, E.; Fernández-Ontiveros, J. A.; Fontanot, F.; Franceschini, A.; González-Alfonso, E.; Griffin, M.; Kaneda, H.; Marchetti, L.; Monaco, P.; Nakagawa, T.; Onaka, T.; Papadopoulos, A.; Pearson, C.; Pérez-Fournon, I.; Peréz-González, P.; Roelfsema, P.; Scott, D.; Serjeant, S.; Spinoglio, L.; Vaccari, M.; van der Tak, F.; Vignali, C.; Wang, L.; Wada, T.

    2017-01-01

    Our current knowledge of star formation and accretion luminosity at high redshift (z > 3-4), as well as the possible connections between them, relies mostly on observations in the rest-frame ultraviolet, which are strongly affected by dust obscuration. Due to the lack of sensitivity of past and

  10. Super-Eddington accretion on to the neutron star NGC 7793 P13: Broad-band X-ray spectroscopy and ultraluminous X-ray sources

    Science.gov (United States)

    Walton, D. J.; Fürst, F.; Harrison, F. A.; Stern, D.; Bachetti, M.; Barret, D.; Brightman, M.; Fabian, A. C.; Middleton, M. J.; Ptak, A.; Tao, L.

    2018-02-01

    We present a detailed, broad-band X-ray spectral analysis of the ultraluminous X-ray source (ULX) pulsar NGC 7793 P13, a known super-Eddington source, utilizing data from the XMM-Newton, NuSTAR and Chandra observatories. The broad-band XMM-Newton+NuSTAR spectrum of P13 is qualitatively similar to the rest of the ULX sample with broad-band coverage, suggesting that additional ULXs in the known population may host neutron star accretors. Through time-averaged, phase-resolved and multi-epoch studies, we find that two non-pulsed thermal blackbody components with temperatures ∼0.5 and 1.5 keV are required to fit the data below 10 keV, in addition to a third continuum component which extends to higher energies and is associated with the pulsed emission from the accretion column. The characteristic radii of the thermal components appear to be comparable, and are too large to be associated with the neutron star itself, so the need for two components likely indicates the accretion flow outside the magnetosphere is complex. We suggest a scenario in which the thick inner disc expected for super-Eddington accretion begins to form, but is terminated by the neutron star's magnetic field soon after its onset, implying a limit of B ≲ 6 × 1012 G for the dipolar component of the central neutron star's magnetic field. Evidence of similar termination of the disc in other sources may offer a further means of identifying additional neutron star ULXs. Finally, we examine the spectrum exhibited by P13 during one of its unusual 'off' states. These data require both a hard power-law component, suggesting residual accretion on to the neutron star, and emission from a thermal plasma, which we argue is likely associated with the P13 system.

  11. Use NASA GES DISC Data in ArcGIS

    Science.gov (United States)

    Yang, Wenli; Pham, Long B.; Kempler, Steve

    2015-01-01

    This presentation describes GIS relevant data at NASA Goddard Earth Sciences Data and Information Services Center (GES DISC), GES DISC Services and Support for GIS Users, and use cases of GES DISC data in ArcGIS.

  12. MEASURING TINY MASS ACCRETION RATES ONTO YOUNG BROWN DWARFS

    International Nuclear Information System (INIS)

    Herczeg, Gregory J.; Cruz, Kelle L.; Hillenbrand, Lynne A.

    2009-01-01

    We present low-resolution Keck I/LRIS spectra spanning from 3200 to 9000 A of nine young brown dwarfs and three low-mass stars in the TW Hya Association and in Upper Sco. The optical spectral types of the brown dwarfs range from M5.5 to M8.75, though two have near-IR spectral types of early L dwarfs. We report new accretion rates derived from excess Balmer continuum emission for the low-mass stars TW Hya and Hen 3-600A and the brown dwarfs 2MASS J12073347-3932540, UScoCTIO 128, SSSPM J1102-3431, USco J160606.29-233513.3, DENIS-P J160603.9-205644, and Oph J162225-240515B, and upper limits on accretion for the low-mass star Hen 3-600B and the brown dwarfs UScoCTIO 112, Oph J162225-240515A, and USco J160723.82-221102.0. For the six brown dwarfs in our sample that are faintest at short wavelengths, the accretion luminosity or upper limit is measurable only when the image is binned over large wavelength intervals. This method extends our sensitivity to accretion rate down to ∼10 -13 M sun yr -1 for brown dwarfs. Since the ability to measure an accretion rate from excess Balmer continuum emission depends on the contrast between excess continuum emission and the underlying photosphere, for objects with earlier spectral types the upper limit on accretion rate is much higher. Absolute uncertainties in our accretion rate measurements of ∼3-5 include uncertainty in accretion models, brown dwarf masses, and distance. The accretion rate of 2 x 10 -12 M sun yr -1 onto 2MASS J12073347-3932540 is within 15% of two previous measurements, despite large changes in the Hα flux.

  13. Evaluation of Nonmydriatic Hand-held Optic Disc Photography Grading in the Philadelphia Glaucoma Detection and Treatment Project.

    Science.gov (United States)

    Waisbourd, Michael; Bond, Emily A; Sullivan, Timothy; Hu, Wanda D; Shah, Sonya B; Molineaux, Jeanne; Sembhi, Harjeet; Spaeth, George L; Myers, Jonathan S; Hark, Lisa A; Katz, L Jay

    2016-05-01

    To determine the reproducibility of optic disc photograph grading obtained by a hand-held fundus camera and to determine the diagnostic value of these photographs in detecting patients with glaucoma in a community-based glaucoma-detection program. Patients underwent slit-lamp examination by an ophthalmologist who graded each patient's optic discs using 2 methods: cup-to-disc ratio (CDR) and disc damage likelihood scale (DDLS). After a comprehensive glaucoma evaluation, patients were diagnosed as having "glaucoma," "glaucoma suspect," or "no glaucoma." Nonmydriatic, monoscopic optic disc photographs were then taken with a portable digital imaging device. On a different day, the same examiner and a second observer graded the disc photographs in a masked manner and determined a diagnostic impression based only on the disc photographs. Of the 1649 patients examined, 119 subjects were randomly selected according to 3 groups of diagnoses: "glaucoma" (n=36), "glaucoma suspect" (n=50), and "no glaucoma" (n=33). For CDR, the intraobserver agreement was 0.71 and the interobserver agreement was 0.69. For disc DDLS, the intraobserver agreement was 0.65 and the interobserver agreement was 0.67. The area under the receiver-operating characteristic distinguishing between normal and glaucoma was 0.88 and 0.86 for CDR and disc DDLS, respectively. Nonmydriatic, monoscopic disc photographs obtained by a hand-held camera had only moderate disc grading reproducibility. This could be due to a reduced quality of images, making interpretation more challenging, due to taking photographs through small pupils by a hand-held camera and the high percentage of patients with significant cataracts.

