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Sample records for disc instability dependency

  1. Kozai-Lidov disc instability

    NASA Astrophysics Data System (ADS)

    Lubow, Stephen H.; Ogilvie, Gordon I.

    2017-08-01

    Recent results by Martin et al. showed in 3D smoothed particle hydrodynamics simulations that tilted discs in binary systems can be unstable to the development of global, damped Kozai-Lidov (KL) oscillations in which the discs exchange tilt for eccentricity. We investigate the linear stability of KL modes for tilted inviscid discs under the approximations that the disc eccentricity is small and the disc remains flat. By using 1D equations, we are able to probe regimes of large ratios of outer to inner disc edge radii that are realistic for binary systems of hundreds of astronomical unit separations and are not easily probed by multidimensional simulations. For order unity binary mass ratios, KL instability is possible for a window of disc aspect ratios H/r in the outer parts of a disc that roughly scale as (nb/n)2 ≲ H/r ≲ nb/n, for binary orbital frequency nb and orbital frequency n at the disc outer edge. We present a framework for understanding the zones of instability based on the determination of branches of marginally unstable modes. In general, multiple growing eccentric KL modes can be present in a disc. Coplanar apsidal-nodal precession resonances delineate instability branches. We determine the range of tilt angles for unstable modes as a function of disc aspect ratio. Unlike the KL instability for free particles that involves a critical (minimum) tilt angle, disc instability is possible for any non-zero tilt angle depending on the disc aspect ratio.

  2. Dynamical instabilities in disc-planet interactions

    NASA Astrophysics Data System (ADS)

    Lin, Min-Kai

    2012-03-01

    Protoplanetary discs may become dynamically unstable due to structure induced by an embedded giant planet. In this thesis, I discuss the stability of such systems and explore the consequence of instability on planetary migration. I begin with non-self-gravitating, low viscosity discs and show that giant planets induce shocks inside its co-orbital region, leading to a profile unstable to vortex formation around a potential vorticity minimum. This instability is commonly known as the vortex or Rossby wave instability. Vortex-planet interaction lead to episodic phases of migration, which can be understood in the framework of type III migration. I then examine the effect of disc self-gravity on gap stability. The linear theory of the Rossby wave instability is extended to include disc gravity, which shows that self-gravity is effective at stabilising the vortex instability at small azimuthal wavenumber. This is consistent with the observation that more vortices develop with increasing disc mass in hydrodynamic simulations. Vortices in self-gravitating discs also resist merging, and is most simply understood as pair-vortices undergoing mutual horsehoe turns upon encounter. I show that in sufficiently massive discs vortex modes are suppressed. Instead, global spiral instabilities develop which are associated with a potential vorticity maximum at the gap edge. These edge modes can be physically understood as a result of unstable interaction between the gap edge and the exterior disc through gravity. I show the spiral arms can provide a positive torque on the planet, leading to fast migration outwards. I confirm the above results, obtained from razor-thin disc models, persist in three-dimensions.

  3. Ion dynamics and the magnetorotational instability in weakly ionized discs

    NASA Astrophysics Data System (ADS)

    Pandey, B. P.; Wardle, Mark

    2006-09-01

    The magnetorotational instability (MRI) of a weakly ionized, differentially rotating, magnetized plasma disc is investigated in the multifluid framework. The disc is threaded by a uniform vertical magnetic field and charge is carried by electrons and ions only. The inclusion of ion inertia causes significant modification to the conductivity tensor in a weakly ionized disc. The parallel, Pedersen and Hall component of conductivity tensor becomes time-dependent quantities resulting in ac and dc components of the conductivity. The time dependence of the conductivity causes significant modification to the parameter window of MRI. The effect of ambipolar and Hall diffusion on the linear growth of the MRI is examined in the presence of time-dependent conductivity tensor. We find that the growth rate in the ambipolar regime can become somewhat larger than the rotational frequency, especially when the departure from ideal magnetohydrodynamics (MHD) is significant. Further, the instability operates on large scalelengths. This has important implication for angular momentum transport in the disc. When charged grains are the dominant ions, their inertia will play important role near the mid-plane of the protoplanetary discs. Ion inertia could also be important in transporting angular momentum in accretion discs around compact objects, in cataclysmic variables. For example, in cataclysmic variables, where mass flows from a companion main-sequence star on to a white dwarf, the ionization fraction in the disc can vary in a wide range. The ion inertial effect in such a disc could significantly modify the MRI and therefore this instability could be a possible driver of the observed turbulent motion.

  4. Circumplanetary discs around young giant planets: a comparison between core-accretion and disc instability

    NASA Astrophysics Data System (ADS)

    Szulágyi, J.; Mayer, L.; Quinn, T.

    2017-01-01

    Circumplanetary discs can be found around forming giant planets, regardless of whether core accretion or gravitational instability built the planet. We carried out state-of-the-art hydrodynamical simulations of the circumplanetary discs for both formation scenarios, using as similar initial conditions as possible to unveil possible intrinsic differences in the circumplanetary disc mass and temperature between the two formation mechanisms. We found that the circumplanetary discs' mass linearly scales with the circumstellar disc mass. Therefore, in an equally massive protoplanetary disc, the circumplanetary discs formed in the disc instability model can be only a factor of 8 more massive than their core-accretion counterparts. On the other hand, the bulk circumplanetary disc temperature differs by more than an order of magnitude between the two cases. The subdiscs around planets formed by gravitational instability have a characteristic temperature below 100 K, while the core-accretion circumplanetary discs are hot, with temperatures even greater than 1000 K when embedded in massive, optically thick protoplanetary discs. We explain how this difference can be understood as the natural result of the different formation mechanisms. We argue that the different temperatures should persist up to the point when a full-fledged gas giant forms via disc instability; hence, our result provides a convenient criterion for observations to distinguish between the two main formation scenarios by measuring the bulk temperature in the planet vicinity.

  5. Characterizing gravitational instability in turbulent multicomponent galactic discs

    NASA Astrophysics Data System (ADS)

    Agertz, Oscar; Romeo, Alessandro B.; Grisdale, Kearn

    2015-05-01

    Gravitational instabilities play an important role in galaxy evolution and in shaping the interstellar medium (ISM). The ISM is observed to be highly turbulent, meaning that observables like the gas surface density and velocity dispersion depend on the size of the region over which they are measured. In this work, we investigate, using simulations of Milky Way-like disc galaxies with a resolution of ˜ 9 pc, the nature of turbulence in the ISM and how this affects the gravitational stability of galaxies. By accounting for the measured average turbulent scalings of the density and velocity fields in the stability analysis, we can more robustly characterize the average level of stability of the galaxies as a function of scale, and in a straightforward manner identify scales prone to fragmentation. Furthermore, we find that the stability of a disc with feedback-driven turbulence can be well described by a `Toomre-like' Q stability criterion on all scales, whereas the classical Q can formally lose its meaning on small scales if violent disc instabilities occur in models lacking pressure support from stellar feedback.

  6. Hall diffusion and the magnetorotational instability in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Wardle, Mark; Salmeron, Raquel

    2012-06-01

    The destabilizing effect of Hall diffusion in a weakly ionized Keplerian disc allows the magnetorotational instability (MRI) to occur for much lower ionization levels than would otherwise be possible. However, simulations incorporating Hall and Ohm diffusion give the impression that the consequences of this for the non-linear saturated state are not as significant as suggested by the linear instability. Close inspection reveals that this is not actually the case as the simulations have not yet probed the Hall-dominated regime. Here we revisit the effect of Hall diffusion on the MRI and the implications for the extent of magnetohydrodynamic (MHD) turbulence in protoplanetary discs, where Hall diffusion dominates over a large range of radii. We conduct a local, linear analysis of the instability for a vertical, weak magnetic field subject to axisymmetric perturbations with a purely vertical wave vector. In contrast to previous analyses, we express the departure from ideal MHD in terms of Hall and Pedersen diffusivities ηH and ηP, which provide transparent notation that is directly connected to the induction equation. This allows us to present a crisp overview of the dependence of the instability on magnetic diffusivity. We present analytic expressions and contours in the ηH-ηP plane for the maximum growth rate and corresponding wavenumber, the upper cut-off for unstable wavenumbers and the loci that divide the plane into regions of different characteristic behaviour. We find that for ?, where vA is the Alfvén speeds and Ω is the Keplerian frequency, Hall diffusion suppresses the MRI irrespective of the value of ηP. In the highly diffusive limit, the magnetic field decouples from the fluid perturbations and simply diffuses in the background Keplerian shear flow. The diffusive MRI reduces to a diffusive plane-parallel shear instability with effective shear rate (3/2)Ω. We give simple analytic expressions for the growth rate and wavenumber of the most unstable

  7. Bulge Growth Through Disc Instabilities in High-Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bournaud, Frédéric

    The role of disc instabilities, such as bars and spiral arms, and the associated resonances, in growing bulges in the inner regions of disc galaxies have long been studied in the low-redshift nearby Universe. There it has long been probed observationally, in particular through peanut-shaped bulges (Chap. 14 10.1007/978-3-319-19378-6_14"). This secular growth of bulges in modern disc galaxies is driven by weak, non-axisymmetric instabilities: it mostly produces pseudobulges at slow rates and with long star-formation timescales. Disc instabilities at high redshift (z > 1) in moderate-mass to massive galaxies (1010 to a few 1011 M⊙ of stars) are very different from those found in modern spiral galaxies. High-redshift discs are globally unstable and fragment into giant clumps containing 108-9 M⊙ of gas and stars each, which results in highly irregular galaxy morphologies. The clumps and other features associated to the violent instability drive disc evolution and bulge growth through various mechanisms on short timescales. The giant clumps can migrate inward and coalesce into the bulge in a few 108 years. The instability in the very turbulent media drives intense gas inflows toward the bulge and nuclear region. Thick discs and supermassive black holes can grow concurrently as a result of the violent instability. This chapter reviews the properties of high-redshift disc instabilities, the evolution of giant clumps and other features associated to the instability, and the resulting growth of bulges and associated sub-galactic components.

  8. MRI turbulence and thermal instability in accretion discs

    NASA Astrophysics Data System (ADS)

    Ross, Johnathan; Latter, Henrik N.; Tehranchi, Michael

    2017-06-01

    A long-standing puzzle in the study of black hole accretion concerns the presence or not of thermal instability. Classical theory predicts that the encircling accretion disc is unstable, as do some self-consistent magnetohydrodynamic simulations of the flow. Yet observations of strongly accreting sources generally fail to exhibit cyclic or unstable dynamics on the expected time-scales. This paper checks whether turbulent fluctuations impede thermal instability. It also asks if it makes sense to conduct linear stability analyses on a turbulent background. These issues are explored with a set of MRI simulations in thermally unstable local boxes in combination with stochastic equations that approximate the disc energetics. These models show that the disc's thermal behaviour deviates significantly from laminar theory, though ultimately a thermal runaway does occur. We find that the disc temperature evolves as a biased random walk, rather than increasing exponentially, and thus generates a broad spread of outcomes, with instability often delayed for several thermal times. We construct a statistical theory that describes some of this behaviour, emphasizing the importance of the 'escape time' and its associated probability distribution. In conclusion, turbulent fluctuations on their own cannot stabilize a disc, but they can weaken and delay thermal instability.

  9. On the vertical-shear instability in astrophysical discs

    NASA Astrophysics Data System (ADS)

    Barker, A. J.; Latter, H. N.

    2015-06-01

    We explore the linear stability of astrophysical discs exhibiting vertical shear, which arises when there is a radial variation in the temperature or entropy. Such discs are subject to a `vertical-shear instability', which recent non-linear simulations have shown to drive hydrodynamic activity in the MRI-stable regions of protoplanetary discs. We first revisit locally isothermal discs using the quasi-global reduced model derived by Nelson et al. This analysis is then extended to global axisymmetric perturbations in a cylindrical domain. We also derive and study a reduced model describing discs with power-law radial entropy profiles (`locally polytropic discs'), which are somewhat more realistic in that they possess physical (as opposed to numerical) surfaces. The fastest growing modes have very short wavelengths and are localized at the disc surfaces (if present), where the vertical shear is maximal. An additional class of modestly growing vertically global body modes is excited, corresponding to destabilized classical inertial waves (`r modes'). We discuss the properties of both types of modes, and stress that those that grow fastest occur on the shortest available length-scales (determined either by the numerical grid or the physical viscous length). This ill-posedness makes simulations of the instability difficult to interpret. We end with some brief speculation on the non-linear saturation and resulting angular momentum transport.

  10. The magnetic Rayleigh-Taylor instability in astrophysical discs

    NASA Astrophysics Data System (ADS)

    Contopoulos, I.; Kazanas, D.; Papadopoulos, D. B.

    2016-10-01

    This is our first study of the magnetic Rayleigh-Taylor instability at the inner edge of an astrophysical disc around a central back hole. We derive the equations governing small-amplitude oscillations in general relativistic ideal magnetodydrodynamics and obtain a criterion for the onset of the instability. We suggest that static disc configurations where magnetic field is held by the disc material are unstable around a Schwarzschild black hole. On the other hand, we find that such configurations are stabilized by the space-time rotation around a Kerr black hole. We obtain a crude estimate of the maximum amount of poloidal magnetic flux that can be accumulated around the centre, and suggest that it is proportional to the black hole spin. Finally, we discuss the astrophysical implications of our result for the theoretical and observational estimations of the black hole jet power.

  11. The Magnetic Rayleigh-Taylor Instability in Astrophysical Discs

    NASA Technical Reports Server (NTRS)

    Contopoulos, I.; Kazanas, D.; Papadopoulos, D. B.

    2016-01-01

    This is our first study of the magnetic Rayleigh-Taylor instability at the inner edge of an astrophysical disc around a central back hole. We derive the equations governing small-amplitude oscillations in general relativistic ideal magnetodydrodynamics and obtain a criterion for the onset of the instability. We suggest that static disc configurations where magnetic field is held by the disc material are unstable around a Schwarzschild black hole. On the other hand, we find that such configurations are stabilized by the space-time rotation around a Kerr black hole. We obtain a crude estimate of the maximum amount of poloidal magnetic flux that can be accumulated around the centre, and suggest that it is proportional to the black hole spin. Finally, we discuss the astrophysical implications of our result for the theoretical and observational estimations of the black hole jet power.

  12. An Analysis of Burst Disc Pressure Instability

    SciTech Connect

    S. L. Robinson; B. C. Odegard, Jr.; N. r. Moody; S. H. Goods

    2000-06-01

    During the development stage of the 1X Acorn burst disc, burst pressure test results exhibited an unexpected increase of 8 to 14% over times of 90--100 days from initial fabrication. This increase is a concern where design constraints require stability. The disc material, 316L stainless steel sheet, is formed to a dome-like geometry and scored to produce a thin-walled, high-strength ligament. The fracture events controlling burst occur in that ligament. Thus it has been characterized both for tensile properties and microstructure through nanoindentation, magnetic measurements, optical and transmission electron microscopy. These results compare favorably with finite element simulation of the properties of the ligament. The ligament exhibits a highly heterogeneous microstructure; its small volume and microstructural heterogeneity make it difficult to identify which microstructural feature controls fracture and hence burst pressure. Bulk mechanical test specimens were fabricated to emulate mid-ligament properties, and aged at both room and elevated temperatures to characterize and accelerate the temporal behavior of the burst disc. Property changes included yield and ultimate tensile strength increases, and fracture strain decreases with aging. Specimens were subjected to a reversion anneal identical to that given the burst disc to eliminate the martensite phase formed during rolling. Reversion-annealed samples exhibited no change in properties in room temperature or accelerated aging, showing that the reversion-anneal eliminated the aging phenomenon. Aging was analyzed in terms of diffusion controlled precipitate growth kinetics, showing that carbon migration to dislocations is consistent with the strength increases. A vacancy-assisted diffusion mechanism for carbon transport is proposed, giving rise to rapid aging, which replaces interstitial carbon diffusion until excess vacancies from deformation are consumed. Mechanical activation parameters in stress relaxation

  13. On dust-gas gravitational instabilities in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Latter, Henrik N.; Rosca, Roxana

    2017-01-01

    In protoplanetary discs the aerodynamical friction between particles and gas induces a variety of instabilities that facilitate planet formation. Of these we examine the so-called `secular gravitational instability' (SGI) in the two-fluid approximation, deriving analytical expressions for its stability criteria and growth rates. Concurrently, we present a physical explanation of the instability that shows how it manifests upon an intermediate range of lengthscales exhibiting geostrophic balance in the gas component. The two-fluid SGI is completely quenched within a critical disc radius, as large as 10 au and 30 au for centimetre- and millimetre-sized particles, respectively, although establishing robust estimates is hampered by uncertainties in the parameters (especially the strength of turbulence) and deficiencies in the razor-thin disc model we employ. It is unlikely, however, that the SGI is relevant for well-coupled dust. We conclude by applying these results to the question of planetesimal formation and the provenance of large-scale dust rings.

  14. Compressive vs Solenoidal Turbulence and Violent Disc Instability

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  15. Stellar motion induced by gravitational instabilities in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Michael, Scott; Durisen, R. H.

    2010-07-01

    We test the effect of assumptions about stellar motion on the behaviour of gravitational instabilities (GIs) in protoplanetary discs around solar-type stars by performing two simulations that are identical in all respects except the treatment of the star. In one simulation, the star is assumed to remain fixed at the centre of the inertial reference frame. In the other, stellar motion is handled properly by including an indirect potential in the hydrodynamic equations to model the star's reference frame as one which is accelerated by star/disc interactions. The discs in both simulations orbit a solar mass star, initially extend from 2.3 to 40 au with a ϖ-1/2 surface density profile, and have a total mass of 0.14 Msolar. The γ = 5/3 ideal gas is assumed to cool everywhere with a constant cooling time of two outer rotation periods. The overall behaviour of the disc evolution is similar, except for weakening in various measures of GI activity by about at most tens of per cent for the indirect potential case. Overall conclusions about disc evolution in earlier papers by our group, where the star was always assumed to be fixed in an inertial frame, remain valid. There is no evidence for independent one-armed instabilities, like the Stimulation by the Long-range Interaction of Newtonian Gravity (SLING), in either simulation. On the other hand, the stellar motion about the system centre of mass (COM) in the simulation with the indirect potential is substantial, up to 0.25 au during the burst phase, as GIs initiate, and averaging about 0.9 au during the asymptotic phase, when the GIs reach an overall balance of heating and cooling. These motions appear to be a stellar response to non-linear interactions between discrete global spiral modes in both the burst and asymptotic phases of the evolution, and the star's orbital motion about the COM reflects the orbit periods of disc material near the corotation radii of the dominant spiral waves. This motion is, in principle

  16. Streaming instability in the quasi-global protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Kowalik, K.; Hanasz, M.; Wóltański, D.; Gawryszczak, A.

    2013-09-01

    We investigate streaming instability using two-fluid approximation (neutral gas and dust) in a quasi-global, unstratified protoplanetary disc, with the help of PIERNIK code. We compare amplification rate of the eigenmode in numerical simulations, with the corresponding growth resulting from the linear stability analysis of full system of Euler's equation including aerodynamic drag. Following Youdin & Goodman (2005), we show that (1) rapid dust clumping occurs due to the difference in azimuthal velocities of gas and dust, coupled by the drag force, (2) initial density perturbations are amplified by several orders of magnitude. We demonstrate that the multifluid extension of the simple and efficient Relaxing TVD scheme, implemented in PIERNIK, leads to results, which are compatible with those obtained with other methods.

  17. Modal analysis of gravitational instabilities in nearly Keplerian, counter-rotating collisionless discs

    NASA Astrophysics Data System (ADS)

    Gulati, Mamta; Saini, Tarun Deep

    2017-02-01

    We present a modal analysis of instabilities of counter-rotating, self-gravitating collisionless stellar discs, using the recently introduced modified WKB formulation of spiral density waves for collisionless systems by Gulati & Saini. The discs are assumed to be axisymmetric and in coplanar orbits around a massive object at the common centre of the discs. The mass in both discs is assumed to be much smaller than the mass of the central object. For each disc, the disc particles are assumed to be in near circular orbits. The two discs are coupled to each other gravitationally. The perturbed dynamics of the discs evolves on the order of the precession time-scale of the discs, which is much longer than the Keplerian time-scale. We present results for the azimuthal wavenumber m = 1 and 2, for the full range of disc mass ratio between the prograde and retrograde discs. The eigenspectra are in general complex, therefore all eigenmodes are unstable. Eigenfunctions are radially more compact for m = 1 as compared to m = 2. Pattern speed of eigenmodes is always prograde with respect to the more massive disc. The growth rate of unstable modes increases with increasing mass fraction in the retrograde disc, and decreases with m; therefore, m = 1 instability is likely to play the dominant role in the dynamics of such systems.

  18. Non-linear violent disc instability with high Toomre's Q in high-redshift clumpy disc galaxies

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    We utilize zoom-in cosmological simulations to study the nature of violent disc instability in clumpy galaxies at high redshift, z = 1-5. Our simulated galaxies are not in the ideal state assumed in Toomre instability, of linear fluctuations in an isolated, uniform, rotating disc. There, instability is characterized by a Q parameter below unity, and lower when the disc is thick. Instead, the high-redshift discs are highly perturbed. Over long periods they consist of non-linear perturbations, compact massive clumps and extended structures, with new clumps forming in interclump regions. This is while the galaxy is subject to frequent external perturbances. We compute the local, two-component Q parameter for gas and stars, smoothed on a ˜1 kpc scale to capture clumps of 108-9 M⊙. The Q < 1 regions are confined to collapsed clumps due to the high surface density there, while the interclump regions show Q significantly higher than unity. Tracing the clumps back to their relatively smooth Lagrangian patches, we find that Q prior to clump formation typically ranges from unity to a few. This is unlike the expectations from standard Toomre instability. We discuss possible mechanisms for high-Q clump formation, e.g. rapid turbulence decay leading to small clumps that grow by mergers, non-axisymmetric instability, or clump formation induced by non-linear perturbations in the disc. Alternatively, the high-Q non-linear VDI may be stimulated by the external perturbations such as mergers and counter-rotating streams. The high Q may represent excessive compressive modes of turbulence, possibly induced by tidal interactions.

  19. Gravitoturbulence and the excitation of small-scale parametric instability in astrophysical discs

    NASA Astrophysics Data System (ADS)

    Riols, A.; Latter, H.; Paardekooper, S.-J.

    2017-10-01

    Young protoplanetary discs and the outer radii of active galactic nuclei may be subject to gravitational instability and, as a consequence, fall into a 'gravitoturbulent' state. While in this state, appreciable angular momentum can be transported; alternatively, the gas may collapse into bound clumps, the progenitors of planets or stars. In this paper, we numerically characterize the properties of 3D gravitoturbulence, focusing especially on its dependence on numerical parameters (resolution, domain size) and its excitation of small-scale dynamics. Via a survey of vertically stratified shearing-box simulations with pluto and rodeo, we find (a) evidence that certain gravitoturbulent properties are independent of horizontal box size only when the box is larger than ≃40H, where H is the scaleheight, (b) at high resolution, small-scale isotropic turbulence appears off the mid-plane around z ≃ 0.5-1H and (c) this small-scale dynamics results from a parametric instability, involving the coupling of inertial waves with a large-scale axisymmetric epicyclic mode. This mode oscillates at a frequency close to Ω and is naturally excited by gravitoturbulence via a non-linear process to be determined. The small-scale turbulence we uncover has potential implications for a wide range of disc physics, e.g. turbulent saturation levels, fragmentation, turbulent mixing and dust settling.

  20. Supermassive star formation via episodic accretion: protostellar disc instability and radiative feedback efficiency

    NASA Astrophysics Data System (ADS)

    Sakurai, Y.; Vorobyov, E. I.; Hosokawa, T.; Yoshida, N.; Omukai, K.; Yorke, H. W.

    2016-06-01

    The formation of supermassive stars (SMSs) is a potential pathway to seed supermassive black holes in the early universe. A critical issue for forming SMSs is stellar UV feedback, which may limit the stellar mass growth via accretion. In this paper, we study the evolution of an accreting SMS and its UV emissivity with realistic variable accretion from a circumstellar disc. First we conduct a 2D hydrodynamical simulation to follow the protostellar accretion until the stellar mass exceeds 104 M⊙. The disc fragments by gravitational instability, creating many clumps that migrate inward to fall on to the star. The resulting accretion history is highly time-dependent: short episodic accretion bursts are followed by longer quiescent phases. We show that the disc for the direct collapse model is more unstable and generates greater variability than normal Pop III cases. Next, we conduct a stellar evolution calculation using the obtained accretion history. Our results show that, regardless of the variable accretion, the stellar radius monotonically increases with almost constant effective temperature at Teff ≃ 5000 K as the stellar mass increases. The resulting UV feedback is too weak to hinder accretion due to the low flux of stellar UV photons. The insensitivity of stellar evolution to variable accretion is attributed to the fact that time-scales of variability, ≲103 yr, are too short to affect the stellar structure. We argue that this evolution will continue until the SMS collapses to produce a black hole by the general relativistic instability after the mass reaches ≳105 M⊙.

  1. Vortex and spiral instabilities at gap edges in three-dimensional self-gravitating disc-satellite simulations

    NASA Astrophysics Data System (ADS)

    Lin, Min-Kai

    2012-11-01

    Numerical simulations of global three-dimensional (3D), self-gravitating discs with a gap opened by an embedded planet are presented. The simulations are customized to examine planetary gap stability. Previous results, obtained by Lin & Papaloizou from 2D disc models, are reproduced in 3D. These include (i) the development of vortices associated with local vortensity minima at gap edges and their merging on dynamical time-scales in weakly self-gravitating discs, (ii) the increased number of vortices as the strength of self-gravity is increased and their resisted merging, and (iii) suppression of the vortex instability and development of global spiral arms associated with local vortensity maxima in massive discs. The vertical structure of these disturbances is examined. In terms of the relative density perturbation, the vortex disturbance has weak vertical dependence when self-gravity is neglected. Vortices become more vertically stratified with increasing self-gravity. This effect is seen even when the unperturbed region around the planet's orbital radius has a Toomre stability parameter ˜10. The spiral modes display significant vertical structure at the gap edge, with the mid-plane density enhancement being several times larger than that near the upper disc boundary. However, for both instabilities the vertical Mach number is typically a few per cent, and on average vertical motions near the gap edge do not dominate horizontal motions.

  2. Dependence of optic disc parameters on disc area according to Heidelberg Retina Tomograph: Part II.

    NASA Astrophysics Data System (ADS)

    Machekhin, V.; Manaenkova, G.; Bondarenko, O.

    2007-05-01

    With the help of Heidelberg Retina Tomograph (HRT-II) optic disc parameters in 211 eyes of 115 healthy patients with refraction Em +/- 3,0 D and 96 eyes of 72 patients with myopia 3,5-14,0 D without any signs of glaucoma were studied. Analysis of optic disc parameters were carried out in 5 groups of patients according to disc area: less than 1,5 mm2, 1,5- 2,5 mm2, 2,5-3,0 mm2, 3,0-3,5 mm2 and more than 3,5 mm2. An accurate depending on disc area was revealed for all optic disc parameters in all sectors, which was manifested by increasing cup disc and rim disc (area and volume) and other parameters. We consider it is necessary to use the proper tables for right interpretation of received data for early diagnosis of glaucoma.

  3. The role of gap edge instabilities in setting the depth of planet gaps in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Hallam, P. D.; Paardekooper, S.-J.

    2017-08-01

    It is known that an embedded massive planet will open a gap in a protoplanetary disc via angular momentum exchange with the disc material. The resulting surface density profile of the disc is investigated for one-dimensional and two-dimensional disc models and, in agreement with previous work, it is found that one-dimensional gaps are significantly deeper than their two-dimensional counterparts for the same initial conditions. We find, by applying one-dimensional torque density distributions to two-dimensional discs containing no planet, that the excitement of the Rossby wave instability and the formation of Rossby vortices play a critical role in setting the equilibrium depth of the gap. Being a two-dimensional instability, this is absent from one-dimensional simulations and does not limit the equilibrium gap depth there. We find similar gap depths between two-dimensional gaps formed by torque density distributions, in which the Rossby wave instability is present, and two-dimensional planet gaps, in which no Rossby wave instability is present. This can be understood if the planet gap is maintained at marginal stability, even when there is no obvious Rossby wave instability present. Further investigation shows the final equilibrium gap depth is very sensitive to the form of the applied torque density distribution, and using improved one-dimensional approximations from three-dimensional simulations can go even further towards reducing the discrepancy between one- and two-dimensional models, especially for lower mass planets. This behaviour is found to be consistent across discs with varying parameters.

  4. Gravitational instabilities in a protosolar-like disc - II. Continuum emission and mass estimates

    NASA Astrophysics Data System (ADS)

    Evans, M. G.; Ilee, J. D.; Hartquist, T. W.; Caselli, P.; Szűcs, L.; Purser, S. J. D.; Boley, A. C.; Durisen, R. H.; Rawlings, J. M. C.

    2017-09-01

    Gravitational instabilities (GIs) are most likely a fundamental process during the early stages of protoplanetary disc formation. Recently, there have been detections of spiral features in young, embedded objects that appear consistent with GI-driven structure. It is crucial to perform hydrodynamic and radiative transfer simulations of gravitationally unstable discs in order to assess the validity of GIs in such objects, and constrain optimal targets for future observations. We utilize the radiative transfer code lime (Line modelling Engine) to produce continuum emission maps of a 0.17 M⊙ self-gravitating protosolar-like disc. We note the limitations of using lime as is and explore methods to improve upon the default gridding. We use casa to produce synthetic observations of 270 continuum emission maps generated across different frequencies, inclinations and dust opacities. We find that the spiral structure of our protosolar-like disc model is distinguishable across the majority of our parameter space after 1 h of observation, and is especially prominent at 230 GHz due to the favourable combination of angular resolution and sensitivity. Disc mass derived from the observations is sensitive to the assumed dust opacities and temperatures, and therefore can be underestimated by a factor of at least 30 at 850 GHz and 2.5 at 90 GHz. As a result, this effect could retrospectively validate GIs in discs previously thought not massive enough to be gravitationally unstable, which could have a significant impact on the understanding of the formation and evolution of protoplanetary discs.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  6. The behavior of magnetic Prandtl number on the Rossby wave instability in the protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Gholipour, Mahmoud; Ebadi, Hossein; Shaji, Zeynab

    2017-07-01

    In recent years, the Rossby wave instability (RWI) has become the target of intense theoretical and simulation investigations in dealing to some ambiguous problems such as the planet formation and angular momentum transport in the protoplanetary discs. The role of hydrodynamic turbulence on the RWI theory has been well understood by many theoretical and simulation works. However, less attention has been paid to the magnetohydrodynamic (MHD) turbulence in theoretical works related to the RWI. However, the turbulent magnetic Prandtl numbers (Prm), i.e., the ratio of the turbulent viscosity to the turbulent magnetic diffusivity, is one of the significant parameters in (MHD) turbulence. On the other hand, the gradient and strength of the toroidal magnetic field can affect some variables and parameters in the stationary and perturbation states in some radii which may be lead to important results. In this paper, the whole range of Prm is considered in details with considering the gradient and strength of the toroidal magnetic field. Although complicating the problem, it gives us a comprehensive view on the RWI occurrence in the cold and hot discs. The results show that the Prm can significantly control the RWI occurrence as well as the growth rate of unstable modes. While the magneto-rotational instability cannot be responsible for the angular momentum transport in the protoplanetary discs, our results indicate that the RWI is responsible about this subject in these discs.

  7. Thermal instabilities in cooling galactic coronae: fuelling star formation in galactic discs

    NASA Astrophysics Data System (ADS)

    Hobbs, Alexander; Read, Justin; Power, Chris; Cole, David

    2013-09-01

    We investigate the means by which cold gas can accrete on to Milky Way mass galaxies from a hot corona of gas, using a new smoothed particle hydrodynamics code, `SPHS'. We find that the `cold clumps' seen in many classic SPH simulations in the literature are not present in our SPHS simulations. Instead, cold gas condenses from the halo along filaments that form at the intersection of supernovae-driven bubbles from previous phases of star formation. This positive feedback feeds cold gas to the galactic disc directly, fuelling further star formation. The resulting galaxies in the SPH and SPHS simulations differ greatly in their morphology, gas phase diagrams and stellar content. We show that the classic SPH cold clumps owe to a numerical thermal instability caused by an inability for cold gas to mix in the hot halo. The improved treatment of mixing in SPHS suppresses this instability leading to a dramatically different physical outcome. In our highest resolution SPHS simulation, we find that the cold filaments break up into bound, physically motivated clumps that form stars. The filaments are overdense by a factor of 10-100 compared to the surrounding gas, suggesting that the fragmentation results from a physical non-linear instability driven by the overdensity. This `fragmenting filament' mode of disc growth has important implications for galaxy formation, in particular the role of star formation in bringing cold gas into disc galaxies.

  8. The biomechanics of lumbar disc herniation and the effect of overload and instability.

    PubMed

    Wilder, D G; Pope, M H; Frymoyer, J W

    1988-01-01

    A multipart study has been performed to provide a mechanical explanation for the epidemiologic association between sitting in static (e.g., factory or office) or vibration (e.g., car or truck driving) environments and acute herniated lumbar discs. It was shown that a 1 h exposure to sitting environments caused significant changes in the mechanical properties of the lumbar intervertebral disc. During many of the latter tests, specimens were unstable (exhibited by a sudden, large flexion and/or lateral bend rotation response to an axially applied load). This showed that a motion segment in the lumbar spine could suddenly buckle and apply a tensile impact loading to the posterolateral region of the disc. We also demonstrated that a combined lateral bend, flexion, and axial rotation vibration loading could cause tracking tears proceeding from the nucleus through the posterolateral region of the anulus. It suggests that a mechanism for disc herniation is mechanical changes leading to instability of the motion segment. These experiments complete the argument that lumbar disc herniations can be a direct mechanical consequence of prolonged sitting in static or vibration environments.

  9. Particle dynamics in discs with turbulence generated by the vertical shear instability

    NASA Astrophysics Data System (ADS)

    Stoll, Moritz H. R.; Kley, Wilhelm

    2016-10-01

    Context. Among the candidates for generating turbulence in accretion discs in situations with low intrinsic ionization, the vertical shear instability (VSI) has become an interesting candidate, since it relies purely on a vertical gradient in the angular velocity. Existing numerical simulations have shown that α-values a few times 10-4 can be generated. Aims: The particle growth in the early planet formation phase is determined by the dynamics of embedded dust particles. Here, we address, in particular, the efficiency of VSI-turbulence in concentrating particles to generate overdensities and low collision velocities. Methods: We perform three-dimensional (3D) numerical hydrodynamical simulations of accretion discs around young stars that include radiative transport and irradiation from the central star. The motion of embedded particles within a size range of a fraction of mm up to several m is followed using standard drag formula. Results: We confirm that, under realistic conditions, the VSI is able to generate turbulence in full 3D protoplanetary discs. The irradiated disc shows turbulence within 10 to 60 au. The mean radial motion of the gas is such that it is directed inward near the midplane and outward in the surface layers. We find that large particles drift inward with the expected speed, while small particles can experience phases of outward drift. Additionally, the particles show bunching behaviour with overdensities reaching five times the average value, which is strongest for dimensionless stopping times around unity. Conclusions: Particles in a VSI-turbulent discs are concentrated in large-scale turbulent eddies and show low relative speeds that allow for growing collisions. The reached overdensities will also enable the onset of streaming instabilities, further enhancing particle growth. The outward drift for small particles at higher disk elevations enable the transport of processed high temperature material in the solar system to greater distances.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  11. Global behaviour corresponding to the absolute instability of the rotating-disc boundary layer

    NASA Astrophysics Data System (ADS)

    Davies, Christopher; Carpenter, Peter W.

    2003-07-01

    A study is carried out of the linear global behaviour corresponding to the absolute instability of the rotating-disc boundary layer. It is based on direct numerical simulations of the complete linearized Navier Stokes equations obtained with the novel velocity vorticity method described in Davies & Carpenter (2001). As the equations are linear, they become separable with respect to the azimuthal coordinate, theta. This permits us to simulate a single azimuthal mode. Impulse-like excitation is used throughout. This creates disturbances that take the form of wavepackets, initially containing a wide range of frequencies. When the real spatially inhomogeneous flow is approximated by a spatially homogeneous flow (the so-called parallel-flow approximation) the results ofthe simulations are fully in accordance with the theory of Lingwood (1995). If the flow parameters are such that her theory indicates convective behaviour the simulations clearly exhibit the same behaviour. And behaviour fully consistent with absolute instability is always found when the flow parameters lie within the theoretical absolutely unstable region. The numerical simulations of the actual inhomogeneous flow reproduce the behaviour seen in the experimental study of Lingwood (1996). In particular, there is close agreement between simulation and experiment for the ray paths traced out by the leading and trailing edges of the wavepackets. In absolutely unstable regions the short-term behaviour of the simulated disturbances exhibits strong temporal growth and upstream propagation. This is not sustained for longer times, however. The study suggests that convective behaviour eventually dominates at all the Reynolds numbers investigated, even for strongly absolutely unstable regions. Thus the absolute instability of the rotating-disc boundary layer does not produce a linear amplified global mode as observed in many other flows. Instead the absolute instability seems to be associated with transient

  12. Early formation of massive, compact, spheroidal galaxies with classical profiles by violent disc instability or mergers

    NASA Astrophysics Data System (ADS)

    Ceverino, Daniel; Dekel, Avishai; Tweed, Dylan; Primack, Joel

    2015-03-01

    We address the formation of massive stellar spheroids between redshifts z = 4 and 1 using a suite of adaptive mesh refinement hydrocosmological simulations. The spheroids form as bulges, and the spheroid mass growth is partly driven by violent disc instability (VDI) and partly by mergers. A kinematic decomposition to disc and spheroid yields that the mass fraction in the spheroid is between 50 and 90 per cent and is roughly constant in time, consistent with a cosmological steady state of VDI discs that are continuously fed from the cosmic web. The density profile of the spheroid is typically `classical', with a Sérsic index n = 4.5 ± 1, independent of whether it grew by mergers or VDI and independent of the feedback strength. The disc is characterized by n = 1.5 ± 0.5, and the whole galaxy by n = 3 ± 1. The high-redshift spheroids are compact due to the dissipative inflow of gas and the high universal density. The stellar surface density within the effective radius of each galaxy as it evolves remains roughly constant in time after its first growth. For galaxies of a fixed stellar mass, the surface density is higher at higher redshifts.