  14. Do we see accreting magnetars in X-ray pulsars?

    Directory of Open Access Journals (Sweden)

    Postnov K.A.

    2014-01-01

    Full Text Available Strong magnetic field of accreting neutron stars (1014 G is hard to probe by Xray spectroscopy but can be indirectly inferred from spin-up/spin-down measurement in X-ray pulsars. The existing observations of slowly rotating X-ray pulsars are discussed. It is shown that magnetic fields of neutron stars derived from these observations (or lower limits in some cases fall within the standard 1012-1013 G range. Claims about the evidence for accreting magnetars are critically discussed in the light of recent progress in understanding of accretion onto slowly rotating neutron stars in the subsonic regime.

  15. Sedimentation, accretion, and subsidence in marshes of Barataria Basin, Louisiana

    International Nuclear Information System (INIS)

    Hatton, R.S.; DeLaune, R.D.; Patrick, W.H. Jr.

    1983-01-01

    Vertical accretion and sediment accumulation rates were determined from the distribution of 137 Cs in cores collected from fresh water, intermediate, brackish, and salt marshes in the Barataria Basin, Louisiana. Vertical accretion rates vary from about 1.3 cm.yr -1 in levee areas to 0.7 in backmarshes. Mineral sediment content of the marsh soil profile decreased with distance from the coast. Except in natural levee areas, marsh accretion rates are less than subsidence measured by water level data, however this alone cannot account for observed land-loss patterns in the basin area

  16. Accreting fluids onto regular black holes via Hamiltonian approach

    Energy Technology Data Exchange (ETDEWEB)

    Jawad, Abdul [COMSATS Institute of Information Technology, Department of Mathematics, Lahore (Pakistan); Shahzad, M.U. [COMSATS Institute of Information Technology, Department of Mathematics, Lahore (Pakistan); University of Central Punjab, CAMS, UCP Business School, Lahore (Pakistan)

    2017-08-15

    We investigate the accretion of test fluids onto regular black holes such as Kehagias-Sfetsos black holes and regular black holes with Dagum distribution function. We analyze the accretion process when different test fluids are falling onto these regular black holes. The accreting fluid is being classified through the equation of state according to the features of regular black holes. The behavior of fluid flow and the existence of sonic points is being checked for these regular black holes. It is noted that the three-velocity depends on critical points and the equation of state parameter on phase space. (orig.)

  17. Degenerative disc disease of herniated intervertebral discs is associated with extracellular matrix remodeling, vimentin-positive cells and cell death.

    Science.gov (United States)

    Loreto, Carla; Musumeci, Giuseppe; Castorina, Alessandro; Loreto, Corrado; Martinez, Giuseppa

    2011-03-01

    We studied patients with degenerative disc disease (DDD) to demonstrate that i) remodeling of the extracellular matrix (ECM) in the intervertebral disc (IVD), particularly the elastic fiber system, of subjects with herniated discs is dysregulated and that ii) it is accompanied by accelerated elastin degradation due to increased expression of matrix metalloprotease-9 (MMP-9). Moreover we wanted to obtain a deeper insight into the pathogenesis of DDD through the study of ECM calcification, DNA fragmentation using TUNEL analysis, BAX, bcl-2 and vimentin immunopositive cells. We studied herniated discs from patients of three age groups (group 1=30-40 years; group 2=40-50 years; and group 3=50-65 years) to evaluate the oxytalan fiber systemMMP-9, apoptosis and vimentin immunopositive cells. The results demonstrated the presence of oxytalan fibers in the annulus fibrosus (AF) and the nucleus pulposus (NP) of herniated discs. In the AF oxytalan fibers replaced disrupted mature elastic fibers in calcified areas, while in the NP they were mostly found in nests at the periphery of chondrocytes. MMP-9 was prevalently observed in NP nests above all in group 1 and group 3 discs while group 2 exhibited a lower MMP-9 immunostaining. Activation of the apoptotic process was demonstrated by upregulated BAX expression in group 3. BAX immunopositivity was inversely mirrored by a significant decrease in bcl-2 expression. Intermediate filament protein vimentin was strongly expressed only in group 1 samples. A large number of apoptotic TUNEL+ cells was observed in group 3 specimens. The presence of oxytalan fibers may be the result of a process of incomplete elastogenesis, or a response to mechanical stress trying to functionally replace the lack of elastic fibers. MMP-9 expression seems to relate to disc damage, while chondrocyte BAX upregulation and TUNEL+ cell staining revealed apoptosis activation regardless of patient age. Vimentin immunopositivity was clearly detected in group 1

  18. Scanning the Magnetized Accretion Column of X-ray Pulsars with Cyclotron Lines

    Science.gov (United States)

    Schönherr, Gabriele; Wilms, J.; Kretschmar, P.; Pottschmidt, K.; Rothschild, R.; Kreykenbohm, I.; MAGNET Collaboration

    2010-03-01

    The strongly magnetized accretion column of X-ray pulsars is still not understood in many aspects like, e.g., its basic geometry and physical parameters. Cyclotron Resonance Scattering Features (short: cyclotron lines) are now becoming a possible tool to tap this mystery. As they form due to scattering processes of X-ray photons with magnetically quantized electrons in the accreted plasma, a better physical understanding of their formation and shape along with direct comparisons to observational data allows to backtrack the physical parameters and magnetic field structure in the line-forming region. High-resolution spectra with todays’ and future instruments now allow for an in-depth analysis of their shapes, promising exciting progress. We discuss results based on our new modelling attempts, which link theoretical Monte Carlo simulations directly to observational findings.

  19. Changes in disc herniation after CT-guided Percutaneous Laser Disc Decompression (PLDD): MR findings

    Science.gov (United States)

    Brat, Hugues G.; Bouziane, Tarik; Lambert, Jean; Divano, Luisa

    2004-09-01

    The aim of Percutaneous Laser Disc Decompression (PLDD) is to vaporize a small portion of the nucleus pulposus. Clinical efficacy of this technique is largely proven. However, time-evolution of intervertebral disc and its hernia after PLDD is not known. This study analyses changes in disc herniation and its native intervertebral disc at a mean follow-up of 7.5 months after PLDD in asymptomatic patients. Main observations at MRI are appearance of a high signal on T2WI in the hernia in 59%, shrinking of the hernia in 66% and overall stability of disc height.

  20. Another one grinds the dust: variability of the planetary debris disc at the white dwarf SDSS J104341.53+085558.2

    Science.gov (United States)

    Manser, Christopher J.; Gänsicke, Boris T.; Koester, Detlev; Marsh, Thomas R.; Southworth, John

    2016-10-01

    We report 9 yr of optical spectroscopy of the metal-polluted white dwarf SDSS J104341.53+085558.2, which presents morphological variations of the line profiles of the 8600 Å Ca II triplet emission from the gaseous component of its debris disc. Similar changes in the shape of the Ca II triplet have also been observed in two other systems that host a gaseous disc, and are likely related to the same mechanism. We report the Mg, Si, and Ca abundances of the debris detected in the photosphere of SDSS J1043+0855, place upper limits on O and Fe, and derive an accretion rate of (2.5-12) × 108 g s-1, consistent with those found in other systems with detected debris discs. The Mg/Si ratio and the upper limit on the Fe/Si ratio of the accreted material broadly agree with those found for the crust of the Earth. We also review the range of variability observed among white dwarfs with planetary debris discs.

  1. Thoracic disc herniation: Surgical treatment.

    Science.gov (United States)

    Court, C; Mansour, E; Bouthors, C

    2018-02-01

    Thoracic disc herniation is rare and mainly occurs between T8 and L1. The herniation is calcified in 40% of cases and is labeled as giant when it occupies more than 40% of the spinal canal. A surgical procedure is indicated when the patient has severe back pain, stubborn intercostal neuralgia or neurological deficits. Selection of the surgical approach is essential. Mid-line calcified hernias are approached from a transthoracic incision, while lateralized soft hernias can be approached from a posterolateral incision. The complication rate for transthoracic approaches is higher than that of posterolateral approaches; however, the former are performed in more complex herniation cases. The thoracoscopic approach is less invasive but has a lengthy learning curve. Retropleural mini-thoracotomy is a potential compromise solution. Fusion is recommended in cases of multilevel herniation, herniation in the context of Scheuermann's disease, when more than 50% bone is resected from the vertebral body, in patients with preoperative back pain or herniation at the thoracolumbar junction. Along with complications specific to the surgical approach, the surgical risks are neurological worsening, dural breach and subarachnoid-pleural fistulas. Giant calcified herniated discs are the largest contributor to myelopathy, intradural extension and postoperative complications. Some of the technical means that can be used to prevent complications are explored, along with how to address these complications. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  2. Optic Disc Drusen in Children

    DEFF Research Database (Denmark)

    Malmqvist, Lasse; Li, Xiao Qiang; Eckmann, Christina L

    2017-01-01

    diameter and fetal birth and pubertal parameters are associated with the presence of ODD. METHODS: This observational, longitudinal population-based birth cohort study, with a nested case-control, included 1,406 children. Eye examinations were performed when the children were between 11 and 12 years of age....... Assessment was performed of optical coherence tomography (OCT) scans from 1,304 children with gradable enhanced depth imaging scans of the optic disc. RESULTS: ODD in one or both eyes were found in 13 (1.0%) of all children. All but one of the cases were found in children with scleral canal diameter...... in the lowest quartile (1,182-1,399 μm) in the nested case-control study. Children with ODD had a mean disc diameter of 1,339 μm (interquartile range, 30 μm), whereas it was 1,508 μm (interquartile range, 196 μm) in the 130 controls without ODD (P

  3. WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Perets, Hagai B. [Technion-Israel Institute of Technology, Haifa (Israel); Kenyon, Scott J., E-mail: hperets@physics.technion.ac.il [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2013-02-20

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

  4. WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

    International Nuclear Information System (INIS)

    Perets, Hagai B.; Kenyon, Scott J.

    2013-01-01

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

  5. Cervical disc hernia operations through posterior laminoforaminotomy

    OpenAIRE

    Yolas, Coskun; Ozdemir, Nuriye Guzin; Okay, Hilmi Onder; Kanat, Ayhan; Senol, Mehmet; Atci, Ibrahim Burak; Yilmaz, Hakan; Coban, Mustafa Kemal; Yuksel, Mehmet Onur; Kahraman, Umit

    2016-01-01

    Objective: The most common used technique for posterolateral cervical disc herniations is anterior approach. However, posterior cervical laminotoforaminomy can provide excellent results in appropriately selected patients with foraminal stenosis in either soft disc prolapse or cervical spondylosis. The purpose of this study was to present the clinical outcomes following posterior laminoforaminotomy in patients with radiculopathy. Materials and Methods: We retrospectively evaluated 35 patients ...

  6. Computing Decoupled Residuals for Compact Disc Players

    DEFF Research Database (Denmark)

    Odgaard, Peter Fogh; Stoustrup, Jakob; Andersen, Palle

    2006-01-01

    In order to improve Compact Disc Players playability regarding playing Compact Discs with surface faults, like scratches and fingerprints etc, the attention has been put on fault tolerant control schemes. Almost every of those methods are based on fault detection. The standard approach is to use...

  7. Magnetorotational instability and dynamo action in gravito-turbulent astrophysical discs

    Science.gov (United States)

    Riols, A.; Latter, H.

    2018-02-01

    Though usually treated in isolation, the magnetorotational and gravitational instabilities (MRI and GI) may coincide at certain radii and evolutionary stages of protoplanetary discs and active galactic nuclei. Their mutual interactions could profoundly influence several important processes, such as accretion variability and outbursts, fragmentation and disc truncation, or large-scale magnetic field production. Direct numerical simulations of both instabilities are computationally challenging and remain relatively unexplored. In this paper, we aim to redress this neglect via a set of 3D vertically stratified shearing-box simulations, combining self-gravity and magnetic fields. We show that gravito-turbulence greatly weakens the zero-net-flux MRI. In the limit of efficient cooling (and thus enhanced GI), the MRI is completely suppressed, and yet strong magnetic fields are sustained by the gravito-turbulence. This turbulent `spiral wave' dynamo may have widespread application, especially in galactic discs. Finally, we present preliminary work showing that a strong net-vertical-flux revives the MRI and supports a magnetically dominated state in which the GI is secondary.

  8. Accretion from a clumpy massive-star wind in supergiant X-ray binaries

    Science.gov (United States)

    El Mellah, I.; Sundqvist, J. O.; Keppens, R.

    2018-04-01

    Supergiant X-ray binaries (SgXB) host a compact object, often a neutron star (NS), orbiting an evolved O/B star. Mass transfer proceeds through the intense line-driven wind of the stellar donor, a fraction of which is captured by the gravitational field of the NS. The subsequent accretion process on to the NS is responsible for the abundant X-ray emission from SgXB. They also display peak-to-peak variability of the X-ray flux by a factor of a few 10-100, along with changes in the hardness ratios possibly due to varying absorption along the line of sight. We use recent radiation-hydrodynamic simulations of inhomogeneities (a.k.a. clumps) in the non-stationary wind of massive hot stars to evaluate their impact on the time-variable accretion process. For this, we run 3D hydrodynamic simulations of the wind in the vicinity of the accretor to investigate the formation of the bow shock and follow the inhomogeneous flow over several spatial orders of magnitude, down to the NS magnetosphere. In particular, we show that the impact of the wind clumps on the time variability of the intrinsic mass accretion rate is severely tempered by the crossing of the shock, compared to the purely ballistic Bondi-Hoyle-Lyttleton estimation. We also account for the variable absorption due to clumps passing by the line of sight and estimate the final effective variability of the column density and mass accretion rate for different orbital separations. Finally, we compare our results to the most recent analysis of the X-ray flux and the hardness ratio in Vela X-1.