  13. Outbursts of EX Hydrae: mass-transfer events or disc instabilities?

    NASA Astrophysics Data System (ADS)

    Hellier, Coel; Kemp, Jonathan; Naylor, T.; Bateson, Frank M.; Jones, Albert; Overbeek, Danie; Stubbings, Rod; Mukai, Koji

    2000-04-01

    We present the 45-yr record of the light curve of EX Hya, and discuss the characteristics of its 15 observed outbursts. We then concentrate on the 1998 outburst, reporting the first outburst X-ray observations. We discover an X-ray beat-cycle modulation, indicating that an enhanced accretion stream couples directly with the magnetosphere in outburst, confirming our previous prediction. Optical eclipse profiles late in outburst show that the visible light is dominated by an enhanced mass-transfer stream overflowing the accretion disc. We are uncertain whether the enhanced mass transfer is triggered by a disc instability, or by some other cause. While in outburst, EX Hya shows some of the characteristics of SW Sex stars.

  14. Early evolution of clumps formed via gravitational instability in protoplanetary discs: precursors of Hot Jupiters?

    NASA Astrophysics Data System (ADS)

    Galvagni, M.; Mayer, L.

    2014-01-01

    Although it is fairly established that Gravitational Instability (GI) should occur in the early phases of the evolution of a protoplanetary disc, the fate of the clumps resulting from disc fragmentation and their role in planet formation is still unclear. In the present study we investigate semi-analytically their evolution following the contraction of a synthetic population of clumps with varied initial structure and orbits coupled with the surrounding disc and the central star. Our model is based on recently published state-of-the-art 3D collapse simulations of clumps with varied thermodynamics. Various evolutionary mechanisms are taken into account, and their effect is explored both individually and in combination with others: migration and tidal disruption, mass accretion, gap opening and disc viscosity. It is found that, in general, at least 50 per cent of the initial clumps survive tides, leaving behind potential gas giant progenitors after ˜105 yr of evolution in the disc. The rest might either be disrupted or produce super-Earths and other low-mass planets provided that a solid core can be assembled on a sufficiently short time-scale, a possibility that we do not address in this paper. Extrapolating to million year time-scales, all our surviving protoplanets would lead to close-in gas giants. This outcome might in part reflect the limitations of the migration model adopted, and is reminiscent of the analogous result found in core-accretion models in absence of fine-tuning of the migration rate. Yet it suggests that a significant fraction of the clumps formed by GI could be the precursors of Hot Jupiters.

  15. Global multifluid simulations of the magnetorotational instability in radially stratified protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Rodgers-Lee, D.; Ray, T. P.; Downes, T. P.

    2016-11-01

    The redistribution of angular momentum is a long standing problem in our understanding of protoplanetary disc (PPD) evolution. The magnetorotational instability (MRI) is considered a likely mechanism. We present the results of a study involving multifluid global simulations including Ohmic dissipation, ambipolar diffusion and the Hall effect in a dynamic, self-consistent way. We focus on the turbulence resulting from the non-linear development of the MRI in radially stratified PPDs and compare with ideal magnetohydrodynamics simulations. In the multifluid simulations, the disc is initially set up to transition from a weak Hall-dominated regime, where the Hall effect is the dominant non-ideal effect but approximately the same as or weaker than the inductive term, to a strong Hall-dominated regime, where the Hall effect dominates the inductive term. As the simulations progress, a substantial portion of the disc develops into a weak Hall-dominated disc. We find a transition from turbulent to laminar flow in the inner regions of the disc, but without any corresponding overall density feature. We introduce a dimensionless parameter, αRM, to characterize accretion with αRM ≳ 0.1 corresponding to turbulent transport. We calculate the eddy turnover time, teddy, and compared this with an effective recombination time-scale, trcb, to determine whether the presence of turbulence necessitates non-equilibrium ionization calculations. We find that trcb is typically around three orders of magnitude smaller than teddy. Also, the ionization fraction does not vary appreciably. These two results suggest that these multifluid simulations should be comparable to single-fluid non-ideal simulations.

  16. Field Dependence, Perceptual Instability, and Sex Differences.

    ERIC Educational Resources Information Center

    Bergum, Judith E.; Bergum, Bruce O.

    Recent studies have shown perceptual instability to be related to visual creativity as reflected in career choice. In general, those who display greater perceptual instability perceive themselves to be more creative and tend to choose careers related to visual creativity, regardless of their gender. To test the hypothesis that field independents…

  17. Two-stream instability with time-dependent drift velocity

    DOE PAGES

    Qin, Hong; Davidson, Ronald C.

    2014-06-26

    The classical two-stream instability driven by a constant relative drift velocity between two plasma components is extended to the case with time-dependent drift velocity. A solution method is developed to rigorously define and calculate the instability growth rate for linear perturbations relative to the time-dependent unperturbed two-stream motions. The stability diagrams for the oscillating two-stream instability are presented over a large region of parameter space. It is shown that the growth rate for the classical two-stream instability can be significantly reduced by adding an oscillatory component to the relative drift velocity.

  18. Shear instability in fluids with a density-dependent viscosity.

    PubMed

    Steinberg, V; Ivlev, A V; Kompaneets, R; Morfill, G E

    2008-06-27

    We present a shear instability, which can be triggered in compressible fluids with density-dependent viscosity at shear rates above critical. The instability mechanism is generic: It is based on density-dependent viscosity, compressibility, as well as flow two-(three-)dimensionality that provides coupling between streamwise and transversal velocity components and density variations. The only factor stabilizing the instability is fluid elasticity. The corresponding eigenvalue problem for a plane Couette flow is solved analytically in the limiting cases of large and small wave numbers.

  19. Inflammatory response of disc cells against Propionibacterium acnes depends on the presence of lumbar Modic changes.

    PubMed

    Dudli, Stefan; Miller, S; Demir-Deviren, S; Lotz, J C

    2017-09-07

    Intervertebral disc with Propionibacterium acnes (P. acnes) is suggested to be an etiology of Modic type I changes in the adjacent bone marrow. However it is unknown if disc cells can respond to P. acnes and if bone marrow cells respond to bacterial and disc metabolites draining from infected discs. Human disc cells (n = 10) were co-cultured with 10- and 100-fold excess of P. acnes over disc cells for 3 h and 24 h. Lipopolysaccharide was used as positive control. Expression of IL1, IL6, IL8, and CCL2 by disc cells was quantified by quantitative PCR. Lipase activity was measured in culture supernatants (n = 6). Human vertebral bone marrow mononuclear cells (BMNCs) (n = 2) were cultured in conditioned media from disc cell/P. acnes co-cultures and expression of IL1, IL6, IL8, and CCL2 was measured after 24 h. All disc cells responded to lipopolysaccharide but only 6/10 responded to P. acnes with increased cytokine expression. Cytokine increase was time- but not P. acnes concentration-dependent. Disc cell responsiveness was associated with the presence of lumbar Modic changes in the donor. Lipase activity was increased independent of disc cell responsiveness. BMNCs responded with inflammatory activity only when cultured in supernatants from responsive disc cell lines. Disc cell responsiveness to P. acnes associates with the presence of lumbar Modic changes. Furthermore, bone marrow cells had an inflammatory response to the cocktail of disc cytokines and P. acnes metabolites. These data indicate that low virulent P. acnes infection of the disc is a potential exacerbating factor to Modic changes.

  20. DISC1 in Astrocytes Influences Adult Neurogenesis and Hippocampus-Dependent Behaviors in Mice.

    PubMed

    Terrillion, Chantelle E; Abazyan, Bagrat; Yang, Zhongxi; Crawford, Joshua; Shevelkin, Alexey V; Jouroukhin, Yan; Yoo, Ki Hyun; Cho, Chang Hoon; Roychaudhuri, Robin; Snyder, Solomon H; Jang, Mi-Hyeon; Pletnikov, Mikhail V

    2017-10-01

    The functional role of genetic variants in glia in the pathogenesis of psychiatric disorders remains poorly studied. Disrupted-In-Schizophrenia 1 (DISC1), a genetic risk factor implicated in major mental disorders, has been implicated in regulation of astrocyte functions. As both astrocytes and DISC1 influence adult neurogenesis in the dentate gyrus (DG) of the hippocampus, we hypothesized that selective expression of dominant-negative C-terminus-truncated human DISC1 (mutant DISC1) in astrocytes would affect adult hippocampal neurogenesis and hippocampus-dependent behaviors. A series of behavioral tests were performed in mice with or without expression of mutant DISC1 in astrocytes during late postnatal development. In conjunction with behavioral tests, we evaluated adult neurogenesis, including neural progenitor proliferation and dendrite development of newborn neurons in the DG. The ameliorative effects of D-serine on mutant DISC1-associated behaviors and abnormal adult neurogenesis were also examined. Expression of mutant DISC1 in astrocytes decreased neural progenitor proliferation and dendrite growth of newborn neurons, and produced elevated anxiety, attenuated social behaviors, and impaired hippocampus-dependent learning and memory. Chronic treatment with D-serine ameliorated the behavioral alterations and rescued abnormal adult neurogenesis in mutant DISC1 mice. Our findings suggest that psychiatric genetic risk factors expressed in astrocytes could affect adult hippocampal neurogenesis and contribute to aspects of psychiatric disease through abnormal production of D-serine.

  1. Planetary migration in weakly magnetized turbulent discs

    NASA Astrophysics Data System (ADS)

    Baruteau, C.; Fromang, S.; Nelson, R. P.; Masset, F.

    2011-12-01

    In laminar viscous disc models, the migration of protoplanets embedded in their nascent protoplanetary discs may be directed inwards or outwards, depending on the relative magnitude of the Lindblad and corotation torques. The long-term evolution of the corotation torque is intimately related to diffusion processes inside the planet's horseshoe region. This communication examines the properties of the corotation torque in discs where magnetohydrodynamic (MHD) turbulence develops as a result of the magnetorotational instability (MRI), considering a weak initial toroidal magnetic field. We show that the differential Lindblad torque takes very similar values in MHD turbulent and laminar viscous discs, and there exists an unsaturated corotation torque in MHD turbulent discs.

  2. DISC1 as a Possible Genetic Contribution to Opioid Dependence in a Polish Sample

    PubMed Central

    Fudalej, Sylwia; Jakubczyk, Andrzej; Kopera, Maciej; Piwoński, Jerzy; Bielecki, Wojciech; Drygas, Wojciech; Wasilewska, Krystyna; Ilgen, Mark; Bohnert, Amy; Barry, Kristen; Płoski, Rafał; Blow, Frederic C.; Wojnar, Marcin

    2016-01-01

    Objective: Disrupted-in-schizophrenia 1 (DISC1) has been linked to vulnerability to a variety of psychiatric disorders and neuropsychiatric phenotypes. However, DISC1 has not been frequently examined as a potential risk factor for substance dependence. An association between opioid dependence and DISC1 rs2738888 polymorphism has been recently reported. In addition, opioid dependence was associated with rs6419156 located close to the protein phosphatase 3 catalytic subunit alpha isoform (PPP3CA) gene. The aim of the present study was to examine the associations between opioid dependence with rs2738888 and rs6419156 in an independent sample. Method: The selected polymorphisms were genotyped in a sample of 392 individuals (69.9% male) diagnosed as alcohol- and/or opioid-dependent. A control group (n = 257; 67.7% male) was derived from the Polish National Health Survey (N = 14,350). Results: The frequency of rs2738888 C allele was higher in controls than in opioid-dependent cases (OR = 0.65, p = .045). Phenotypic-oriented analyses performed within opioid-dependent individuals revealed the association between lifetime suicide attempt and rs2738888. The C allele of rs2738888 had a protective effect on lifetime suicide attempt in opioid-dependent patients (OR = 0.25, p = .003). Rs6419156 was not associated with substance dependence in the examined sample. Conclusions: The DISC1 may play an important role in vulnerability to opioid dependence. In addition, DISC1 may also be a genetic risk factor for suicide attempt in opioid-dependent individuals. PMID:26997180

  3. Viscous pulsational instability of the transonic region of isothermal geometrically thin accretion discs. I - Analytical results

    NASA Technical Reports Server (NTRS)

    Kato, Shoji; Honma, Fumio; Matsumoto, Ryoji

    1988-01-01

    Viscous instability of the transonic region of the conventional geometrically thin alpha-type accretion disks is examined analytically. For simplicity, isothermal disks and isothermal perturbations are assumed. It is found that when the value of alpha is larger than a critical value the disk is unstable against two types of perturbations. One is local propagating perturbations of inertial acoustic waves. Results suggest the possibility that unstable perturbations develop to overstable global oscillations which are restricted only in the innermost region of the disk. The other is standing growing perturbations localized just at the transonic point. The cause of these instabilities is that the azimuthal component of the Lagrangian velocity variation associated with the perturbations becomes in phase with the variation of the viscous stress force. Because of this phase matching work is done on perturbations, and they are amplified.

  4. Disc Dynamics In The Early Universe: Instabilities, Giant Clumps, Feedback & Outflows

    NASA Astrophysics Data System (ADS)

    Bournaud, Frédéric

    2016-10-01

    Star-forming galaxies at high redshift (z=1-3) have irregular, clumpy morphologies. These are best explained by a violent, ubiquitous gravitational instability in gas-rich disks, causing fragmentation in giant clumps and other irregular features. The instability can rapidly redistribute the baryons within galaxies, by inward migration of the giant clumps and other rapid inflows of mass. The promotes the growth of central bulges and other galactic components, and models predict that the resulting properties may finely match those observed in today's Milky Way-like spirals. The instability-driven inflow may also feed the central black hole in a moderate but steady mode and drive a high fraction of active galaxies, promoting earlier supermassive black hole growth. At the same time, intense stellar feedback in the giant gas-rich clumps and from the active nucleus drive intense gas outflows that regulate the galaxy mass to realistic levels, but the outflows are largely decoupled from the dense gas phases, which continue to form stars continuously. Hence the high-redshift progenitors of massive galaxies evolve in a steady unstable state lasting a couple of Gyr during which they build their fondamental structural components before evolving secularly into modern, quasi-stable spiral disks and spheroids.

  5. Dose-Dependent Response of Tissue-Engineered Intervertebral Discs to Dynamic Unconfined Compressive Loading

    PubMed Central

    Hudson, Katherine D.; Mozia, Robert I.

    2015-01-01

    Because of the limitations of current surgical methods in the treatment of degenerative disc disease, tissue-engineered intervertebral discs (TE-IVDs) have become an important target. This study investigated the biochemical and mechanical responses of composite TE-IVDs to dynamic unconfined compression. TE-IVDs were manufactured by floating an injection molded alginate nucleus pulposus (NP) in a type I collagen annulus fibrosus (AF) that was allowed to contract for 2 weeks before loading. The discs were mechanically stimulated at a range of strain amplitude (1–10%) for 2 weeks with a duty cycle of 1 h on–1 h off–1 h on before being evaluated for their biochemical and mechanical properties. Mechanical loading increased all properties in a dose-dependent manner. Glycosaminoglycans (GAGs) increased between 2.8 and 2.2 fold in the AF and NP regions, respectively, whereas the hydroxyproline content increased between 1.2 and 1.8 fold. The discs also experienced a 2-fold increase in the equilibrium modulus and a 4.3-fold increase in the instantaneous modulus. Full effects for all properties were seen by 5% strain amplitude. These data suggest that dynamic loading increases the functionality of our TE-IVDs with region-dependent responses using a method that may be scaled up to larger disc models to expedite maturation for implantation. PMID:25277703

  6. Analysis of the Relationship between Ligamentum Flavum Thickening and Lumbar Segmental Instability, Disc Degeneration, and Facet Joint Osteoarthritis in Lumbar Spinal Stenosis

    PubMed Central

    Yoshiiwa, Toyomi; Notani, Naoki; Ishihara, Toshinobu; Kawano, Masanori; Tsumura, Hiroshi

    2016-01-01

    Study Design Cross-sectional study. Purpose To investigate the relationship between ligamentum flavum (LF) thickening and lumbar segmental instability and disc degeneration and facet joint osteoarthritis. Overview of Literature Posterior spinal structures, including LF thickness, play a major role in lumbar spinal canal stenosis pathogenesis. The cause of LF thickening is multifactorial and includes activity level, age, and mechanical stress. LF thickening pathogenesis is unknown. Methods We examined 419 patients who underwent computed tomography (CT) myelography and magnetic resonance imaging after complaints of clinical symptoms. To investigate LF hypertrophy, 57 patients whose lumbar vertebra had normal disc heights at L4–5 were selected to exclude LF buckling as a hypertrophy component. LF thickness, disc space widening angulation in flexion, segmental angulation, presence of a vacuum phenomenon, and lumbar lordosis at T12–S1 were investigated. Disc and facet degeneration were also evaluated. Facet joint orientation was measured via an axial CT scan. Results The mean LF thickness in all patients was 4.4±1.0 mm at L4–5. There was a significant correlation between LF thickness and disc degeneration; LF thickness significantly increased with severe disc degeneration and facet joint osteoarthritis. There was a tendency toward increased LF thickness in more sagittalized facet joints than in coronalized facet joints. Logistic regression analysis showed that LF thickening was influenced by segmental angulation and facet joint osteoarthritis. Patient age was associated with LF thickening. Conclusions LF hypertrophy development was associated with segmental instability and severe disc degeneration, severe facet joint osteoarthritis, and a sagittalized facet joint orientation. PMID:27994791

  7. A unified approach for squeal instability analysis of disc brakes with two types of random-fuzzy uncertainties

    NASA Astrophysics Data System (ADS)

    Lü, Hui; Shangguan, Wen-Bin; Yu, Dejie

    2017-09-01

    Automotive brake systems are always subjected to various types of uncertainties and two types of random-fuzzy uncertainties may exist in the brakes. In this paper, a unified approach is proposed for squeal instability analysis of disc brakes with two types of random-fuzzy uncertainties. In the proposed approach, two uncertainty analysis models with mixed variables are introduced to model the random-fuzzy uncertainties. The first one is the random and fuzzy model, in which random variables and fuzzy variables exist simultaneously and independently. The second one is the fuzzy random model, in which uncertain parameters are all treated as random variables while their distribution parameters are expressed as fuzzy numbers. Firstly, the fuzziness is discretized by using α-cut technique and the two uncertainty analysis models are simplified into random-interval models. Afterwards, by temporarily neglecting interval uncertainties, the random-interval models are degraded into random models, in which the expectations, variances, reliability indexes and reliability probabilities of system stability functions are calculated. And then, by reconsidering the interval uncertainties, the bounds of the expectations, variances, reliability indexes and reliability probabilities are computed based on Taylor series expansion. Finally, by recomposing the analysis results at each α-cut level, the fuzzy reliability indexes and probabilities can be obtained, by which the brake squeal instability can be evaluated. The proposed approach gives a general framework to deal with both types of random-fuzzy uncertainties that may exist in the brakes and its effectiveness is demonstrated by numerical examples. It will be a valuable supplement to the systematic study of brake squeal considering uncertainty.