  9. Regression of a symptomatic thoracic disc herniation with a calcified intervertebral disc component

    Directory of Open Access Journals (Sweden)

    Hidayet Sari

    2016-12-01

    Full Text Available There were only a few cases describing spontaneous regression of calcified thoracic disc herniation in the literature. We present a 38-year-old male office worker who had left paramedian-foraminal extruded disc at T7–T8 with calcifications of the T7–T8 and T8–T9 intervertebral discs. This case was unique in that the non-calcified extruded disc material regressed almost completely in 5 months while the calcified intervertebral discs remained the same during the process of regression. This report stresses that regression of the herniated material of the thoracic discs with subsidence of the symptoms is still possible even if the disc material is calcified.

  10. Accreting Binary Populations in the Earlier Universe

    Science.gov (United States)

    Hornschemeier, Ann

    2010-01-01

    It is now understood that X-ray binaries dominate the hard X-ray emission from normal star-forming galaxies. Thanks to the deepest (2-4 Ms) Chandra surveys, such galaxies are now being studied in X-rays out to z approximates 4. Interesting X-ray stacking results (based on 30+ galaxies per redshift bin) suggest that the mean rest-frame 2-10 keV luminosity from z=3-4 Lyman break galaxies (LBGs), is comparable to the most powerful starburst galaxies in the local Universe. This result possibly indicates a similar production mechanism for accreting binaries over large cosmological timescales. To understand and constrain better the production of X-ray binaries in high-redshift LBGs, we have utilized XMM-Newton observations of a small sample of z approximates 0.1 GALEX-selected Ultraviolet-Luminous Galaxies (UVLGs); local analogs to high-redshift LBGs. Our observations enable us to study the X-ray emission from LBG-like galaxies on an individual basis, thus allowing us to constrain object-to-object variances in this population. We supplement these results with X-ray stacking constraints using the new 3.2 Ms Chandra Deep Field-South (completed spring 2010) and LBG candidates selected from HST, Swift UVOT, and ground-based data. These measurements provide new X-ray constraints that sample well the entire z=0-4 baseline

  11. Black Hole Accretion in Gamma Ray Bursts

    Directory of Open Access Journals (Sweden)

    Agnieszka Janiuk

    2017-02-01

    Full Text Available We study the structure and evolution of the hyperaccreting disks and outflows in the gamma ray bursts central engines. The torus around a stellar mass black hole is composed of free nucleons, Helium, electron-positron pairs, and is cooled by neutrino emission. Accretion of matter powers the relativistic jets, responsible for the gamma ray prompt emission. The significant number density of neutrons in the disk and outflowing material will cause subsequent formation of heavier nuclei. We study the process of nucleosynthesis and its possible observational consequences. We also apply our scenario to the recent observation of the gravitational wave signal, detected on 14 September 2015 by the two Advanced LIGO detectors, and related to an inspiral and merger of a binary black hole system. A gamma ray burst that could possibly be related with the GW150914 event was observed by the Fermi satellite. It had a duration of about 1 s and appeared about 0.4 s after the gravitational-wave signal. We propose that a collapsing massive star and a black hole in a close binary could lead to the event. The gamma ray burst was powered by a weak neutrino flux produced in the star remnant’s matter. Low spin and kick velocity of the merged black hole are reproduced in our simulations. Coincident gravitational-wave emission originates from the merger of the collapsed core and the companion black hole.

  12. Feature-based handling of surface faults in compact disc players

    DEFF Research Database (Denmark)

    Odgaard, Peter Fogh; Stoustrup, Jakob; Andersen, Palle

    2006-01-01

    In this paper a novel method called feature-based control is presented. The method is designed to improve compact disc players’ handling of surface faults on the discs. The method is based on a fault-tolerant control scheme, which uses extracted features of the surface faults to remove those from...... the detector signals used for control during the occurrence of surface faults. The extracted features are coefficients of Karhunen–Loève approximations of the surface faults. The performance of the feature-based control scheme controlling compact disc players playing discs with surface faults has been...... validated experimentally. The proposed scheme reduces the control errors due to the surface faults, and in some cases where the standard fault handling scheme fails, our scheme keeps the CD-player playing....

  13. Comparison between cranial thoracic intervertebral disc herniations in German Shepherd dogs and other large breed dogs.

    Science.gov (United States)

    Gaitero, Luis; Nykamp, Stephanie; Daniel, Rob; Monteith, Gabrielle

    2013-01-01

    Cranial thoracic intervertebral disc herniations have been reported to be rare in dogs due to the presence of the intercapital ligament, however some studies have proposed they may not be uncommon in German Shepherd dogs. The purpose of this retrospective study was to compare cranial thoracic intervertebral disc herniations in German Shepherd dogs and other large breed dogs (control group). Medical records at the Ontario Veterinary College were searched for German Shepherd dogs and other large breed dogs that had magnetic resonance imaging studies including the T1-T9 region. For each dog and each disc space from T1-T9, three variables (compression, disc degeneration, and herniation) were recorded and graded based on review of sagittal T2-weighted images. Twenty-three German Shepherd dogs and 47 other large breed dogs met inclusion criteria. The German Shepherd dog group had higher scores than the control group for compression (P = 0.0099) and herniation (P Shepherd dog group, intervertebral discs T2-T3 and T4-T5 had an increased risk for compression and T3-T4 had an increased risk for compression and herniation. Findings from this study indicated that German Shepherd dogs may be more likely than other large breed dogs to have spinal cord compression due to cranial thoracic disc herniations. Imaging of the cranial thoracic spine, including T2-T3, is recommended for German Shepherd dogs with T3-L3 neurological signs. © 2012 Veterinary Radiology & Ultrasound.

  14. Lumbar disc cyst with contralateral radiculopathy

    Directory of Open Access Journals (Sweden)

    Kishore Tourani

    2012-08-01

    Full Text Available Disc cysts are uncommon intraspinal cystic lesions located in the ventrolateral epidural space. They communicate with the nucleus pulposus of the intervertebral disc and cause symptoms by radicular compression. We report a unique case of lumbar disc cyst that was associated with disc herniation and contralateral radiculopathy. A 22 year old male presented with one month history of back-ache radiating to the left leg. Magnetic Resonance Imaging (MRI showed L3-L4 disc herniation with annular tear and cystic lesion in the extradural space anterior to the thecal sac on right side, which increased in size over a period of 3 weeks. L3 laminectomy and bilateral discectomy and cyst excision was done with partial improvement of patients symptoms.