  8. Rethinking Black Hole Accretion Discs

    NASA Astrophysics Data System (ADS)

    Salvesen, Greg

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

  9. Spatial and structural dependence of mechanical properties of porcine intervertebral disc.

    PubMed

    Causa, F; Manto, L; Borzacchiello, A; De Santis, R; Netti, P A; Ambrosio, L; Nicolais, L

    2002-12-01

    Structure-function relationship of natural tissues is crucial to design a device mimicking the structures present in human body. For this purpose, to provide guidelines to design an intervertebral disc (IVD) substitute, in this study the influence of the spatial location and structural components on the mechanical properties of porcine IVD was investigated. Local compressive stiffness (LCS) was measured on the overall disc, also constrained between the two adjacent vertebrae: the dependence on the lumbar position was evaluated. The compliance values in the anterior position (A) were higher than both in the central posterior (CP) and in the lateral-posterior (RP, LP) locations. The values of Young's Modulus (74.67+/-6.03 MPa) and compression break load (1.36x10(4)+/-0.09x10(4)N) of the disc were also evaluated by distributed compression test. The NP rheological behavior was typical of weak-gels, with elastic modulus G' always higher than viscous modulus G" all over the frequency range investigated (G' and G" respectively equal to 320 and 85 Pa at 1 Hz) and with the moduli trends were almost parallel to each other.

  10. Myc-dependent genome instability and lifespan in Drosophila.

    PubMed

    Greer, Christina; Lee, Moonsook; Westerhof, Maaike; Milholland, Brandon; Spokony, Rebecca; Vijg, Jan; Secombe, Julie

    2013-01-01

    The Myc family of transcription factors are key regulators of cell growth and proliferation that are dysregulated in a large number of human cancers. When overexpressed, Myc family proteins also cause genomic instability, a hallmark of both transformed and aging cells. Using an in vivo lacZ mutation reporter, we show that overexpression of Myc in Drosophila increases the frequency of large genome rearrangements associated with erroneous repair of DNA double-strand breaks (DSBs). In addition, we find that overexpression of Myc shortens adult lifespan and, conversely, that Myc haploinsufficiency reduces mutation load and extends lifespan. Our data provide the first evidence that Myc may act as a pro-aging factor, possibly through its ability to greatly increase genome instability.

  11. The TP53 dependence of radiation-induced chromosome instability in human lymphoblastoid cells

    NASA Technical Reports Server (NTRS)

    Schwartz, Jeffrey L.; Jordan, Robert; Evans, Helen H.; Lenarczyk, Marek; Liber, Howard

    2003-01-01

    The dose and TP53 dependence for the induction of chromosome instability were examined in cells of three human lymphoblastoid cell lines derived from WIL2 cells: TK6, a TP53-normal cell line, NH32, a TP53-knockout created from TK6, and WTK1, a WIL2-derived cell line that spontaneously developed a TP53 mutation. Cells of each cell line were exposed to (137)Cs gamma rays, and then surviving clones were isolated and expanded in culture for approximately 35 generations before the frequency and characteristics of the instability were analyzed. The presence of dicentric chromosomes, formed by end-to-end fusions, served as a marker of chromosomal instability. Unexposed TK6 cells had low levels of chromosomal instability (0.002 +/- 0.001 dicentrics/cell). Exposure of TK6 cells to doses as low as 5 cGy gamma rays increased chromosome instability levels nearly 10-fold to 0.019 +/- 0.008 dicentrics/cell. There was no further increase in instability levels beyond 5 cGy. In contrast to TK6 cells, unexposed cultures of WTK1 and NH32 cells had much higher levels of chromosome instability of 0.034 +/- 0.007 and 0.041 +/- 0.009, respectively, but showed little if any effect of radiation on levels of chromosome instability. The results suggest that radiation exposure alters the normal TP53-dependent cell cycle checkpoint controls that recognize alterations in telomere structure and activate apoptosis.

  12. The TP53 dependence of radiation-induced chromosome instability in human lymphoblastoid cells

    NASA Technical Reports Server (NTRS)

    Schwartz, Jeffrey L.; Jordan, Robert; Evans, Helen H.; Lenarczyk, Marek; Liber, Howard

    2003-01-01

    The dose and TP53 dependence for the induction of chromosome instability were examined in cells of three human lymphoblastoid cell lines derived from WIL2 cells: TK6, a TP53-normal cell line, NH32, a TP53-knockout created from TK6, and WTK1, a WIL2-derived cell line that spontaneously developed a TP53 mutation. Cells of each cell line were exposed to (137)Cs gamma rays, and then surviving clones were isolated and expanded in culture for approximately 35 generations before the frequency and characteristics of the instability were analyzed. The presence of dicentric chromosomes, formed by end-to-end fusions, served as a marker of chromosomal instability. Unexposed TK6 cells had low levels of chromosomal instability (0.002 +/- 0.001 dicentrics/cell). Exposure of TK6 cells to doses as low as 5 cGy gamma rays increased chromosome instability levels nearly 10-fold to 0.019 +/- 0.008 dicentrics/cell. There was no further increase in instability levels beyond 5 cGy. In contrast to TK6 cells, unexposed cultures of WTK1 and NH32 cells had much higher levels of chromosome instability of 0.034 +/- 0.007 and 0.041 +/- 0.009, respectively, but showed little if any effect of radiation on levels of chromosome instability. The results suggest that radiation exposure alters the normal TP53-dependent cell cycle checkpoint controls that recognize alterations in telomere structure and activate apoptosis.

  13. Godzilla-dependent transcytosis promotes Wingless signalling in Drosophila wing imaginal discs

    PubMed Central

    Yamazaki, Yasuo; Palmer, Lucy; Alexandre, Cyrille; Kakugawa, Satoshi; Beckett, Karen; Gaugue, Isabelle; Palmer, Ruth H.; Vincent, Jean-Paul

    2016-01-01

    The apical and basolateral membranes of epithelia are insulated from each other, preventing the transfer of extracellular proteins from one side to the other1. Thus, a signalling protein produced apically is not expected to reach basolateral receptors. Evidence suggests that Wingless, the main Drosophila Wnt is secreted apically in the embryonic epidermis2, 3. However, in the wing imaginal disc epithelium, Wingless is mostly seen on the basolateral membrane where it spreads from secreting to receiving cells 4, 5. Here we examine the apico-basal movement of Wingless in Wingless-producing cells of wing imaginal discs. We find that it is presented first on the apical surface before making its way to the basolateral surface, where it is released and allowed to interact with signalling receptors. We show that Wingless transcytosis involves Dynamin-dependent endocytosis from the apical surface. Subsequent trafficking from early apical endosomes to the basolateral surface requires Godzilla, a member of the RNF family of membrane-anchored E3 ubiquitin ligases. Without such transport, Wingless signalling is strongly reduced in this tissue. PMID:26974662

  14. On the parameter dependence of the whistler anisotropy instability

    NASA Astrophysics Data System (ADS)

    An, Xin; Yue, Chao; Bortnik, Jacob; Decyk, Viktor; Li, Wen; Thorne, Richard M.

    2017-02-01

    The evolution of the whistler anisotropy instability relevant to whistler-mode chorus waves in the Earth's inner magnetosphere is studied using kinetic simulations and is compared with satellite observations. The electron distribution is constrained by the whistler anisotropy instability to a marginal stability state and presents an upper bound of electron anisotropy, which agrees with satellite observations. The electron beta β∥e separates whistler waves into two groups: (i) quasi-parallel whistler waves for β∥e≳0.02 and (ii) oblique whistler waves close to the resonance cone for β∥e≲0.02. Landau damping is important in the saturation and relaxation stage of the oblique whistler wave growth. The saturated magnetic field energy of whistler waves roughly scales with the electron beta β∥e2, shown in both simulations and satellite observations. These results suggest the critical role of electron beta β∥e in determining the whistler wave properties in the inner magnetosphere.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. p53-Dependent suppression of genome instability in germ cells.

    PubMed

    Otozai, Shinji; Ishikawa-Fujiwara, Tomoko; Oda, Shoji; Kamei, Yasuhiro; Ryo, Haruko; Sato, Ayuko; Nomura, Taisei; Mitani, Hiroshi; Tsujimura, Tohru; Inohara, Hidenori; Todo, Takeshi

    2014-02-01

    Radiation increases mutation frequencies at tandem repeat loci. Germline mutations in γ-ray-irradiated medaka fish (Oryzias latipes) were studied, focusing on the microsatellite loci. Mismatch-repair genes suppress microsatellite mutation by directly removing altered sequences at the nucleotide level, whereas the p53 gene suppresses genetic alterations by eliminating damaged cells. The contribution of these two defense mechanisms to radiation-induced microsatellite instability was addressed. The spontaneous mutation frequency was significantly higher in msh2(-/-) males than in wild-type fish, whereas there was no difference in the frequency of radiation-induced mutations between msh2(-/-) and wild-type fish. By contrast, irradiated p53(-/-) fish exhibited markedly increased mutation frequencies, whereas their spontaneous mutation frequency was the same as that of wild-type fish. In the spermatogonia of the testis, radiation induced a high level of apoptosis both in wild-type and msh2(-/-) fish, but negligible levels in p53(-/-) fish. The results demonstrate that the msh2 and p53 genes protect genome integrity against spontaneous and radiation-induced mutation by two different pathways: direct removal of mismatches and elimination of damaged cells.

  17. Proto-planetary disc evolution and dispersal

    NASA Astrophysics Data System (ADS)

    Rosotti, Giovanni Pietro

    2015-05-01

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

  18. Mass dependence of instabilities of an oscillator with multiplicative and additive noise.

    PubMed

    Gitterman, Moshe; Kessler, David A

    2013-02-01

    We study the instabilities of a harmonic oscillator subject to additive and dichotomous multiplicative noise, focusing on the dependence of the instability threshold on the mass. For multiplicative noise in the damping, the energy instability threshold is crossed as the mass is decreased, as long as the smaller damping is in fact negative. For multiplicative noise in the stiffness, the situation is more complicated and in fact the energy transition is reentrant for intermediate noise strength and damping. For multiplicative noise in the mass, the results depend on the implementation of the noise. One can take the velocity or the momentum to be conserved as the mass is changed. In these cases increasing the mass destabilizes the system. Alternatively, if the change in mass is caused by the accretion and loss of particles to the Brownian particle, these processes are asymmetric with momentum conserved upon accretion and velocity upon loss. In this case, there is no instability, as opposed to the other two implementations. We also present the mass dependence of the instability threshold for the first moment. Finally, we study the distribution of the energy, finding a power-law cutoff at a value that increases with time.

  19. Instabilities of conducting fluid layers in weak time-dependent magnetic fields

    NASA Astrophysics Data System (ADS)

    Cortés-Domínguez, I.; Burguete, J.

    2017-07-01

    We present the experimental analysis of the instabilities generated on a large drop of liquid metal by a time-dependent magnetic field. The study is done exploring the range of tiny values of the control parameter (the ratio between the Lorentz forces and inertia) avoiding nonlinear effects. Two different instabilities break the symmetries generating spatial patterns that appear without a threshold for some specific frequencies (up to the experimental precision) and have been observed for parameter values two orders of magnitude lower than in previously published experiments [J. Fluid Mech. 239, 383 (1992), 10.1017/S0022112092004452]. One of the instabilities corresponds to a boundary condition oscillation that generates surface waves and breaks the azimuthal symmetry. The other corresponds to a parametric forcing through a modulation of the Lorentz force. The competition between these two mechanisms produces time-dependent patterns near codimension-2 points.

  20. Concentration-dependent diffusion instability in reactive miscible fluids

    NASA Astrophysics Data System (ADS)

    Bratsun, Dmitry; Kostarev, Konstantin; Mizev, Aleksey; Mosheva, Elena

    2015-07-01

    We report on chemoconvective pattern formation phenomena observed in a two-layer system of miscible fluids filling a vertical Hele-Shaw cell. We show both experimentally and theoretically that the concentration-dependent diffusion coupled with frontal acid-base neutralization can give rise to the formation of a local unstable zone low in density, resulting in a perfectly regular cell-type convective pattern. The described effect gives an example of yet another powerful mechanism which allows the reaction-diffusion processes to govern the flow of reacting fluids under gravity conditions.

  1. Dependence of turbulent Rayleigh-Taylor instability on initial perturbations.

    PubMed

    Dimonte, Guy

    2004-05-01

    The dependency of the self-similar Rayleigh-Taylor bubble acceleration constant alpha(b)(identical with [(amplitude)/2] x (displacement) x (Atwood number)) on the initial perturbation amplitude h(0k) is described with a model in which the exponential growth of a small amplitude packet of modes makes a continuous nonlinear transition to its "terminal" bubble velocity proportional, variant Fr[equal to(Froude number)(1/2)]. Then, by applying self-similarity (diameter proportional, variant amplitude), alpha(b) is found to increase proportional to Fr and logarithmically with h(0k). The model has two free parameters that are determined from experiments and simulations. The augmentation of long wavelength perturbations by mode coupling is also evaluated. This is found to decrease the sensitivity of alpha(b) on the initial perturbations when they are smaller than the saturation amplitude of the most unstable modes. These results show that alpha(b) can vary by a factor of 2-3 with initial conditions in reasonable agreement with experiments and simulations.

  2. Convective instability in a two-layer system of reacting fluids with concentration-dependent diffusion

    NASA Astrophysics Data System (ADS)

    Aitova, E. V.; Bratsun, D. A.; Kostarev, K. G.; Mizev, A. I.; Mosheva, E. A.

    2016-12-01

    The development of convective instability in a two-layer system of miscible fluids placed in a narrow vertical gap has been studied theoretically and experimentally. The upper and lower layers are formed with aqueous solutions of acid and base, respectively. When the layers are brought into contact, the frontal neutralization reaction begins. We have found experimentally a new type of convective instability, which is characterized by the spatial localization and the periodicity of the structure observed for the first time in the miscible systems. We have tested a number of different acid-base systems and have found a similar patterning there. In our opinion, it may indicate that the discovered effect is of a general nature and should be taken into account in reaction-diffusion-convection problems as another tool with which the reaction can govern the movement of the reacting fluids. We have shown that, at least in one case (aqueous solutions of nitric acid and sodium hydroxide), a new type of instability called as the concentration-dependent diffusion convection is responsible for the onset of the fluid flow. It arises when the diffusion coefficients of species are different and depend on their concentrations. This type of instability can be attributed to a variety of double-diffusion convection. A mathematical model of the new phenomenon has been developed using the system of reaction-diffusion-convection equations written in the Hele-Shaw approximation. It is shown that the instability can be reproduced in the numerical experiment if only one takes into account the concentration dependence of the diffusion coefficients of the reagents. The dynamics of the base state, its linear stability and nonlinear development of the instability are presented. It is also shown that by varying the concentration of acid in the upper layer one can achieve the occurrence of chemo-convective solitary cell in the bulk of an almost immobile fluid. Good agreement between the

  3. MyD88-dependent Toll-like receptor 4 signal pathway in intervertebral disc degeneration

    PubMed Central

    Qin, Chuqiang; Zhang, Bo; Zhang, Liang; Zhang, Zhi; Wang, Le; Tang, Long; Li, Shuangqing; Yang, Yixi; Yang, Fuguo; Zhang, Ping; Yang, Bo

    2016-01-01

    Lower back pain (LBP) is a common and remitting problem. One of the primary causes of LBP is thought to be degeneration of the intervertebral disc (IVD). The aim of the present study was to investigate the role of the myeloid differentiation primary-response protein 88 (MyD88)-dependent Toll-like receptor 4 (TLR4) signal pathway in the mechanism of IVD degeneration. IVD nucleus pulposus cells isolated and cultured from the lumbar vertebrae of Wistar rats were stimulated by various doses of lipopolysaccharide (LPS; 0.1, 1, 10 and 100 µg/ml) to simulate IVD degeneration. Cells were rinsed and cultured in serum-free Dulbecco's modified Eagle's medium/F12. Reverse transcription-quantitative polymerase chain reaction was used to determine the levels of TLR4, MyD88, tumor necrosis factor α (TNFα), and interleukin-1β (IL-1β) mRNA expression after 1, 3, 6, 9 and 12 h of incubation. Additionally, western blot and enzyme-linked immunosorbent assay analyses were used to determine the levels of TLR4, MyD88, TNFα, and IL-1β protein expression after 24, 48 and 72 h of incubation. The levels of TLR4, MyD88, TNFα and IL-1β mRNA all increased in the cells stimulated by 10 µg/ml LPS at 3, 6 and 9 h (all P<0.001). Furthermore, the levels of TLR4, MyD88, TNFα and IL-1β protein all increased at 24, 48 and 72 h (all P<0.001). Additionally, the mRNA and protein levels of TLR4, MyD88, TNFα and IL-1β increased significantly in the cells stimulated by 1, 10 and 100 µg/ml LPS compared with the control group, and reached a peak in the 10 µg/ml LPS group (all P<0.001). These results suggest that the MyD88-dependent TLR4 signal pathway is a target pathway in IVD degeneration. This pathway is time phase- and dose-dependent, and when activated can lead to the release of inflammatory factors that participate in IVD degeneration. PMID:27446251

  4. Time-dependent modes associated with finite time instabilities in unstable fluid flows

    NASA Astrophysics Data System (ADS)

    Babaee, Hessam; Sapsis, Themistoklis

    2015-11-01

    We apply a recently developed variational formulation for the determination of a finite-dimensional, time-dependent, orthonormal basis that captures the directions associated with finite-time instabilities. We demonstrate the capability of the method for two problems: the Orr-Sommerfeld/Squire operator and the vertical jet in crossflow. In the first problem we demonstrate that the time-dependent subspace captures the strongly transient non-normal energy growth (in the short time regime), while for longer times the modes capture the expected asymptotic behavior of the dynamics. We also consider the vertical jet in crossflow at the jet Reynolds number of Rej = 900 . We demonstrate that the subspace instantaneously captures the most unstable directions of the time-dependent flow. We explore the connection between the shear flow, non-normal growth and persistent instabilities. Supported by ARO Award # 66710-EG-YIP.

  5. The Effect of Discectomy and the Dependence on Degeneration of Human Intervertebral Disc Strain in Axial Compression

    PubMed Central

    O’Connell, Grace D.; Malhotra, Neil R.; Vresilovic, Edward J; Elliott, Dawn M.

    2011-01-01

    Study Design Biomechanics of human intervertebral discs before and after nucleotomy. Objective To noninvasively quantify the effect of nucleotomy on internal strains under axial compression in flexion, neutral, and extension positions, and to determine whether the change in strains depended on degeneration. Summary of Background Data Herniation and discectomy may accelerate the progression of disc degeneration. Removal of NP tissue has resulted in altered disc mechanics in vitro, including in a decrease in internal pressure and an increase in the deformations at physiologically relevant strains. We recently presented a technique to quantify internal disc strains using magnetic resonance imaging. Methods Degeneration was quantitatively assessed by the T1ρ relaxation in the nucleus pulposus (NP). Samples were prepared from human levels L3-L4 and/or L4-L5. A 1000N compressive load was applied while in the MR scanner. Nucleotomy was performed by removing 2g of NP through the posterior-lateral AF. The discs were rehydrated, reimaged and retested. The analyzed parameters include axial deformation, AF radial bulge and strains. Results The axial deformation was more compressive following nucleotomy. In the neutral position, the axial deformation following nucleotomy correlated with degeneration (as quantified by T1ρ in the NP), with minimal alteration in nondegenerated discs. Nucleotomy altered the radial displacements and strains in the neutral position, such that the inner AF radial bulge decreased and the radial strains were more tensile in the lateral AF and less tensile in the posterior AF. In the bending loading positions the radial strains were not affected by nucleotomy. Conclusions Nucleotomy alters the internal radial and axial AF strains in the neutral position, which may leave the AF vulnerable to damage and microfractures. In bending, the effects of nucleotomy were minimal; likely due to more of the applied load being directed over the AF. Some of the

  6. Composition and substrate-dependent strength of the silken attachment discs in spiders

    PubMed Central

    Grawe, Ingo; Wolff, Jonas O.; Gorb, Stanislav N.