  15. Spontaneous Regression of Lumbar Herniated Disc

    Directory of Open Access Journals (Sweden)

    Chun-Wei Chang

    2009-12-01

    Full Text Available Intervertebral disc herniation of the lumbar spine is a common disease presenting with low back pain and involving nerve root radiculopathy. Some neurological symptoms in the majority of patients frequently improve after a period of conservative treatment. This has been regarded as the result of a decrease of pressure exerted from the herniated disc on neighboring neurostructures and a gradual regression of inflammation. Recently, with advances in magnetic resonance imaging, many reports have demonstrated that the herniated disc has the potential for spontaneous regression. Regression coincided with the improvement of associated symptoms. However, the exact regression mechanism remains unclear. Here, we present 2 cases of lumbar intervertebral disc herniation with spontaneous regression. We review the literature and discuss the possible mechanisms, the precipitating factors of spontaneous disc regression and the proper timing of surgical intervention.

  16. Magnetic resonance imaging of intervertebral disc degeneration

    International Nuclear Information System (INIS)

    Maeda, Hiroshi; Noguchi, Masao; Kira, Hideaki; Fujiki, Hiroshi; Shimokawa, Isao; Hinoue, Kaichi.

    1993-01-01

    The aim of this study was to correlate the degree of lumbar intervertebral disc degeneration with findings of magnetic resonance imaging (MRI). Seventeen autopsied (from 7 patients) and 21 surgical (from 20 patients) intervertebral discs were used as specimens for histopathological examination. In addition, 21 intervertebral discs were examined on T2-weighted images. Histopathological findings from both autopsied and surgical specimens were well correlated with MRI findings. In particular, T2-weighted images reflected increased collagen fibers and rupture within the fibrous ring accurately. However, when severely degenerated intervertebral discs and hernia protruding the posterior longitudinal ligament existed, histological findings were not concordant well with T2-weighted images. Morphological appearances of autopsy specimens, divided into four on T2-weighted images, were well consistent with histological degeneration. This morphological classification, as shown on T2-weighted images, could also be used in the evaluation of intervertebral disc degeneration. (N.K.)

  17. Magnetic resonance imaging of intervertebral disc degeneration

    Energy Technology Data Exchange (ETDEWEB)

    Maeda, Hiroshi; Noguchi, Masao (Kitakyushu City Yahata Hospital, Fukuoka (Japan)); Kira, Hideaki; Fujiki, Hiroshi; Shimokawa, Isao; Hinoue, Kaichi

    1993-02-01

    The aim of this study was to correlate the degree of lumbar intervertebral disc degeneration with findings of magnetic resonance imaging (MRI). Seventeen autopsied (from 7 patients) and 21 surgical (from 20 patients) intervertebral discs were used as specimens for histopathological examination. In addition, 21 intervertebral discs were examined on T2-weighted images. Histopathological findings from both autopsied and surgical specimens were well correlated with MRI findings. In particular, T2-weighted images reflected increased collagen fibers and rupture within the fibrous ring accurately. However, when severely degenerated intervertebral discs and hernia protruding the posterior longitudinal ligament existed, histological findings were not concordant well with T2-weighted images. Morphological appearances of autopsy specimens, divided into four on T2-weighted images, were well consistent with histological degeneration. This morphological classification, as shown on T2-weighted images, could also be used in the evaluation of intervertebral disc degeneration. (N.K.).

  18. Protoplanetary disc response to distant tidal encounters in stellar clusters

    Science.gov (United States)

    Winter, A. J.; Clarke, C. J.; Rosotti, G.; Booth, R. A.

    2018-04-01

    The majority of stars form in a clustered environment. This has an impact on the evolution of surrounding protoplanetary discs (PPDs) due to either photoevaporation or tidal truncation. Consequently, the development of planets depends on formation environment. Here, we present the first thorough investigation of tidally induced angular momentum loss in PPDs in the distant regime, partly motivated by claims in the literature for the importance of distant encounters in disc evolution. We employ both theoretical predictions and dynamical/hydrodynamical simulations in 2D and 3D. Our theoretical analysis is based on that of Ostriker (1994) and leads us to conclude that in the limit that the closest approach distance xmin ≫ r, the radius of a particle ring, the fractional change in angular momentum scales as (xmin/r)-5. This asymptotic limit ensures that the cumulative effect of distant encounters is minor in terms of its influence on disc evolution. The angular momentum transfer is dominated by the m = 2 Lindblad resonance for closer encounters and by the m = 1, ω = 0 Lindblad resonance at large xmin/r. We contextualize these results by comparing expected angular momentum loss for the outer edge of a PPD due to distant and close encounters. Contrary to the suggestions of previous works, we do not find that distant encounters contribute significantly to angular momentum loss in PPDs. We define an upper limit for closest approach distance where interactions are significant as a function of arbitrary host to perturber mass ratio M2/M1.

  19. Solar neighbourhood and Galactic disc(s: New constraints

    Directory of Open Access Journals (Sweden)

    Schönrich R.

    2012-02-01

    Full Text Available We present a re-analysis of the Geneva-Copenhagen survey, based on improved effective temperature and metallicity scales, which also provide a better match to theoretical isochrones. The latter are used for a Bayesian investigation on stellar ages. With respect to previous analyses, our stars are on average 100 K hotter and 0.1 dex more metal rich, which shifts the peak of the metallicity distribution function around the solar value. From Strömgren photometry we are able to derive for the first time a proxy for alpha elements, which enables us to perform a tentative dissection of the chemical thin and thick disc. We find evidence for the latter being composed of an old, mildly but systematically alpha-enhanced population that extends to super solar metallicities, in agreement with spectroscopic studies. Our analysis suggests a strong interplay among ages, abundances and kinematics of stars.

  20. Open Source GIS Connectors to NASA GES DISC Satellite Data

    Science.gov (United States)

    Kempler, Steve; Pham, Long; Yang, Wenli

    2014-01-01

    The NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) houses a suite of high spatiotemporal resolution GIS data including satellite-derived and modeled precipitation, air quality, and land surface parameter data. The data are valuable to various GIS research and applications at regional, continental, and global scales. On the other hand, many GIS users, especially those from the ArcGIS community, have difficulties in obtaining, importing, and using our data due to factors such as the variety of data products, the complexity of satellite remote sensing data, and the data encoding formats. We introduce a simple open source ArcGIS data connector that significantly simplifies the access and use of GES DISC data in ArcGIS.

  1. Surgical management for lumbar disc herniation in pregnancy.

    Science.gov (United States)

    Kapetanakis, S; Giovannopoulou, E; Blontzos, N; Kazakos, G; Givissis, P

    2017-12-01

    Lumbar disc herniation is a common surgical spine pathology that may be presented during pregnancy. The state of pregnancy complicates the diagnosis and therapeutical management of this entity. Specific considerations rule the decision for surgical intervention, the optimal timing of it and the type of selected procedure in a pregnant patient, due to the potential risks for the fetus. In the last 30 years, evolution in the field of spine surgery has provided options other than open standard discectomy. The well-established concept of "minimal intervention" has led to the development of microdiscectomy and other innovative, full-endoscopic techniques for lumbar discectomy. The aim of the present study is to review the surgical management of lumbar disc herniation in pregnancy and investigate the potential role of minimally invasive spine surgery in this specific population. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  2. Multi-time-scale X-ray reverberation mapping of accreting black holes

    Science.gov (United States)

    Mastroserio, Guglielmo; Ingram, Adam; van der Klis, Michiel

    2018-04-01

    Accreting black holes show characteristic reflection features in their X-ray spectrum, including an iron Kα line, resulting from hard X-ray continuum photons illuminating the accretion disc. The reverberation lag resulting from the path-length difference between direct and reflected emission provides a powerful tool to probe the innermost regions around both stellar-mass and supermassive black holes. Here, we present for the first time a reverberation mapping formalism that enables modelling of energy-dependent time lags and variability amplitude for a wide range of variability time-scales, taking the complete information of the cross-spectrum into account. We use a pivoting power-law model to account for the spectral variability of the continuum that dominates over the reverberation lags for longer time-scale variability. We use an analytic approximation to self-consistently account for the non-linear effects caused by this continuum spectral variability, which have been ignored by all previous reverberation studies. We find that ignoring these non-linear effects can bias measurements of the reverberation lags, particularly at low frequencies. Since our model is analytic, we are able to fit simultaneously for a wide range of Fourier frequencies without prohibitive computational expense. We also introduce a formalism of fitting to real and imaginary parts of our cross-spectrum statistic, which naturally avoids some mistakes/inaccuracies previously common in the literature. We perform proof-of-principle fits to Rossi X-ray Timing Explorer data of Cygnus X-1.

  3. Can Halogen Enrichment in Reduced Enstatite Chondrites Provide Clues to Volatile Accretion in the Early Earth?

    Science.gov (United States)

    Clay, P. L.; Burgess, R.; Busemann, H.; Ruzié, L.; Joachim, B.; Ballentine, C.

    2013-12-01

    Understanding how the Earth obtained and ultimately retained its volatiles is important for our overall understanding of large scale planetary evolution. Numerous models exist for the heterogeneous accretion of volatiles to early Earth, but accounting for all elements through accretion of typical planetary building blocks (e.g., CI chondrites) is difficult. Proto-planetary collisions resulting in the accretion of volatile-poor material under reducing conditions followed by accretion of volatile-rich material under oxidizing conditions has been suggested in such models [e.g., 1]. The heavy halogens (Cl, Br and I), a group of moderately volatile elements, are excellent tracers of planetary processing due to their low abundance and incompatible nature. Therefore characterizing halogen abundance and distribution in materials that accreted to form the planets, e.g., primitive meteorites, is crucial. One group of primitive meteorites, the enstatite chondrites (EC's), are amongst the most reduced materials in the solar system as evidenced by their unique mineral assemblage. Yet despite forming under ultra-reducing conditions, they are enriched in the moderately volatile elements, such as the halogens. The ECs are of particular interest owing to their oxygen isotopic composition which plots along the terrestrial fractionation line, linking them isotopically to the Earth-Moon system. These samples can thus potentially provide clues on the accretion of moderately volatile element rich material under reducing conditions, such as it may have existed during the early stages of Earth's accretion. Chlorine, Br and I concentrations in ECs were determined through step-heating small neutron-irradiated samples (0.3 to 3.3 mg) and measured by mass spectrometry using the noble gas proxy isotopes 38ArCl/Cl, 80KrBr/Br and 128XeI/I. The EH chondrites are consistently enriched in the heavy halogens (up to 330 ppm Cl, 2290 ppb Br and 180 ppb I), compared to other ordinary and carbonaceous

  4. Analogue Hawking radiation from astrophysical black-hole accretion

    International Nuclear Information System (INIS)

    Das, Tapas K

    2004-01-01

    We show that spherical accretion onto astrophysical black holes can be considered as a natural example of an analogue system. We provide, for the first time, an exact analytical scheme for calculating the analogue Hawking temperature and surface gravity for general relativistic accretion onto astrophysical black holes. Our calculation may bridge the gap between the theory of transonic astrophysical accretion and the theory of analogue Hawking radiation. We show that the domination of the analogue Hawking temperature over the actual Hawking temperature may be a real astrophysical phenomenon, though observational tests of this fact will at best be difficult and at worst might prove to be impossible. We also discuss the possibilities of the emergence of analogue white holes around astrophysical black holes. Our calculation is general enough to accommodate accreting black holes with any mass

  5. Angular Momentum Transport in Quasi-Keplerian Accretion Disks ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Keplerian accretion disk yield results that are inconsistent with the generally accepted model. If correct, the ideas proposed by Hayashi &. Matsuda would radically alter our understanding of the nature of the angular momentum transport in the disk, ...

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

    Science.gov (United States)

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

    2014-06-05

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

  7. Magnetospheres of accreting compact objects in binary systems

    International Nuclear Information System (INIS)

    Aly, J.J.

    1985-09-01

    Bright pulsating X-ray sources (X-ray pulsars, AM Her stars,...) have been identified as strongly magnetized compact objects accreting matter from a binary companion. We give here a summary of some of the work which has been recently done to try to understand the interaction between the magnetic field of the compact object and the matter around. We examine in turn the models describing the interaction of the field with: i) a spherically symmetric accretion flow; ii) a thin keplerian accretion disk; iii) the companion itself. In all these cases, we pay particular attention to the following problems: i) how the external plasma interacting with the magnetosphere can get mixed with the field; ii) by which mechanism the magnetic field controls the mass-momentum-energy exchanges between the two stars. In conclusion, we compare the magnetosphere of an accreting compact object with that one of a planet [fr

  8. Which iodinated contrast media is the least cytotoxic to human disc cells?

    Science.gov (United States)

    Kim, Kyung-Hyun; Park, Jeong-Yoon; Park, Hyo-Suk; Kuh, Sung-Uk; Chin, Dong-Kyu; Kim, Keun-Su; Cho, Yong-Eun