    2014-01-01

    Araneomorph spiders have evolved different silks with dissimilar material properties, serving different purposes. The two-compound pyriform secretion is used to glue silk threads to substrates or to other threads. It is applied in distinct patterns, called attachment discs. Although ubiquitously found in spider silk applications and hypothesized to be strong and versatile at low material consumption, the performance of attachment discs on different substrates remains unknown. Here, we analyse the detachment forces and fracture mechanics of the attachment discs spun by five different species on three different substrates, by pulling on the upstream part of the attached thread. Results show that although the adhesion of the pyriform glue is heavily affected by the substrate, even on Teflon it is frequently strong enough to hold the spider's weight. As plant surfaces are often difficult to wet, they are hypothesized to be the major driving force for evolution of the pyriform secretion. PMID:25030386

  7. Radiation magnetohydrodynamics in global simulations of protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Flock, M.; Fromang, S.; González, M.; Commerçon, B.

    2013-12-01

    Aims: Our aim is to study the thermal and dynamical evolution of protoplanetary discs in global simulations, including the physics of radiation transfer and magneto-hydrodynamic turbulence caused by the magneto-rotational instability. Methods: We have developed a radiative transfer method based on the flux-limited diffusion approximation that includes frequency dependent irradiation by the central star. This hybrid scheme is implemented in the PLUTO code. The focus of our implementation is on the performance of the radiative transfer method. Using an optimized Jacobi preconditioned BiCGSTAB solver, the radiative module is three times faster than the magneto-hydrodynamic step for the disc set-up we consider. We obtain weak scaling efficiencies of 70% up to 1024 cores. Results: We present the first global 3D radiation magneto-hydrodynamic simulations of a stratified protoplanetary disc. The disc model parameters were chosen to approximate those of the system AS 209 in the star-forming region Ophiuchus. Starting the simulation from a disc in radiative and hydrostatic equilibrium, the magneto-rotational instability quickly causes magneto-hydrodynamic turbulence and heating in the disc. We find that the turbulent properties are similar to that of recent locally isothermal global simulations of protoplanetary discs. For example, the rate of angular momentum transport α is a few times 10-3. For the disc parameters we use, turbulent dissipation heats the disc midplane and raises the temperature by about 15% compared to passive disc models. The vertical temperature profile shows no temperature peak at the midplane as in classical viscous disc models. A roughly flat vertical temperature profile establishes in the optically thick region of the disc close to the midplane. We reproduce the vertical temperature profile with viscous disc models for which the stress tensor vertical profile is flat in the bulk of the disc and vanishes in the disc corona. Conclusions: The present

  8. DEPENDENCE OF THE SATURATION LEVEL OF MAGNETOROTATIONAL INSTABILITY ON GAS PRESSURE AND MAGNETIC PRANDTL NUMBER

    SciTech Connect

    Minoshima, Takashi; Hirose, Shigenobu; Sano, Takayoshi

    2015-07-20

    A large set of numerical simulations of MHD turbulence induced by the magnetorotational instability is presented. Revisiting the previous survey conducted by Sano et al., we investigate the gas pressure dependence of the saturation level. In ideal MHD simulations, the gas pressure dependence is found to be very sensitive to the choice of numerical scheme. This is because the numerical magnetic Prandtl number varies according to the scheme as well as the pressure, which considerably affects the results. The saturation level is more sensitive to the numerical magnetic Prandtl number than the pressure. In MHD simulations with explicit viscosity and resistivity, the saturation level increases with the physical magnetic Prandtl number, and it is almost independent of the gas pressure when the magnetic Prandtl number is constant. This is indicative of the incompressible turbulence saturated by the secondary tearing instability.

  9. Local and global dynamics of warped astrophysical discs

    NASA Astrophysics Data System (ADS)

    Ogilvie, Gordon I.; Latter, Henrik N.

    2013-08-01

    Astrophysical discs are warped whenever a misalignment is present in the system, or when a flat disc is made unstable by external forces. The evolution of the shape and mass distribution of a warped disc is driven not only by external influences but also by an internal torque, which transports angular momentum through the disc. This torque depends on internal flows driven by the oscillating pressure gradient associated with the warp, and on physical processes operating on smaller scales, which may include instability and turbulence. We introduce a local model for the detailed study of warped discs. Starting from the shearing sheet of Goldreich and Lynden-Bell, we impose the oscillating geometry of the orbital plane by means of a coordinate transformation. This warped shearing sheet (or box) is suitable for analytical and computational treatments of fluid dynamics, magnetohydrodynamics, etc., and it can be used to compute the internal torque that drives the large-scale evolution of the disc. The simplest hydrodynamic states in the local model are horizontally uniform laminar flows that oscillate at the orbital frequency. These correspond to the non-linear solutions for warped discs found in previous work by Ogilvie, and we present an alternative derivation and generalization of that theory. In a companion paper, we show that these laminar flows are often linearly unstable, especially if the disc is nearly Keplerian and of low viscosity. The local model can be used in future work to determine the non-linear outcome of the hydrodynamic instability of warped discs, and its interaction with others such as the magnetorotational instability.

  10. Highly symmetric interfacial coherent structures in Rayleigh Taylor instability with time-dependent acceleration

    NASA Astrophysics Data System (ADS)

    Bhowmick, Aklant K.; Abarzhi, Snezhana

    2016-11-01

    Rayleigh Taylor instability in a power-law time dependent acceleration field is investigated theoretically for a flow with the symmetry group p6mm (hexagon) in the plane normal to acceleration. In the nonlinear regime, regular asymptotic solutions form a one-parameter family. The physically significant solution is identified with the one having the fastest growth and being stable (bubble tip velocity). Two distinct regimes are identified depending on the acceleration exponent. Particularly, the RM-type regime, where the dynamics is identical to conventional RM instability and is dominated by initial conditions, and the RT-type regime where the dynamics is dominated by the acceleration term. For the latter, the time dependence has profound effects on the dynamics. In the RT non-linear regime, the time dependence has no consequence on the morphology of the bubbles; the growth rate (bubble tip velocity) evolves as power law with the exponent set by the acceleration. The solutions for a one-parameter family, and are convergent with exponential decay of Fourier amplitudes. The solutions are stable at maximum tip velocity, whereas flat bubbles are unstable, and the growth/decay of perturbations is no longer purely exponential and depends on the acceleration exponent. The work is supported by the US National Science Foundation.

  11. Highly symmetric interfacial structures in Rayleigh Taylor instability with time-dependent acceleration

    NASA Astrophysics Data System (ADS)

    Bhowmick, Aklant K.; Abarzhi, Snezhana

    2016-10-01

    Rayleigh Taylor instability in a power-law time dependent acceleration field is investigated for a flow with the symmetry group p6mm (hexagonal) in the plane normal to acceleration. The Regular asymptotic solutions form a one-parameter family and the physically significant solution is identified with the one having the fastest growth and being stable (bubble tip velocity). Two distinct regimes are identified dependent on the acceleration exponent, the RM-type regime, where the dynamics is identical to conventional RM instability and is dominated by initial conditions, and the RT-type regime where the dynamics is dominated by the acceleration term. For the latter, the time dependence has profound effects on the dynamics. In the RT non-linear regime, the time dependence has no consequence on the morphology of the bubbles but the growth rate (bubble tip velocity) evolves as power law with the exponent set by the acceleration. The solutions for a one-parameter family, and are convergent with exponential decay of Fourier amplitudes close to the physical solution. The solutions are stable at maximum tip velocity and flat bubbles are unstable, and the growth/decay of perturbations is no longer purely exponential and depends on the acceleration exponent. The work is supported by the US National Science Foundation.

  12. Validation and application of an intervertebral disc finite element model utilizing independently constructed tissue-level constitutive formulations that are nonlinear, anisotropic, and time-dependent.

    PubMed

    Jacobs, Nathan T; Cortes, Daniel H; Peloquin, John M; Vresilovic, Edward J; Elliott, Dawn M

    2014-08-22

    Finite element (FE) models are advantageous in the study of intervertebral disc mechanics as the stress-strain distributions can be determined throughout the tissue and the applied loading and material properties can be controlled and modified. However, the complicated nature of the disc presents a challenge in developing an accurate and predictive disc model, which has led to limitations in FE geometry, material constitutive models and properties, and model validation. The objective of this study was to develop a new FE model of the intervertebral disc, to validate the model's nonlinear and time-dependent responses without tuning or calibration, and to evaluate the effect of changes in nucleus pulposus (NP), cartilaginous endplate (CEP), and annulus fibrosus (AF) material properties on the disc mechanical response. The new FE disc model utilized an analytically-based geometry. The model was created from the mean shape of human L4/L5 discs, measured from high-resolution 3D MR images and averaged using signed distance functions. Structural hyperelastic constitutive models were used in conjunction with biphasic-swelling theory to obtain material properties from recent tissue tests in confined compression and uniaxial tension. The FE disc model predictions fit within the experimental range (mean ± 95% confidence interval) of the disc's nonlinear response for compressive slow loading ramp, creep, and stress-relaxation simulations. Changes in NP and CEP properties affected the neutral-zone displacement but had little effect on the final stiffness during slow-ramp compression loading. These results highlight the need to validate FE models using the disc's full nonlinear response in multiple loading scenarios.

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

    NASA Astrophysics Data System (ADS)

    Margalit, Ben; Metzger, Brian D.

    2016-09-01

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

  14. Methods to detect replication-dependent and replication-independent DNA structure-induced genetic instability

    PubMed Central

    Wang, Guliang; Gaddis, Sally; Vasquez, Karen M.

    2013-01-01

    DNA can adopt a variety of alternative secondary (i.e., non-B DNA) conformations that play important roles in cellular metabolism, including genetic instability, disease etiology, and evolution. While we still have much to learn, research in this field has expanded dramatically in the past decade. We have summarized in our previous Methods review (Wang et al., Methods, 2009) some commonly used techniques to determine non-B DNA structural conformations and non-B DNA-induced genetic instability in prokaryotes and eukaryotes. Since that time, we and others have further characterized mechanisms involved in DNA structure-induced mutagenesis and have proposed both replication-dependent and replication-independent models. Thus, in this review, we highlight some current methodologies to identify DNA replication-related and replication-independent mutations occurring at non-B DNA regions to allow for a better understanding of the mechanisms underlying DNA structure-induced genetic instability. We also describe a new web-based search engine to identify potential intramolecular triplex (H-DNA) and left-handed Z-DNA-forming motifs in entire genomes or at selected sequences of interest. PMID:23954565

  15. 1990 Volvo Award in experimental studies. The dependence of intervertebral disc mechanical properties on physiologic conditions.

    PubMed

    Keller, T S; Holm, S H; Hansson, T H; Spengler, D M

    1990-08-01

    In vivo creep-recovery and disc pressure measurements were performed on the lumbar spine of immature and mature swine. The creep-recovery measurements were performed using a custom materials testing apparatus designed to apply static or dynamic loads to the spine of anesthetized animals. A series of three separate experiments were performed to assess the effects of: (I) animal death, (II) graded injury to the disc anulus, and (III) respiratory mechanics on the biomechanical response of the porcine L1-L3 vertebral unit (VU). In Experiments I and II, creep rate, modulus, and viscosity parameters were computed using a three-parameter solid rheological analysis of the displacement-time response recorded during the application of a 300-N load. In Experiment III, the effects of respiratory volume and frequency changes on disc pressure were assessed in the unloaded, statically loaded, and immobilized porcine VU. Our results indicated that the adult VU tended to be stiffer, deform or creep more slowly, and had a significantly higher viscosity than the VU of immature pigs. The results of Experiment I demonstrated that the biomechanical response for the VU was significantly altered by the death of the animal; the VU of the living animal (adolescent or mature) was more compliant and deformed at a faster rate than the VU of the same animal after death. Disc injury produced changes in stiffness, viscosity, and creep rate analogous to that of aging, and on the basis of the graded injuries created in this study, it appears that a small defect in the annulus is just as deleterious as removing a large section of anular material. The results of Experiment III indicated that respiration plays an important role in the normal, in vivo mechanical and nutritional behavior of the porcine VU. Altogether, these results demonstrate that, in the absence of normal physiologic conditions, one may not be able to reliably predict the mechanical response of the lumbar spine, and suggest that

  16. Efficiency of thermal relaxation by radiative processes in protoplanetary discs: constraints on hydrodynamic turbulence

    NASA Astrophysics Data System (ADS)

    Malygin, M. G.; Klahr, H.; Semenov, D.; Henning, Th.; Dullemond, C. P.

    2017-09-01

    Context. Hydrodynamic, non-magnetic instabilities can provide turbulent stress in the regions of protoplanetary discs, where the magneto-rotational instability can not develop. The induced motions influence the grain growth, from which formation of planetesimals begins. Thermal relaxation of the gas constrains origins of the identified hydrodynamic sources of turbulence in discs. Aims: We aim to estimate the radiative relaxation timescale of temperature perturbations in protoplanetary discs. We study the dependence of the thermal relaxation on the perturbation wavelength, the location within the disc, the disc mass, and the dust-to-gas mass ratio. We then apply thermal relaxation criteria to localise modes of the convective overstability, the vertical shear instability, and the zombie vortex instability. Methods: For a given temperature perturbation, we estimated two timescales: the radiative diffusion timescale tthick and the optically thin emission timescale tthin. The longest of these timescales governs the relaxation: trelax = max (tthick, tthin). We additionally accounted for the collisional coupling to the emitting species. Our calculations employed the latest tabulated dust and gas mean opacities. Results: The relaxation criterion defines the bulk of a typical T Tauri disc as unstable to the development of linear hydrodynamic instabilities. The midplane is unstable to the convective overstability from at most 2au and up to 40au, as well as beyond 140au. The vertical shear instability can develop between 15au and 180au. The successive generation of (zombie) vortices from a seeded noise can work within the inner 0.8au. Conclusions: A map of relaxation timescale constrains the origins of the identified hydrodynamic turbulence-driving mechanisms in protoplanetary discs. Dynamic disc modelling with the evolution of dust and gas opacities is required to clearly localise the hydrodynamic turbulence, and especially its non-linear phase.

  17. Force-free state in a superconducting single crystal and angle-dependent vortex helical instability

    NASA Astrophysics Data System (ADS)

    del Valle, J.; Gomez, A.; Gonzalez, E. M.; Manas-Valero, S.; Coronado, E.; Vicent, J. L.

    2017-06-01

    Superconducting 2 H -NbS e2 single crystals show intrinsic low pinning values. Therefore, they are ideal materials with which to explore fundamental properties of vortices. (V , I ) characteristics are the experimental data we have used to investigate the dissipation mechanisms in a rectangular-shaped 2 H -NbS e2 single crystal. Particularly, we have studied dissipation behavior with magnetic fields applied in the plane of the crystal and parallel to the injected currents, i.e., in the force-free state where the vortex helical instability governs the vortex dynamics. In this regime, the data follow the elliptic critical state model and the voltage dissipation shows an exponential dependence, V ∝eα (I -IC ∥ ) , IC ∥ being the critical current in the force-free configuration and α a linear temperature-dependent parameter. Moreover, this exponential dependence can be observed for in-plane applied magnetic fields up to 40° off the current direction, which implies that the vortex helical instability plays a role in dissipation even out of the force-free configuration.

  18. Self-similar slip instability on interfaces with rate- and state-dependent friction

    NASA Astrophysics Data System (ADS)

    Viesca, Robert C.

    2016-08-01

    We examine the development of a frictional instability, with diverging sliding rate, at the interface of elastic bodies in contact. Evolution of friction is determined by a slip rate and state dependence. Following Viesca (2016 Phys. Rev. E 93, 060202(R). (doi:10.1103/PhysRevE.93.060202)), we show through an appropriate change of variable, the existence of blow-up solutions that are fixed points of a dynamical system. The solutions show self-similarity of the simple variety: separable dependence of time and space. For an interface with uniform frictional properties, there is a single-problem parameter. We examine the linear stability of these fixed points, as this problem parameter is varied. Specifically, we consider two archetypical elastic settings of the slip surface, in which interactions between points on the surface are either local or non-local. We show that, independent of the nature of elastic interactions, the fixed-points lose stability in the same matter as the parameter is increased towards a limit value: an apparently infinite sequence of Hopf bifurcations. However, for any value of the parameter, the nonlinear development of the instability is attraction, if not asymptotic convergence, towards these fixed points, owing to the existence of stable eigenmodes. For comparison, we perform numerical solutions of the original evolution equations and find precise agreement with the results of the analysis.

  19. Self-similar slip instability on interfaces with rate- and state-dependent friction

    PubMed Central

    2016-01-01

    We examine the development of a frictional instability, with diverging sliding rate, at the interface of elastic bodies in contact. Evolution of friction is determined by a slip rate and state dependence. Following Viesca (2016 Phys. Rev. E 93, 060202(R). (doi:10.1103/PhysRevE.93.060202)), we show through an appropriate change of variable, the existence of blow-up solutions that are fixed points of a dynamical system. The solutions show self-similarity of the simple variety: separable dependence of time and space. For an interface with uniform frictional properties, there is a single-problem parameter. We examine the linear stability of these fixed points, as this problem parameter is varied. Specifically, we consider two archetypical elastic settings of the slip surface, in which interactions between points on the surface are either local or non-local. We show that, independent of the nature of elastic interactions, the fixed-points lose stability in the same matter as the parameter is increased towards a limit value: an apparently infinite sequence of Hopf bifurcations. However, for any value of the parameter, the nonlinear development of the instability is attraction, if not asymptotic convergence, towards these fixed points, owing to the existence of stable eigenmodes. For comparison, we perform numerical solutions of the original evolution equations and find precise agreement with the results of the analysis. PMID:27616923

  20. Instability in the dense supernova neutrino gas with flavor-dependent angular distributions.

    PubMed

    Mirizzi, Alessandro; Serpico, Pasquale Dario

    2012-06-08

    The usual description of self-induced flavor conversions for neutrinos (ν's) in supernovae is based on the simplified assumption that all the ν's of the different species are emitted "half-isotropically" by a common neutrinosphere, in analogy to a blackbody emission. However, realistic supernova simulations show that ν angular distributions at decoupling are far from being half-isotropic and, above all, are flavor dependent. We show that flavor-dependent angular distributions may lead to crossing points in the angular spectra of different ν species (where F(ν(e))=F(ν(x)) and F(ν(e))=F(ν(x))) around which a new multiangle instability can develop. To characterize this effect, we carry out a linearized flavor stability analysis for different supernova neutrino angular distributions. We find that this instability can shift the onset of the flavor conversions toward low radii and produce a smearing of the splitting features found with trivial ν emission models. As a result the spectral differences among ν's of different flavors could be strongly reduced.