    2015-05-01

    Iodinated contrast media (CM) is commonly used for various intradiscal injections such as in discography and endoscopic spinal surgery. However, CM has been shown to be toxic to renal tissue due to its ionic strength and osmolarity and as a result of iodine-induced cytotoxicity, which has raised concern over whether there are similar negative effects on disc cells. This in vitro study was designed to identify the least cytotoxic iodinated CM to the human disc cell among four different physiochemical iodinated contrast dyes. In vitro laboratory study. Intervertebral disc tissue was obtained by discectomy from a total of 10 lumbar disc patients undergoing surgery and disc cells were isolated. The human disc cells were grown in 3D alginate bead culture with 0, 0.1, 10, and 100 mg/mL CM solutions (ionic dimer, ionic monomer, non-ionic dimer, and non-ionic monomer) and mannitol as a control for 2 days. The living cells were analyzed with trypan blue staining. Fluorescence-activated cell sorting analysis was performed using Annexin V and propidium iodide (PI) and 3D alginate bead immunostaining to identify live, apoptotic, and necrotic cells. Human disc cell death was time- and dose-dependent in response to CM and more necrosis was observed than apoptosis. In addition, non-ionic dimeric CM (iodixanol) showed the least toxic effect on human disc cells, followed by non-ionic monomeric (iopromide), ionic dimeric (ioxaglate), and ionic monomeric CM (ioxithalamate). Contrast media is cytotoxic to human disc cells in a dose- and time-dependent manner. This in vitro study revealed that, among four different CM preparations, non-ionic dimeric CM is the least detrimental to human disc cell viability. Careful attention should be paid to the type of CM chosen for discography and endoscopic spinal surgery. It is also necessary to investigate the detrimental effects of CM on disc cells and disc degeneration in further in vivo studies. Copyright © 2015 Elsevier Inc. All rights

  9. On accretion of dark energy onto black and wormholes

    OpenAIRE

    Jiménez Madrid, J. A.; Martín Moruno, Prado

    2010-01-01

    We review some of the possible models that are able to describe the current Universe which point out the future singularities that could appear. We show that the study of the dark energy accretion onto black- and worm-holes phenomena in these models could lead to unexpected consequences, allowing even the avoidance of the considered singularities. We also review the debate about the approach used to study the accretion phenomenon which has appeared in literature to demonstrate the advantages ...

  10. On Hydromagnetic Stresses in Accretion Disk Boundary Layers

    DEFF Research Database (Denmark)

    Pessah, Martin Elias; Chan, Chi-kwan

    2012-01-01

    Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear...... of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity...

  11. TW Hya: SPECTRAL VARIABILITY, X-RAYS, AND ACCRETION DIAGNOSTICS

    International Nuclear Information System (INIS)

    Dupree, A. K.; Brickhouse, N. S.; Cranmer, S. R.; Luna, G. J. M.; Schneider, E. E.; Bessell, M. S.; Bonanos, A.; Crause, L. A.; Lawson, W. A.; Mallik, S. V.; Schuler, S. C.

    2012-01-01

    The nearest accreting T Tauri star, TW Hya was intensively and continuously observed over ∼17 days with spectroscopic and photometric measurements from four continents simultaneous with a long segmented exposure using the Chandra satellite. Contemporaneous optical photometry from WASP-S indicates a 4.74 day period was present during this time. The absence of a similar periodicity in the Hα flux and the total X-ray flux which are dominated by accretion processes and the stellar corona, respectively, points to a different source of photometric variations. The Hα emission line appears intrinsically broad and symmetric, and both the profile and its variability suggest an origin in the post-shock cooling region. An accretion event, signaled by soft X-rays, is traced spectroscopically for the first time through the optical emission line profiles. After the accretion event, downflowing turbulent material observed in the Hα and Hβ lines is followed by He I (λ5876) broadening near the photosphere. Optical veiling resulting from the heated photosphere increases with a delay of ∼2 hr after the X-ray accretion event. The response of the stellar coronal emission to an increase in the veiling follows ∼2.4 hr later, giving direct evidence that the stellar corona is heated in part by accretion. Subsequently, the stellar wind becomes re-established. We suggest a model that incorporates the dynamics of this sequential series of events: an accretion shock, a cooling downflow in a supersonically turbulent region, followed by photospheric and later, coronal heating. This model naturally explains the presence of broad optical and ultraviolet lines, and affects the mass accretion rates determined from emission line profiles.

  12. Advective accretion flow properties around rotating black holes ...

    Indian Academy of Sciences (India)

    RAMIZ AKTAR

    2018-02-10

    Feb 10, 2018 ... in black hole source GRO J1655-40. While doing this, we attempt to constrain the range of ak based on observed. HFQPOs (∼300 Hz and ∼450 Hz) for the black hole source GRO J1655-40. Keywords. Accretion: accretion disc—black hole physics—shock waves—ISM: jets and outflows—X-ray: binaries. 1.

  13. Study of fatigue failure in Pelton turbine rotor discs; Estudo de falhas por fadiga em discos para rotores de turbina Pelton

    Energy Technology Data Exchange (ETDEWEB)

    D`Avila, Marcio Galdino; Tomazelli, Ana T.A.M.A.; Sertori, Sergio Reinaldo [Eletricidade de Sao Paulo SA, SP (Brazil); Kuronuma, Toshiyuki; Gioielli, Paulo Costa; Masiukewycz, Alexius [Instituto de Pesquisas Tecnologicas (IPT), Sao Paulo, SP (Brazil)

    1995-12-31

    The failures which took place in two Pelton turbine discs at Henry Borden hydroelectric power plant leaded to a study in order to determine the causes of such problems and avoid new occurrences. It was determined that such failures happened due to the disc`s assemblage criteria which were determined by the manufacturer, and caused micro-movements among the equipment parts. This work discusses the above mentioned issues 1 ref., 3 figs.

  14. A Systems-Level Perspective on Engine Ice Accretion

    Science.gov (United States)

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

    2013-01-01

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

  15. Thermal structure of accreting neutron stars and strange stars

    International Nuclear Information System (INIS)

    Miralda-Escude, J.; Paczynski, B.; Haensel, P.

    1990-01-01

    Steady-state models of accreting neutron stars and strange stars are presented, and their properties as a function of accretion rate are analyzed. The models have steady-state envelopes, with stationary hydrogen burning taken into account, the helium shell flashes artificially suppressed, and the crust with a large number of secondary heat sources. The deep interiors are almost isothermal and are close to thermal equilibrium. A large number of models were calculated for many values of the accretion rates, with ordinary, pion-condensed, and strange cores, with and without secondary heat sources in the crust, and with the heavy element content of the accreting matter in the range Z = 0.0002-0.02. All models show a similar pattern of changes as the accretion rate is varied. For low accretion rates, the hydrogen burning shell is unstable; for intermediate rates, the hydrogen burning shell is stable, but helium burning is not; for high rates, the two shell sources burn together and are unstable. 60 refs

  16. Implementation and Validation of 3-D Ice Accretion Measurement Methodology

    Science.gov (United States)

    Lee, Sam; Broeren, Andy P.; Kreeger, Richard E.; Potapczuk, Mark; Utt, Lloyd

    2014-01-01

    A research program has been implemented to develop and validate the use of a commercial 3-D laser scanning system to record ice accretion geometry in the NASA Icing Research Tunnel. A main component of the program was the geometric assessment of the 3- D laser scanning system on a 2-D (straight wing) and a 3-D (swept wing) airfoil geometries. This exercise consisted of comparison of scanned ice accretion to castings of the same ice accretion. The scan data were also used to create rapid prototype artificial ice shapes that were scanned and compared to the original ice accretion. The results from geometric comparisons on the straight wing showed that the ice shape models generated through the scan/rapid prototype process compared reasonably well with the cast shapes. Similar results were obtained with the geometric comparisons on the swept wing. It was difficult to precisely compare the scans of the cast shapes to the original ice accretion scans because the cast shapes appear to have shrunk during the mold/casting process by as much as 0.10-inch. However the comparison of the local ice-shape features were possible and produced better results. The rapid prototype manufacturing process was shown to reproduce the original ice accretion scan normally within 0.01-inch.

  17. The radiative efficiency of a radiatively inefficient accretion flow

    Science.gov (United States)

    D'Angelo, C. R.; Fridriksson, J. K.; Messenger, C.; Patruno, A.

    2015-05-01

    A recent joint XMM-Newton/Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the accreting neutron star Cen X-4 (LX ˜ 1033 erg s-1) revealed a hard power-law component (Γ ˜ 1-1.5) with a relatively low cut-off energy (˜10 keV), suggesting bremsstrahlung emission. The physical requirements for bremsstrahlung combined with other observed properties of Cen X-4 suggest the emission comes from a boundary layer rather than the accretion flow. The accretion flow itself is thus undetected (with an upper limit of Lflow ≲ 0.3LX). A deep search for coherent pulsations (which would indicate a strong magnetic field) places a 6 per cent upper limit on the fractional amplitude of pulsations, suggesting the flow is not magnetically regulated. Considering the expected energy balance between the accretion flow and the boundary layer for different values of the neutron star parameters (size, magnetic field, and spin) we use the upper limit on Lflow to set an upper limit of ε ≲ 0.3 for the intrinsic radiative efficiency of the accretion flow for the most likely model of a fast-spinning, non-magnetic neutron star. The non-detection of the accretion flow provides the first direct evidence that this flow is indeed `radiatively inefficient', i.e. most of the gravitational potential energy lost by the flow before it hits the star is not emitted as radiation.

  18. [Physiotherapy in lumbar disc herniation ].

    Science.gov (United States)

    Stoll, T; Germann, D; Hagmann, H

    2001-08-01

    Physiotherapy is the treatment of choice in patients with symptoms caused by a lumbar disc herniation. In clinical practice a broad range of physiotherapeutic modalities has been revealed to be helpful. During the acute stage the efficacy of the McKenzie-concept, mobilisation therapies and traction has been demonstrated in randomized controlled trials with a blind assessor. In addition, pain reducing physical therapies such as cold or electrotherapy and non-steroidal anti-inflammatory drugs, analgesics and/or muscle relaxants are sensible initial accompanying treatments. The effectiveness of active physiotherapies such as training of local strength endurance of back and abdominal muscles has been proven in patients during the chronic stage. The indications for a in-patient rehabilitation programme, for surgery and the danger of developing chronic low back pain are discussed.

  19. Lumbar herniated disc: spontaneous regression.

    Science.gov (United States)

    Altun, Idiris; Yüksel, Kasım Zafer

    2017-01-01

    Low back pain is a frequent condition that results in substantial disability and causes admission of patients to neurosurgery clinics. To evaluate and present the therapeutic outcomes in lumbar disc hernia (LDH) patients treated by means of a conservative approach, consisting of bed rest and medical therapy. This retrospective cohort was carried out in the neurosurgery departments of hospitals in Kahramanmaraş city and 23 patients diagnosed with LDH at the levels of L3-L4, L4-L5 or L5-S1 were enrolled. The average age was 38.4 ± 8.0 and the chief complaint was low back pain and sciatica radiating to one or both lower extremities. Conservative treatment was administered. Neurological examination findings, durations of treatment and intervals until symptomatic recovery were recorded. Laségue tests and neurosensory examination revealed that mild neurological deficits existed in 16 of our patients. Previously, 5 patients had received physiotherapy and 7 patients had been on medical treatment. The number of patients with LDH at the level of L3-L4, L4-L5, and L5-S1 were 1, 13, and 9, respectively. All patients reported that they had benefit from medical treatment and bed rest, and radiologic improvement was observed simultaneously on MRI scans. The average duration until symptomatic recovery and/or regression of LDH symptoms was 13.6 ± 5.4 months (range: 5-22). It should be kept in mind that lumbar disc hernias could regress with medical treatment and rest without surgery, and there should be an awareness that these patients could recover radiologically. This condition must be taken into account during decision making for surgical intervention in LDH patients devoid of indications for emergent surgery.

  20. Minimizing cryopreservation-induced loss of disc cell activity for storage of whole intervertebral discs

    Directory of Open Access Journals (Sweden)

    SCW Chan

    2010-06-01

    Full Text Available Severe intervertebral disc (IVD degeneration often requires disc excision and spinal fusion, which leads to loss of spinal segment mobility. Implantation of an allograft disc or tissue engineered disc construct emerges as an alternative to artificial disc replacement for preserving the motion of the degenerated level. Establishment of a bank of cadaveric or engineered cryopreserved discs enables size matching, and facilitates clinical management. However, there is a lack of understanding of the behaviour of disc cells during cryopreservation, as well as how to maximize their survival, such that disc graft properties can be preserved. Here, we report on the effect of alterations in cooling rates, cryoprotective agents (CPAs, and duration of pre-cryopreservation incubation in CPA on cellular activity in whole porcine lumbar discs. Our results indicated that cooling rates of -0.3°C/min and -0.5°C /min resulted in the least loss of metabolic activity in nucleus pulposus (NP and annulus fibrosus (AF respectively, while metabolic activity is best maintained by using a combination of 10% dimethylsulphoxide (DMSO and 10% propylene-glycol (PG as CPA. By the use of such parameters, metabolic activity of the NP and the AF cells could be maintained at 70% and 45%, respectively, of that of the fresh tissue. Mechanical testing and histological evaluation showed no significant differences in mechanical properties or alterations in disc structure compared to fresh discs. Despite the limitations of the animal model, our findings provide a framework for establishing an applicable cryopreservation protocol for human disc allografts or tissue-engineered disc constructs.