  1. Peeling-angle dependence of the stick-slip instability during adhesive tape peeling.

    PubMed

    Dalbe, Marie-Julie; Santucci, Stéphane; Vanel, Loïc; Cortet, Pierre-Philippe

    2014-12-28

    The influence of peeling angle on the dynamics observed during the stick-slip peeling of an adhesive tape has been investigated. This study relies on a new experimental setup for peeling at a constant driving velocity while keeping constant the peeling angle and peeled tape length. The thresholds of the instability are shown to be associated with a subcritical bifurcation and bistability of the system. The velocity onset of the instability is moreover revealed to strongly depend on the peeling angle. This could be the consequence of peeling angle dependance of either the fracture energy of the adhesive-substrate joint or the effective stiffness at play between the peeling front and the point at which the peeling is enforced. The shape of the peeling front velocity fluctuations is finally shown to progressively change from typical stick-slip relaxation oscillations to nearly sinusoidal oscillations as the peeling angle is increased. We suggest that this transition might be controlled by inertial effects possibly associated with the propagation of the peeling force fluctuations through elongation waves in the peeled tape.

  2. Generalized Rayleigh-Taylor instability in the presence of time-dependent equilibrium

    NASA Astrophysics Data System (ADS)

    Basu, B.

    1997-08-01

    Plasma instability under the combined influence of the gravity and an eastward electric field, commonly referred to as the generalized Rayleigh-Taylor instability, is considered for a time-dependent equilibrium situation. In the nighttime equatorial ionosphere the time-dependent equilibrium situation arises because of the vertically upward EB0 drift of the plasma in conjunction with the altitude-dependent recombination process and the collisional diffusion process. After determining the time-dependent equilibrium density and, in particular, the inverse density gradient scale length L-1, which determines the growth rate of the instability, the stability of small-amplitude perturbations is analyzed. The general solution of the problem, where the effects of all of the above-mentioned processes are included simultaneously, requires numerical analysis. In this paper the effects are studied in limiting situations for which useful analytic solutions can be obtained. The effect of diffusion on L-1 is studied by neglecting both the upward plasma drift and the altitude variation of the recombination frequency νR, and it is verified that the effect is negligible for typical values of the ionospheric parameters. The effects of the other two processes on L-1 are studied by neglecting diffusion. The effect of the altitude variation of νR on the linear growth of the perturbations is studied by adopting the so-called local approximation. It is found that the value of L-1 and hence the value of the growth rate are enhanced by the altitude variation of νR. The enhancements rapidly increase with time to large values at lower altitudes and to significant values at higher altitudes when compared with the values for the spatially uniform νR case. Consequently, the time evolution of the instability and, more importantly, the level of fluctuations at saturation will be significantly affected by the enhancements. The nonlocal aspect of the instability in

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  4. Hybrid rocket instability

    NASA Technical Reports Server (NTRS)

    Greiner, B.; Frederick, R. A., Jr.

    1993-01-01

    The paper provides a brief review of theoretical and experimental studies concerned with hybrid rocket instability. The instabilities discussed include atomization and mixing instabilities, chuffing instabilities, pressure coupled combustion instabilities, and vortex shedding. It is emphasized that the future use of hybrid motor systems as viable design alternatives will depend on a better understanding of hybrid instability.

  5. Structure of radiation-dominated gravitoturbulent quasar discs

    NASA Astrophysics Data System (ADS)

    Shadmehri, Mohsen; Khajenabi, Fazeleh; Dib, Sami

    2017-02-01

    Self-gravitating accretion discs in a gravitoturbulent state, including radiation and gas pressures, are studied using a set of new analytical solutions. While the Toomre parameter of the disc remains close to its critical value for the onset of gravitational instability, the dimensionless stress parameter is uniquely determined from the thermal energy reservoir of the disc and its cooling rate. Our solutions are applicable to the accretion discs with dynamically important radiation pressure such as that in the quasars discs. We show that physical quantities of a gravitoturbulent disc in the presence of radiation are significantly modified compared to solutions with only gas pressure. We show that the dimensionless stress parameter is an increasing function of the radial distance so that its steepness strongly depends on the accretion rate. In a disc without radiation its slope is 4.5; however, we show that in the presence of radiation, it varies between 2 and 4.5 depending on the accretion rate and the central mass. As for the surface density, we find a shallower profile with an exponent -2 in a disc with sub-Eddington accretion rate compared to a similar disc, but without radiation, where its surface density slope is -3 independent of the accretion rate. We then investigate gravitational stability of the disc when the stress parameter reaches to its critical value. In order to self-consistently determine the fragmentation boundary, however, it is shown that the critical value of the stress parameter is a power-law function of the ratio of gas pressure and the total pressure and its exponent is around 1.7. We also estimate the maximum mass of the central black hole using our analytical solutions.

  6. Analytic approach to nonlinear hydrodynamic instabilities driven by time-dependent accelerations

    SciTech Connect

    Mikaelian, K O

    2009-09-28

    We extend our earlier model for Rayleigh-Taylor and Richtmyer-Meshkov instabilities to the more general class of hydrodynamic instabilities driven by a time-dependent acceleration g(t) . Explicit analytic solutions for linear as well as nonlinear amplitudes are obtained for several g(t)'s by solving a Schroedinger-like equation d{sup 2}{eta}/dt{sup 2} - g(t)kA{eta} = 0 where A is the Atwood number and k is the wavenumber of the perturbation amplitude {eta}(t). In our model a simple transformation k {yields} k{sub L} and A {yields} A{sub L} connects the linear to the nonlinear amplitudes: {eta}{sup nonlinear} (k,A) {approx} (1/k{sub L})ln{eta}{sup linear} (k{sub L}, A{sub L}). The model is found to be in very good agreement with direct numerical simulations. Bubble amplitudes for a variety of accelerations are seen to scale with s defined by s = {integral} {radical}g(t)dt, while spike amplitudes prefer scaling with displacement {Delta}x = {integral}[{integral}g(t)dt]dt.

  7. Investigation of MHD instabilities and their dependence on plasma rotation in KSTAR*

    NASA Astrophysics Data System (ADS)

    Park, Y. S.; Sabbagh, S. A.; Berkery, J. W.; Bialek, J. M.; Jeon, Y. M.; Hahn, S. H.; Kim, J.; You, K.-I.; Lee, S. G.; Bak, J. G.; Lee, K. D.; Ko, W. H.; Bae, Y. S.

    2011-10-01

    A goal of the Korea Superconducting Tokamak Advanced Research (KSTAR) is to perform physics studies in support of ITER. With co-directed neutral beam injection, one expected difference between KSTAR and ITER is the degree and profile of the plasma rotation, which affects plasma stability. The present work examines instabilities that exist in KSTAR under plasma rotation conditions spanning the entire KSTAR operational space. Mode characteristics measured by electron cyclotron emission are compared to values computed from reconstructed plasma equilibria. Frequencies of the modes tied to plasma rotation are compared to measurements from an X-ray crystal spectrometer and charge exchange recombination spectroscopy. A first experiment producing non-resonant alteration of the plasma rotation profile by neoclassical toroidal viscosity will be attempted to access a low rotation operating space most applicable to ITER and examine the dependence of beta-limiting instabilities on rotation and rotation shear. Proximity of this new operational regime to MHD stability limits will be examined, as well as implications for n = 1 feedback stabilization planned for future KSTAR operation. Work supported by U.S. DOE grant DE-FG02-99ER54524.

  8. Analytic approach to nonlinear hydrodynamic instabilities driven by time-dependent accelerations

    SciTech Connect

    Mikaelian, Karnig O.

    2010-01-15

    We extend our earlier model for Rayleigh-Taylor and Richtmyer-Meshkov instabilities to the more general class of hydrodynamic instabilities driven by a time-dependent acceleration g(t). Explicit analytic solutions for linear as well as nonlinear amplitudes are obtained for several g(t)s by solving a Schroedinger-like equation d{sup 2}eta/dt{sup 2}-g(t)kAeta=0, where A is the Atwood number and k is the wave number of the perturbation amplitude eta(t). In our model a simple transformation k->k{sub L} and A->A{sub L} connects the linear to the nonlinear amplitudes: eta{sup nonlinear}(k,A)approx(1/k{sub L})ln eta{sup linear}(k{sub L},A{sub L}). The model is found to be in very good agreement with direct numerical simulations. Bubble amplitudes for a variety of accelerations are seen to scale with s defined by s=integralsq root(g(t))dt, while spike amplitudes prefer scaling with displacement DELTAx=integral[integralg(t)dt]dt.

  9. Compensatory Proliferation in Drosophila Imaginal Discs Requires Dronc-Dependent p53 Activity

    PubMed Central

    Wells, Brent S.; Yoshida, Eri; Johnston*, Laura A.

    2006-01-01

    Summary Background The p53 transcription factor directs a transcriptional program that determines whether a cell lives or dies after DNA damage. Animal survival after extensive cellular damage often requires that lost tissue be replaced through compensatory growth or regeneration. In Drosophila, damaged imaginal disc cells can induce the proliferation of neighboring viable cells, but how this is controlled is not clear. Here we provide evidence that Drosophila p53 (dp53) has a previously unidentified role in coordinating the compensatory growth response to tissue damage. Results We find that dp53, the sole p53 ortholog in Drosophila, is required for each component of the response to cellular damage, including two separate cell-cycle arrests, changes in patterning gene expression, cell proliferation, and growth. We demonstrate that these processes are regulated by dp53 in a manner that is independent of DNA-damage sensing but that requires the initiator caspase Dronc. Our results indicate that once induced, dp53 amplifies and sustains the response through a positive feedback loop with Dronc and the apoptosis-inducing factors Hid and Reaper. Conclusions How cell death and cell proliferation are coordinated during development and after stress is a fundamental question that is critical for an understanding of growth regulation. Our data suggest that dp53 may carry out an ancestral function that promotes animal survival through the coordination of responses leading to compensatory growth after tissue damage. PMID:16920621

  10. The time-dependent behaviour of a spinning disc on a rotating planet: A model for geophysical vortex motion

    NASA Astrophysics Data System (ADS)

    McDonald, N. Robb

    A recent theory of Nycander (1996) establishing the analogy between the steady westward drift of geophysical vortices and the precession of a rigid-body (in particular a disc spinning about its symmetry axis) is rederived within a Lagrangian framework. This formulation allows the time-dependent properties (e.g., trajectory, spin etc.) of the rigidbody, represented by three coupled ODEs, to be studied. Numerical results for a variety of initial zonal velocities and latitudes are presented. Typically the trajectory consists of a mean westward precession coupled with periodic behaviour which, in the terminology of rigid-body dynamics, is known as nutation. In the limit that -plane physics are appropriate, it is shown that the nutation is exactly analogous to harmonic inertial oscillations at the local Coriolis frequency.

  11. Size-dependent axisymmetric vibration of functionally graded circular plates in bifurcation/limit point instability

    NASA Astrophysics Data System (ADS)

    Ashoori, A. R.; Vanini, S. A. Sadough; Salari, E.

    2017-04-01

    In the present paper, vibration behavior of size-dependent functionally graded (FG) circular microplates subjected to thermal loading are carried out in pre/post-buckling of bifurcation/limit-load instability for the first time. Two kinds of frequently used thermal loading, i.e., uniform temperature rise and heat conduction across the thickness direction are considered. Thermo-mechanical material properties of FG plate are supposed to vary smoothly and continuously throughout the thickness based on power law model. Modified couple stress theory is exploited to describe the size dependency of microplate. The nonlinear governing equations of motion and associated boundary conditions are extracted through generalized form of Hamilton's principle and von-Karman geometric nonlinearity for the vibration analysis of circular FG plates including size effects. Ritz finite element method is then employed to construct the matrix representation of governing equations which are solved by two different strategies including Newton-Raphson scheme and cylindrical arc-length method. Moreover, in the following a parametric study is accompanied to examine the effects of the several parameters such as material length scale parameter, temperature distributions, type of buckling, thickness to radius ratio, boundary conditions and power law index on the dimensionless frequency of post-buckled/snapped size-dependent FG plates in detail. It is found that the material length scale parameter and thermal loading have a significant effect on vibration characteristics of size-dependent circular FG plates.

  12. Sub-parsec-scale dynamics of a dusty gas disc exposed to anisotropic AGN radiation with frequency-dependent radiative transfer

    NASA Astrophysics Data System (ADS)

    Namekata, Daisuke; Umemura, Masayuki

    2016-07-01

    We explore the gas dynamics near the dust sublimation radius of active galactic nucleus (AGN). For the purpose, we perform axisymmetric radiation hydrodynamic simulations of a dusty gas disc of radius ≈1 pc around a supermassive black hole of mass 107 M⊙ taking into account (1) anisotropic radiation of accretion disc, (2) X-ray heating by corona, (3) radiative transfer of infrared (IR) photons re-emitted by dust, (4) frequency dependence of direct and IR radiations, and (5) separate temperatures for gas and dust. As a result, we find that for Eddington ratio ≈0.77, a nearly neutral, dense ({≈ } 10^{6-8}cm^{-3}), geometrically thin (h/r < 0.06) disc forms with a high-velocity (≈200 ˜ 3000 km s-1) dusty outflow launched from the disc surface. The disc temperature is determined by the balance between X-ray heating and various cooling, and the disc is almost supported by thermal pressure. Contrary to Krolik (2007), the radiation pressure by IR photons is not effective to thicken the disc, but rather compresses it. Thus, it seems difficult for a radiation-supported, geometrically thick, obscuring torus to form near the dust sublimation radius as far as the Eddington ratio is high (˜1). The mass outflow rate is 0.05-0.1M_{⊙} yr^{-1} and the column density of the outflow is NH ≲ 1021 cm-2. To explain observed type-II AGN fraction, it is required that outflow gas is extended to larger radii (r ≳ 10 pc) or that a denser dusty wind is launched from smaller radii (r ˜ 104 Rg).

  13. Myotonic dystrophy: Size- and sex-dependent dynamics of CTG meiotic instability, and somatic mosaicism

    SciTech Connect

    Lavedan, C.; Rabes, J.P.; Duros, C.; Savoy, D. ); Hofmann-Radvanyi, H.; Dehaupas, I.; Luce, S.; Junien, C. Hopital A. Pare, Boulogne ); Shelbourne, P.; Johnson, K. )

    1993-05-01

    Myotonic dystrophy (DM) is a progressive neuromuscular disorder which results from elongations of an unstable (CTG)n repeat, located in the 3' untranslated region of the DM gene. A correlation has been demonstrated between the increase in the repeat number of this sequence and the severity of the disease. However, the clinical status of patients cannot be unambiguously ascertained solely on the basis of the number of CTG repeats. Moreover, the exclusive maternal inheritance of the congenital form remains unexplained. The authors observation of differently sized repeats in various DM tissues from the same individual may explain why the size of the mutation observed in lymphocytes does not necessarily correlate with the severity and nature of symptoms. Through a molecular and genetic study of 142 families including 418 DM patients, the authors have investigated the dynamics of the CTG repeat meiotic instability. A positive correlation between the size of the repeat and the intergenerational enlargement was observed similarly through male and female meioses for l[le]0.5-kb CTG sequences. Beyond 0.5 kb, the intergenerational variation was more important through female meioses, whereas a tendency to compression was observed almost exclusively in male meioses, for [ge] 1.5-kb fragments. This implies a size- and sex-dependent meiotic instability. Moreover, segregation analysis supports the hypothesis of a maternal as well as a familial predisposition for the occurrence of the congenital form. Finally, this analysis reveals a significant excess of transmitting grandfathers partially accounted for by increased fertility in affected males. 23 refs., 7 figs.

  14. Planet-disc interaction in laminar and turbulent discs

    NASA Astrophysics Data System (ADS)

    Stoll, Moritz H. R.; Picogna, Giovanni; Kley, Wilhelm

    2017-07-01

    In weakly ionised discs turbulence can be generated through the vertical shear instability (VSI). Embedded planets are affected by a stochastic component in the torques acting on them, which can impact their migration. In this work we study the interplay between a growing planet embedded in a protoplanetary disc and the VSI turbulence. We performed a series of 3D hydrodynamical simulations for locally isothermal discs with embedded planets in the mass range from 5 to 100 Earth masses. We study planets embedded in an inviscid disc that is VSI unstable, becomes turbulent, and generates angular momentum transport with an effective α = 5 × 10-4. This is compared to the corresponding viscous disc using exactly this α-value. In general we find that the planets have only a weak impact on the disc turbulence. Only for the largest planet (100 M⊕) does the turbulent activity become enhanced inside of the planet. The depth and width of a gap created by the more massive planets (30,100 M⊕) in the turbulent disc equal exactly that of the corresponding viscous case, leading to very similar torque strengths acting on the planet, with small stochastic fluctuations for the VSI disc. At the gap edges vortices are generated that are stronger and longer-lived in the VSI disc. Low mass planets (with Mp ≤ 10 M⊕) do not open gaps in the disc in either case, but generate for the turbulent disc an overdensity behind the planet that exerts a significant negative torque. This can boost the inward migration in VSI turbulent discs well above the Type I rate. Owing to the finite turbulence level in realistic 3D discs the gap depth will always be limited and migration will not stall in inviscid discs.

  15. Seed power dependence of mode instabilities in high-power fiber amplifiers

    NASA Astrophysics Data System (ADS)

    Tao, Rumao; Wang, Xiaolin; Zhou, Pu; Liu, Zejin

    2017-06-01

    A semi-analytical model of stimulated thermal Rayleigh scattering, which assumes that there is a frequency offset between the fundamental mode and the high-order mode at the input of the amplifier, has been employed to study the effects of seed power on thermal-induced mode instability. Both the effects of gain saturation and photodarkening have been taken into consideration. The dependence of the threshold power and the maximal coupling frequency on various seed powers has been investigated when different parameters of fiber amplifier systems, such as the core/pump cladding diameter, and the level of photodarkening, are changed. The nonlinear dependence of the threshold at lower seed powers is mainly ascribed to the influence of gain saturation, while the reduction behavior of the threshold at higher seed powers is put down to the effects of photodarkening. The maximal coupling frequency is shown to vary with different parameters of fiber amplifier systems, such as seed powers, the level of the photodarkening, and core/pump cladding diameters. Comparing the results with the recently published experimental results, reveals that the experimental observation can be explained within this framework.

  16. A novel ATM-dependent checkpoint defect distinct from loss of function mutation promotes genomic instability in melanoma.

    PubMed

    Spoerri, Loredana; Brooks, Kelly; Chia, KeeMing; Grossman, Gavriel; Ellis, Jonathan J; Dahmer-Heath, Mareike; Škalamera, Dubravka; Pavey, Sandra; Burmeister, Bryan; Gabrielli, Brian

    2016-05-01

    Melanomas have high levels of genomic instability that can contribute to poor disease prognosis. Here, we report a novel defect of the ATM-dependent cell cycle checkpoint in melanoma cell lines that promotes genomic instability. In defective cells, ATM signalling to CHK2 is intact, but the cells are unable to maintain the cell cycle arrest due to elevated PLK1 driving recovery from the arrest. Reducing PLK1 activity recovered the ATM-dependent checkpoint arrest, and over-expressing PLK1 was sufficient to overcome the checkpoint arrest and increase genomic instability. Loss of the ATM-dependent checkpoint did not affect sensitivity to ionizing radiation demonstrating that this defect is distinct from ATM loss of function mutations. The checkpoint defective melanoma cell lines over-express PLK1, and a significant proportion of melanomas have high levels of PLK1 over-expression suggesting this defect is a common feature of melanomas. The inability of ATM to impose a cell cycle arrest in response to DNA damage increases genomic instability. This work also suggests that the ATM-dependent checkpoint arrest is likely to be defective in a higher proportion of cancers than previously expected. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  17. The formation of the Hubble sequence of disc galaxies: the effects of early viscous evolution

    NASA Astrophysics Data System (ADS)

    Zhang, Bing; Wyse, Rosemary F. G.

    2000-04-01

    We investigate a model of disc galaxies whereby viscous evolution of the gaseous disc drives material inwards to form a protobulge. We start from the standard picture of disc formation through the settling of gas into a dark halo potential well, with the disc initially coming into centrifugal equilibrium with detailed conservation of angular momentum. We derive generic analytic solutions for the disc-halo system after adiabatic compression of the dark halo, with free choice of the input virialized dark halo density profile and of the specific angular momentum distribution. We derive limits on the final density profile of the halo in the central regions. Subsequent viscous evolution of the disc is modelled by a variation of the specific angular momentum distribution of the disc, providing analytic solutions to the final disc structure. The assumption that the viscous evolution time-scale and the star formation time-scale are similar leads to predictions of the properties of the stellar components. Focusing on small `exponential' bulges, i.e., ones that may be formed through a disc instability, we investigate the relationship between the assumed initial conditions, such as halo `formation', or assembly, redshift zf, spin parameter λ, baryonic fraction F, and final disc properties such as global star formation time-scale, gas fraction, and bulge-to-disc ratio. We find that the present properties of discs, such as the scalelength, are compatible with a higher initial formation redshift if the redistribution by viscous evolution is included than if it is ignored. We also quantify the dependence of final disc properties on the ratio Fλ, thus including the possibility that the baryonic fraction varies from galaxy to galaxy, as perhaps may be inferred from the observations.

  18. Quantization and instability of the damped harmonic oscillator subject to a time-dependent force

    SciTech Connect

    Majima, H. Suzuki, A.

    2011-12-15

    We consider the one-dimensional motion of a particle immersed in a potential field U(x) under the influence of a frictional (dissipative) force linear in velocity (-{gamma}x) and a time-dependent external force (K(t)). The dissipative system subject to these forces is discussed by introducing the extended Bateman's system, which is described by the Lagrangian: L=mxy-U(x+1/2 y)+U(x-1/2 y)+({gamma})/2 (xy-yx)-xK(t)+yK(t), which leads to the familiar classical equations of motion for the dissipative (open) system. The equation for a variable y is the time-reversed of the x motion. We discuss the extended Bateman dual Lagrangian and Hamiltonian by setting U(x{+-}y/2)=1/2 k(x{+-}y/2){sup 2} specifically for a dual extended damped-amplified harmonic oscillator subject to the time-dependent external force. We show the method of quantizing such dissipative systems, namely the canonical quantization of the extended Bateman's Hamiltonian H. The Heisenberg equations of motion utilizing the quantized Hamiltonian H surely lead to the equations of motion for the dissipative dynamical quantum systems, which are the quantum analog of the corresponding classical systems. To discuss the stability of the quantum dissipative system due to the influence of an external force K(t) and the dissipative force, we derived a formula for transition amplitudes of the dissipative system with the help of the perturbation analysis. The formula is specifically applied for a damped-amplified harmonic oscillator subject to the impulsive force. This formula is used to study the influence of dissipation such as the instability due to the dissipative force and/or the applied impulsive force. - Highlights: > A method of quantizing dissipative systems is presented. > In order to obtain the method, we apply Bateman's dual system approach. > A formula for a transition amplitude is derived. > We use the formula to study the instability of the dissipative systems.

  19. Functional mapping of the translation-dependent instability element of yeast MATalpha1 mRNA.

    PubMed Central

    Hennigan, A N; Jacobson, A

    1996-01-01

    The determinants of mRNA stability include specific cis-acting destabilizing sequences located within mRNA coding and noncoding regions. We have developed an approach for mapping coding-region instability sequences in unstable yeast mRNAs that exploits the link between mRNA translation and turnover and the dependence of nonsense-mediated mRNA decay on the activity of the UPF1 gene product. This approach, which involves the systematic insertion of in-frame translational termination codons into the coding sequence of a gene of interest in a upf1delta strain, differs significantly from conventional methods for mapping cis-acting elements in that it causes minimal perturbations to overall mRNA structure. Using the previously characterized MATalpha1 mRNA as a model, we have accurately localized its 65-nucleotide instability element (IE) within the protein coding region. Termination of translation 5' to this element stabilized the MATalpha1 mRNA two- to threefold relative to wild-type transcripts. Translation through the element was sufficient to restore an unstable decay phenotype, while internal termination resulted in different extents of mRNA stabilization dependent on the precise location of ribosome stalling. Detailed mutagenesis of the element's rare-codon/AU-rich sequence boundary revealed that the destabilizing activity of the MATalpha1 IE is observed when the terminal codon of the element's rare-codon interval is translated. This region of stability transition corresponds precisely to a MATalpha1 IE sequence previously shown to be complementary to 18S rRNA. Deletion of three nucleotides 3' to this sequence shifted the stability boundary one codon 5' to its wild-type location. Conversely, constructs containing an additional three nucleotides at this same location shifted the transition downstream by an equivalent sequence distance. Our results suggest a model in which the triggering of MATalpha1 mRNA destabilization results from establishment of an interaction

  20. The Gaia-ESO Survey: New constraints on the Galactic disc velocity dispersion and its chemical dependencies

    NASA Astrophysics Data System (ADS)

    Guiglion, G.; Recio-Blanco, A.; de Laverny, P.; Kordopatis, G.; Hill, V.; Mikolaitis, Š.; Minchev, I.; Chiappini, C.; Wyse, R. F. G.; Gilmore, G.; Randich, S.; Feltzing, S.; Bensby, T.; Flaccomio, E.; Koposov, S. E.; Pancino, E.; Bayo, A.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Morbidelli, L.; Sacco, G. G.; Ruchti, G.; Worley, C. C.; Zaggia, S.

    2015-11-01

    Context. Understanding the history and the evolution of the Milky Way is one of the main goals of modern astrophysics. In particular, the formation of the Galactic disc is a key problem of Galactic archaeology. Aims: We study the velocity dispersion behaviour of Galactic disc stars as a function of the [Mg/Fe] ratio, which for small metallicity bins can be used as a proxy of relative age. This key relation is essential to constrain the formation mechanisms of the disc stellar populations as well as the cooling and settling processes. Methods: We used the recommended parameters and chemical abundances of 7800 FGK Milky Way field stars from the second internal data release of the Gaia-ESO spectroscopic Survey. These stars were observed with the GIRAFFE spectrograph (HR10 and HR21 setups), and cover a large spatial volume in the intervals 6 disc sequence in the [Mg/Fe] vs. [Fe/H] plane. Results: From analysing the Galactocentric velocity of the stars for the thin disc, we find a weak positive correlation between Vφ and [Fe/H] that is due to a slowly rotating [Fe/H]-poor tail. For the thick disc stars, a strong correlation with [Fe/H] and [Mg/Fe] is established. In addition, we have detected an inversion of the velocity dispersion trends with [Mg/Fe] for thick-disc stars with [Fe/H] < -0.10 dex and [Mg/Fe] > +0.20 dex for the radial component. First, the velocity dispersion increases with [Mg/Fe] at all [Fe/H] ratios for the thin-disc stars, and then it decreases for the thick-disc population at the highest [Mg/Fe] abundances. Similar trends are observed for several bins of [Mg/Fe] within the errors for the azimuthal velocity dispersion, while a continuous increase with [Mg/Fe] is observed for the vertical velocity dispersion. The velocity dispersion decrease agrees with previous measurements of the RAVE survey, although it is observed here for a greater metallicity

  1. The origin of thick discs

    NASA Astrophysics Data System (ADS)

    Comerón, Sébastien

    2015-03-01

    Thick discs are defined to be disc-like components with a scale height larger than that of the classical discs. They are ubiquitous (Yoachim & Dalcanton 2006; Comerón et al. 2011a), they are made of mostly old and metal-poor stars and are most easily detected in close to edge-on galaxies. Their origin has been considered mysterious and several formation theories have been proposed: • The thick disc being formed secularly by thin disc stars heated by disc overdensities such as giant molecular clouds or spiral arms (Villumsen 1985, ApJ, 290, 75) and by stars moved outwards from their original orbits by radial migration mechanisms (Schönrich & Binney 2009). • The thick disc being formed by the heating of the thin disc by satellites (Quinn et al. 1993) and the tidal stripping of them (Abadi et al. 2003). • The thick disc being formed fast and already thick at high redshift in an highly unstable disc. Inside that thick disc, a thin disc would form afterwards as suggested by Elemgreen & Elmegreen (2006). • The thick disc being formed originally thick at high redshift by the merger of gas-rich protogalactic fragments and a thin disc forming afterwards within it (Brook et al. 2007). The first mechanism is a secular evolution mechanism. The time-scale of the second one is dependent on the merger history of the main galaxy. In the two last mechanisms, the thick disc forms already thick in a short time-scale at high redshift. Recent Milky Way studies, (see, e.g., Bovy et al. 2012), have shown indications that there is no discontinuity between the thin and the thick disc chemical and kinematic properties. Instead, those studies indicate the presence of a monotonic distribution of disc thicknesses. This would suggest a secular origin for the Milky Way thick disc. Studies in external galaxies (Yoachim & Dalcanton 2006; Comerón et al. 2011b), have shown that low-mass disc galaxies have thick disc relative masses much larger than those found in large-mass galaxies

  2. Formaldehyde-Induced Genome Instability is Suppressed by an XPF-dependent Pathway

    PubMed Central

    Kumari, Anuradha; Lim, Yun Xin; Newell, Amy Hanlon; Olson, Susan B.; McCullough, Amanda K.

    2011-01-01

    Formaldehyde is a reactive chemical that is commonly used in the production of industrial, laboratory, household, and cosmetic products. The causal association between formaldehyde exposure and increased incidence of cancer led the International Agency for Research on Cancer to classify formaldehyde as a carcinogen. Formaldehyde-induced DNA-protein crosslinks (DPCs) elicit responses involving nucleotide excision repair (NER) and homologous recombination (HR) repair pathways; however, little is known about the cellular and genetic changes that subsequently lead to formaldehyde-induced genotoxic and cytotoxic effects. Herein, investigations of genes that modulate the cytotoxic effects of formaldehyde exposure revealed that of five NER-deficient Chinese Hamster Ovary (CHO) cell lines tested, XPF- and ERCC1-deficient cells were most sensitive to formaldehyde treatment as compared to wild-type cells. Cell cycle analyses revealed that formaldehyde-treated XPF-deficient cells exhibited an immediate G2/M arrest that was associated with altered cell ploidy and apoptosis. Additionally, an elevated number of DNA double-strand breaks (DSBs), chromosomal breaks and radial formation were also observed in XPF-deficient cells following formaldehyde treatment. Formaldehyde-induced DSBs occurred in a replication-dependent, but an XPF-independent manner. However, delayed DSB repair was observed in the absence of XPF function. Collectively, our findings highlight the role of an XPF-dependent pathway in mitigating the sensitivity to formaldehyde-induced DNA damage as evidenced by the increased genomic instability and reduced cell viability in an XPF-deficient background. In addition, centrosome and microtubule abnormalities, as well as enlarged nuclei, caused by formaldehyde exposure are also demonstrated in a repair-proficient cell line. PMID:22186232

  3. Laboratory experiment of liquefaction under vertical vibration: parameter dependence of the resulting instabilities

    NASA Astrophysics Data System (ADS)

    Yasuda, N.; Sumita, I.

    2013-12-01

    (Transition) whose amplitude grows and a flame structure forms (Flame). We find that the critical acceleration for the formation of a flame structure is of the order of (Δρ/ρ)g, where Δρ is the particle-water density difference, ρ is the particle density, and g is the gravitational acceleration. We apply the results of linear stability analysis for superimposed viscous fluids to our experiments. We find that the growth rate and the wavelength of the instability can be explained if the effective layer thickness of the lower layer is of the order of 1 mm. This suggests that only the uppermost part of the lower layer is mobile. Further detailed parameter dependence and their analyses will be presented in the poster.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. The dependence of the AV prior for SN Ia on host mass and disc inclination

    NASA Astrophysics Data System (ADS)

    Holwerda, B. W.; Keel, W. C.; Kenworthy, M. A.; Mack, K. J.

    2015-08-01

    Type Ia supernovae (SNe Ia) are used as `standard candles' for cosmological distance scales. To fit their light-curve shape-absolute luminosity relation, one needs to assume an intrinsic colour and a likelihood of host galaxy extinction or a convolution of these, a colour distribution prior. The host galaxy extinction prior is typically assumed to be an exponential drop-off for the current supernova programmes (P(A_V) ∝ e^{-A_V/τ_0}). We explore the validity of this prior using the distribution of extinction values inferred when two galaxies accidentally overlap (an occulting galaxy pair). We correct the supernova luminosity distances from the SDSS-III supernova projects (SDSS-SN) by matching the host galaxies to one of three templates from occulting galaxy pairs based on the host galaxy mass and the AV-bias-prior-scale (τ0) relation from Jha et al. We find that introducing an AV prior that depends on host mass results in lowered luminosity distances for the SDSS-SN on average but it does not reduce the scatter in individual measurements. This points, in our view, to the need for many more occulting galaxy templates to match to SN Ia host galaxies to rule out this possible source of scatter in the SN Ia distance measurements. We match occulting galaxy templates based on both mass and projected radius and we find that one should match by stellar mass first with radius as a secondary consideration. We discuss the caveats of the current approach: the lack of enough radial coverage, the small sample of priors (occulting pairs with HST data), the effect of gravitationally interacting as well as occulting pairs, and whether an exponential distribution is appropriate. Our aim is to convince the reader that a library of occulting galaxy pairs observed with HST will provide sufficient priors to improve (optical) SN Ia measurements to the next required accuracy in cosmology.

  6. Haplotype transmission analysis provides evidence of association for DISC1 to schizophrenia and suggests sex-dependent effects.

    PubMed

    Hennah, William; Varilo, Teppo; Kestilä, Marjo; Paunio, Tiina; Arajärvi, Ritva; Haukka, Jari; Parker, Alex; Martin, Rory; Levitzky, Steve; Partonen, Timo; Meyer, Joanne; Lönnqvist, Jouko; Peltonen, Leena; Ekelund, Jesper

    2003-12-01

    We have previously reported a linkage peak on 1q42 in a Finnish schizophrenia sample. In this study we genotyped 28 single nucleotide polymorphisms (SNPs) from 1q42 covering the three candidate genes TRAX, DISC1 and DISC2, using a study sample of 458 Finnish families ascertained for schizophrenia. Two-point and haplotype association analysis revealed a significant region of interest within the DISC1 gene. A common haplotype (HEP3) was observed to be significantly under-transmitted to affected individuals (P=0.0031). HEP3 represents a two SNP haplotype spanning from intron 1 to exon 2 of DISC1. This haplotype also displayed sex differences in transmission distortion, the under-transmission being significant only to affected females (P=0.00024). Three other regions of interest were observed in the TRAX and DISC genes. However, analysis of only those families with complete genotype information specifically highlights the HEP3 haplotype as a true observation. The finding of a common under-transmitted SNP haplotype might imply that this particular allele offers some protection from the development of schizophrenia. Analysis of component-traits of schizophrenia, derived from the Operational Criteria Checklist of Psychotic Illness (OCCPI), displayed association of HEP3 to features of the general phenotype of schizophrenia, including traits representing delusions, hallucinations and negative symptoms. This study provides further evidence for the hypothesis that the DISC1 gene is involved in the aetiology of schizophrenia, and implies a putative sex difference for the effect of the gene. Our findings would also encourage more detailed analyses of the effect of DISC1 on the component-traits of schizophrenia.

  7. Coevolution of binaries and circumbinary gaseous discs

    NASA Astrophysics Data System (ADS)

    Fleming, David P.; Quinn, Thomas R.

    2017-01-01

    The recent discoveries of circumbinary planets by Kepler raise questions for contemporary planet formation models. Understanding how these planets form requires characterizing their formation environment, the circumbinary protoplanetary disc and how the disc and binary interact and change as a result. The central binary excites resonances in the surrounding protoplanetary disc which drive evolution in both the binary orbital elements and in the disc. To probe how these interactions impact binary eccentricity and disc structure evolution, N-body smooth particle hydrodynamics simulations of gaseous protoplanetary discs surrounding binaries based on Kepler 38 were run for 104 binary periods for several initial binary eccentricities. We find that nearly circular binaries weakly couple to the disc via a parametric instability and excite disc eccentricity growth. Eccentric binaries strongly couple to the disc causing eccentricity growth for both the disc and binary. Discs around sufficiently eccentric binaries which strongly couple to the disc develop an m = 1 spiral wave launched from the 1:3 eccentric outer Lindblad resonance which corresponds to an alignment of gas particle longitude of periastrons. All systems display binary semimajor axis decay due to dissipation from the viscous disc.

  8. A 2-DOF microstructure-dependent model for the coupled torsion/bending instability of rotational nanoscanner

    NASA Astrophysics Data System (ADS)

    Keivani, M.; Abadian, N.; Koochi, A.; Mokhtari, J.; Abadyan, M.

    2016-10-01

    It has been well established that the physical performance of nanodevices might be affected by the microstructure. Herein, a two-degree-of-freedom model base on the modified couple stress theory is developed to incorporate the impact of microstructure in the torsion/bending coupled instability of rotational nanoscanner. Effect of microstructure dependency on the instability parameters is determined as a function of the microstructure parameter, bending/torsion coupling ratio, van der Waals force parameter and geometrical dimensions. It is found that the bending/torsion coupling substantially affects the stable behavior of the scanners especially those with long rotational beam elements. Impact of microstructure on instability voltage of the nanoscanner depends on coupling ratio and the conquering bending mode over torsion mode. This effect is more highlighted for higher values of coupling ratio. Depending on the geometry and material characteristics, the presented model is able to simulate both hardening behavior (due to microstructure) and softening behavior (due to torsion/bending coupling) of the nanoscanners.

  9. Magnetic fields in giant planet formation and protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Keith, Sarah Louise

    2015-12-01

    Protoplanetary discs channel accretion onto their host star. How this is achieved is critical to the growth of giant planets which capture their massive gaseous atmosphere from the surrounding flow. Theoretical studies find that an embedded magnetic field could power accretion by hydromagnetic turbulence or torques from a large-scale field. This thesis presents a study of the inuence of magnetic fields in three key aspects of this process: circumplanetary disc accretion, gas flow across gaps in protoplanetary discs, and magnetic-braking in accretion discs. The first study examines the conditions needed for self-consistent accretion driven by magnetic fields or gravitational instability. Models of these discs typically rely on hydromagnetic turbulence as the source of effective viscosity. However, magnetically coupled,accreting regions may be so limited that the disc may not support sufficient inflow. An improved Shakura-Sunyaev ? disc is used to calculate the ionisation fraction and strength of non-ideal effects. Steady magnetically-driven accretion is limited to the thermally ionised, inner disc so that accretion in the remainder of the disc is time-dependent. The second study addresses magnetic flux transport in an accretion gap evacuated by a giant planet. Assuming the field is passively drawn along with the gas, the hydrodynamical simulation of Tanigawa, Ohtsuki & Machida (2012) is used for an a posteriori analysis of the gap field structure. This is used to post-calculate magnetohydrodynamical quantities. This assumption is self-consistent as magnetic forces are found to be weak, and good magnetic coupling ensures the field is frozen into the gas. Hall drift dominates across much of the gap, with the potential to facilitate turbulence and modify the toroidal field according to the global field orientation. The third study considers the structure and stability of magnetically-braked accretion discs. Strong evidence for MRI dead-zones has renewed interest in

  10. On the survival of zombie vortices in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Lesur, Geoffroy R. J.; Latter, Henrik

    2016-11-01

    Recently it has been proposed that the zombie vortex instability (ZVI) could precipitate hydrodynamical activity and angular momentum transport in unmagnetized regions of protoplanetary discs, also known as `dead zones'. In this Letter we scrutinize, with high-resolution 3D spectral simulations, the onset and survival of this instability in the presence of viscous and thermal physics. First, we find that the ZVI is strongly dependent on the nature of the viscous operator. Although the ZVI is easily obtained with hyperdiffusion, it is difficult to sustain with physical (second order) diffusion operators up to Reynolds numbers as high as 107. This sensitivity is probably due to the ZVI's reliance on critical layers, whose characteristic length-scale, structure, and dynamics are controlled by viscous diffusion. Second, we observe that the ZVI is sensitive to radiative processes, and indeed only operates when the Peclet number is greater than a critical value ˜104, or when the cooling time is longer than ˜10Ω-1. As a consequence, the ZVI struggles to appear at R ≳ 0.3 au in standard 0.01 M⊙ T Tauri disc models, though younger more massive discs provide a more hospitable environment. Together these results question the prevalence of the ZVI in protoplanetary discs.

  11. TGFβ and BMP Dependent Cell Fate Changes Due to Loss of Filamin B Produces Disc Degeneration and Progressive Vertebral Fusions

    PubMed Central

    Zieba, Jennifer; Forlenza, Kimberly Nicole; Khatra, Jagteshwar Singh; Sarukhanov, Anna; Duran, Ivan; Rigueur, Diana; Lyons, Karen M.; Cohn, Daniel H.; Merrill, Amy E.; Krakow, Deborah

    2016-01-01

    Spondylocarpotarsal synostosis (SCT) is an autosomal recessive disorder characterized by progressive vertebral fusions and caused by loss of function mutations in Filamin B (FLNB). FLNB acts as a signaling scaffold by linking the actin cytoskleteon to signal transduction systems, yet the disease mechanisms for SCT remain unclear. Employing a Flnb knockout mouse, we found morphologic and molecular evidence that the intervertebral discs (IVDs) of Flnb–/–mice undergo rapid and progressive degeneration during postnatal development as a result of abnormal cell fate changes in the IVD, particularly the annulus fibrosus (AF). In Flnb–/–mice, the AF cells lose their typical fibroblast-like characteristics and acquire the molecular and phenotypic signature of hypertrophic chondrocytes. This change is characterized by hallmarks of endochondral-like ossification including alterations in collagen matrix, expression of Collagen X, increased apoptosis, and inappropriate ossification of the disc tissue. We show that conversion of the AF cells into chondrocytes is coincident with upregulated TGFβ signaling via Smad2/3 and BMP induced p38 signaling as well as sustained activation of canonical and noncanonical target genes p21 and Ctgf. These findings indicate that FLNB is involved in attenuation of TGFβ/BMP signaling and influences AF cell fate. Furthermore, we demonstrate that the IVD disruptions in Flnb–/–mice resemble aging degenerative discs and reveal new insights into the molecular causes of vertebral fusions and disc degeneration. PMID:27019229

  12. Comparison of animal discs used in disc research to human lumbar disc: torsion mechanics and collagen content.

    PubMed

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

    2012-07-01

    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 with the human disc. To aid in the selection of appropriate animal models for disc research by measuring torsional mechanical properties and collagen content. There is lack of data and variability in testing protocols for comparing animal and human disc torsion mechanics and collagen content. 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 discs, and cow, rat, and mouse caudal discs. Collagen content was measured and normalized by dry weight for the same discs except the rat and the mouse. Collagen fiber stretch in torsion was calculated using an analytical model. 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 discs. 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. Disc torsion mechanics are comparable with 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 are useful for selecting and interpreting results for animal disc models. Structural organization of the fiber angle may explain the differences that were noted between species after geometric normalization.

  13. Hysteresis and thermal limit cycles in MRI simulations of accretion discs

    NASA Astrophysics Data System (ADS)

    Latter, H. N.; Papaloizou, J. C. B.

    2012-10-01

    The recurrentoutbursts that characterize low-mass binary systems reflect thermal state changes in their associated accretion discs. The observed outbursts are connected to the strong variation in disc opacity as hydrogen ionizes near 5000 K. This physics leads to accretion disc models that exhibit bistability and thermal limit cycles, whereby the disc jumps between a family of cool and low-accreting states and a family of hot and efficiently accreting states. Previous models have parametrized the disc turbulence via an alpha (or 'eddy') viscosity. In this paper we treat the turbulence more realistically via a suite of numerical simulations of the magnetorotational instability (MRI) in local geometry. Radiative cooling is included via a simple but physically motivated prescription. We show the existence of bistable equilibria and thus the prospect of thermal limit cycles, and in so doing demonstrate that MRI-induced turbulence is compatible with the classical theory. Our simulations also show that the turbulent stress and pressure perturbations are only weakly dependent on each other on orbital times; as a consequence, thermal instability connected to variations in turbulent heating (as opposed to radiative cooling) is unlikely to operate, in agreement with previous numerical results. Our work presents a first step towards unifying simulations of full magnetohydrodynamic turbulence with the correct thermal and radiative physics of the outbursting discs associated with dwarf novae, low-mass X-ray binaries and possibly young stellar objects.

  14. Development of Concentration-Dependent Diffusion Instability in Reactive Miscible Fluids Under Influence of Constant or Variable Inertia

    NASA Astrophysics Data System (ADS)

    Bratsun, Dmitry A.; Stepkina, Olga S.; Kostarev, Konstantin G.; Mizev, Alexey I.; Mosheva, Elena A.

    2016-12-01

    In this work, we focus on the processes which accompany a frontal neutralization reaction occurring between two miscible fluids filling a vertical Hele-Shaw cell. We have found that chemically-induced changes of reagent concentrations coupled with concentration- dependent diffusion (CDD) can produce spatially localized low density areas which are sensitive to the external inertial field. In the case of static gravity we have demonstrated both experimentally and theoretically that it can give rise to the development of perfectly periodic convective structure. This scenario is strikingly different from the irregular density fingering, which is typically observed in the miscible systems. When the system is under the influence of the periodic low-frequency vibrations perpendicular to the reaction front, we found numerically the excitation of a mixed-mode instability combining the double-diffusion instabilities and the Rayleigh-Taylor mechanism of the convection within the low density areas.

  15. Novel Bruch's Membrane Opening Minimum Rim Area Equalizes Disc Size Dependency and Offers High Diagnostic Power for Glaucoma.

    PubMed

    Enders, Philip; Adler, Werner; Schaub, Friederike; Hermann, Manuel M; Dietlein, Thomas; Cursiefen, Claus; Heindl, Ludwig M

    2016-12-01

    The purpose of this study was to assess the diagnostic power of the novel two-dimensional parameter Bruch's membrane opening minimal rim area (BMO-MRA) in spectral-domain optical coherence tomography (SD-OCT) for detection of glaucoma compared to minimal rim width (BMO-MRW) and retinal nerve fiber layer (RNFL) thickness in large and small optic discs. In this case-control, cross-sectional study, 207 eyes of 207 participants, including 89 controls and 97 patients with glaucoma and 21 with ocular hypertension (OHT), with a disc size <1.63 mm2 or >2.43 mm2 underwent SD-OCT, confocal laser scanning tomography (CSLT), visual field testing, and clinical examination. Bruch's membrane opening-MRA BMO-MRW, RNFL thickness of SD-OCT and disc margin rim area (DM-RA) of CSLT were evaluated and analyzed for diagnostic power to detect glaucoma. In healthy eyes with macrodiscs, mean BMO-MRW of 243.14 ± 43.12 μm was significantly smaller than BMO-MRW in microdiscs (338.97 ± 69.39; P < 0.001). Bruch's membrane opening-MRA was comparable between disc size groups with 1.22 ± 0.25 mm2 for macrodiscs and 1.26 ± 0.27 mm2 for microdiscs (P = 0.51), as was RNFL thickness (82.69 ± 15.76 μm versus 78.53 ± 11.01 μm, respectively; P = 0.28). Perimetric mean deviation was -8.7 ± 6.3 dB in glaucoma and -0.6 ± 1.60 dB in OHT patients. Correlation of BMO-MRA and visual field function was rho (ρ) = 0.70 (P < 0.001). Diagnostic power to differentiate glaucoma patients was highest for BMO-MRA. Partial area under the curve (pAUC) for BMO-MRA was 0.14 for specificity between 0.8 and 1.0, exceeding pAUCs of BMO-MRW (P < 0.001), RNFL thickness (P = 0.03), and DM-RA (P = 0.01). Bruch's membrane opening-based minimum rim area measurements offer advantages compared to one-dimensional parameters assessing neuroretinal rim by SD-OCT. In nonglaucomatous eyes, BMO-MRA values seem comparable for the full range of disc sizes. Bruch's membrane opening-MRA surpasses other parameters in diagnostic power

  16. The effects of incremental speed-dependent treadmill training on postural instability and fear of falling in Parkinson's disease.

    PubMed

    Cakit, Burcu Duyur; Saracoglu, Meryem; Genc, Hakan; Erdem, Hatice Rana; Inan, Levent

    2007-08-01

    To detect the effectiveness of incremental speed-dependent treadmill training on postural instability, dynamic balance and fear of falling in patients with idiopathic Parkinson's disease. Randomized controlled trial. Ankara Education and Research Hospital, 2nd PM&R Clinic, Cardiopulmonary Rehabilitation Unit. Fifty-four patients with idiopathic Parkinson's disease in stage 2 or 3 of the Hoehn Yahr staging entered, and 31 patients (21 training, 10 control) had outcome data. Postural instability of patients with Parkinson's disease was assessed using the motor component of the Unified Parkinson's Disease Rating Scale (UPDRS), Berg Balance Test, Dynamic Gait Index and Falls Efficacy Scale. Twenty-one patients with Parkinson's disease participated in an eight-week exercise programme using incremental speed-dependent treadmill training. Before and after the training programme, balance, gait, fear of falling and walking distance and speed on treadmill were assessed in both Parkinson's disease groups. Walking distance and speed on treadmill, UPDRS, Berg Balance Test, Dynamic Gait Index and Falls Efficacy Scale. Initial total walking distance of the training group on treadmill was 266.45 +/- 82.14 m and this was progressively increased to 726.36 +/- 93.1 m after 16 training session (P < 0.001). Tolerated maximum speed of the training group on treadmill at baseline was 1.9 +/- 0.75 km/h and improved to 2.61 +/- 0.77 km/h (P < 0.001). Berg Balance Test, Dynamic Gait Index and Falls Efficacy Scale scores of the training group were improved significantly after the training programme (P < 0.01). There was no significant improvement in any of the outcome measurements in the control group (P > 0.05). Specific exercise programmes using incremental speed-dependent treadmill training may improve mobility, reduce postural instability and fear of falling in patients with Parkinson's disease.

  17. Disc-mass distribution in star-disc encounters

    NASA Astrophysics Data System (ADS)

    Steinhausen, M.; Olczak, C.; Pfalzner, S.

    2012-02-01

    Aims: Investigations of stellar encounters in cluster environments have demonstrated their potential influence on the mass and angular momentum of protoplanetary discs around young stars. We investigated how far the initial surface density in the disc surrounding a young star influences the outcome of an encounter. Methods: The numerical method applied here allows us to determine the mass and angular momentum losses in an encounter for any initial disc-mass distribution. On the basis of a power-law ansatz for the surface density, Σ(r) ∝ r - p, we perform a parameter study of star-disc encounters with different initial disc-mass distributions using N-body simulations. Results: We demonstrate that the shape of the disc-mass distribution has a significant impact on the quantity of the disc-mass and angular momentum losses in star-disc encounters. In particular, the results are most sensitive to how the outer parts of the disc are perturbed by high-mass stars. In contrast, disc-penetrating encounters lead more or less independently of the disc-mass distribution always to large losses. However, maximum losses are generally obtained for initially flat distributed disc material. Based on a parameter study, a fit formula is derived, describing how the relative mass and angular momentum loss depend on the initial disc-mass distribution index p. Encounters generally lead to a steepening of the density profile of the disc. The resulting profiles can have a r-2-dependence or an even steeper one that is independent of the initial distribution of the disc material. Conclusions: From observations, the initial density distribution in discs remains unconstrained, hence the strong dependence on the initial density distribution that we find here might require a revision of the effect of encounters in young stellar clusters. The steep surface density distributions induced by some encounters might be a prerequisite to the formation of planetary systems similar to our own Solar

  18. Disk instability and the time-dependent X-ray emission from the intermediate polar GK Persei

    NASA Technical Reports Server (NTRS)

    Yi, Insu; Kim, Soon-Wook; Vishniac, Ethan T.; Wheeler, J. C.

    1992-01-01

    The correlation between the disk instability model for the 1981-1989 optical outbursts of the intermediate polar GK Per and the accompanying X-ray emission is examined, and the self-consistency of the combined optical-X-ray model is investigated. Special attention is given to the nature of the transition in the X-ray emission due to the time-dependent accretion rates in the simple column accretion model. The large variation in the efficiency of hard X-ray production is explained.

  19. Disk instability and the time-dependent X-ray emission from the intermediate polar GK Persei

    NASA Technical Reports Server (NTRS)

    Yi, Insu; Kim, Soon-Wook; Vishniac, Ethan T.; Wheeler, J. C.

    1992-01-01

    The correlation between the disk instability model for the 1981-1989 optical outbursts of the intermediate polar GK Per and the accompanying X-ray emission is examined, and the self-consistency of the combined optical-X-ray model is investigated. Special attention is given to the nature of the transition in the X-ray emission due to the time-dependent accretion rates in the simple column accretion model. The large variation in the efficiency of hard X-ray production is explained.

  20. RETRACTION: Unsteady flow and heat transfer of viscous incompressible fluid with temperature-dependent viscosity due to a rotating disc in a porous medium

    NASA Astrophysics Data System (ADS)

    Attia, H. A.

    2007-04-01

    It has come to the attention of the Institute of Physics that this article should not have been submitted for publication owing to its plagiarism of an earlier paper (Hossain A, Hossain M A and Wilson M 2001 Unsteady flow of viscous incompressible fluid with temperature-dependent viscosity due to a rotating disc in presence of transverse magnetic field and heat transfer Int. J. Therm. Sci. 40 11-20). Therefore this article has been retracted by the Institute of Physics and by the author, Hazem Ali Attia.

  1. Nonlocal size dependency in nonlinear instability of axially loaded exponential shear deformable FG-CNT reinforced nanoshells under heat conduction

    NASA Astrophysics Data System (ADS)

    Sahmani, S.; Fattahi, A. M.

    2017-05-01

    The present study deals with size-dependent nonlinear instability characteristics of functionally graded carbon nanotube (FG-CNT) reinforced composite shells at nanoscale subjected to axial compression combined with through-thickness heat conduction. To take size dependency into account, Eringen's nonlocal continuum elasticity is incorporated to a novel shear deformation shell theory including a refined exponential distribution for transverse shear strain. In addition to the uniform distribution (UD) of CNT reinforcements, three FG patterns are also considered, namely FG-A, FG-V and FG-X. Also, on the basis of polynomial series, the temperature variation due to the through-thickness heat conduction is estimated. Via a perturbation-based boundary layer-type solving procedure, explicit expressions for nonlocal equilibrium curves are proposed relevant to the prebuckling and postbuckling regimes of FG-CNT exponential shear deformable nanoshells with temperature-dependent and temperature-independent material properties. It is observed that by taking the nonlocality size effect into consideration, the influence of the through-thickness heat conduction on the nonlinear axial instability response of FG-CNT reinforced nanoshells becomes more significant.

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

    PubMed Central

    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

  3. Sound velocities in highly oriented pyrolytic graphite shocked to 18 GPa: Orientational order dependence and elastic instability

    SciTech Connect

    Lucas, Marcel; Winey, J. M.; Gupta, Y. M.

    2015-12-28

    Previous reports of rapid phase transformation above 18 GPa [Erskine and Nellis, Nature 349, 317 (1991)] and large elastic waves below 18 GPa [Lucas et al., J. Appl. Phys. 114, 093515 (2013)] for shock-compressed ZYB-grade highly-oriented pyrolytic graphite (HOPG), but not for less oriented ZYH-grade HOPG, indicated a link between the orientational order dependence of the HOPG response above and below the phase transformation stress. To gain insight into this link and into the mechanical response of HOPG shocked to peak stresses approaching the phase transformation onset, the compressibility of ZYB- and ZYH-grade HOPG in the shocked state was examined using front surface impact experiments. Particle velocity histories and sound velocities were measured for peak stresses reaching 18 GPa. Although the locus of the measured peak stress-particle velocity states is indistinguishable for the two grades of HOPG, the measured sound velocities in the peak state reveal significant differences between the two grades. Specifically, 1) The measured sound velocities are somewhat higher for ZYH-grade HOPG, compared to ZYB-grade HOPG. 2) The measured sound velocities for ZYH-grade HOPG increase smoothly with compression, whereas those for ZYB-2 grade HOPG exhibit a significant reduction in the compression dependence from 12 GPa to 17 GPa and an abrupt increase from 17 GPa to 18 GPa. 3) The longitudinal moduli, determined from the measured sound velocities, are smaller than the calculated bulk moduli for ZYB-grade HOPG shocked to peak stresses above 15 GPa, indicating the onset of an elastic instability. The present findings demonstrate that the softening of the longitudinal modulus (or elastic instability) presented here is linked to the large elastic waves and the rapid phase transformation reported previously – all observed only for shocked ZYB-grade HOPG. The elastic instability in shocked ZYB-grade HOPG is likely a precursor to the rapid phase transformation observed above

  4. The viscosity parameter α and the properties of accretion disc outbursts in close binaries

    NASA Astrophysics Data System (ADS)

    Kotko, I.; Lasota, J.-P.

    2012-09-01

    Context. The physical mechanisms driving angular momentum transport in accretion discs are still unknown. Although it is generally accepted that, in hot discs, the turbulence triggered by the magneto-rotational instability is at the origin of the accretion process in Keplerian discs, it has been found that the values of the stress-to-pressure ratio (the α "viscosity" parameter) deduced from observations of outbursting discs are an order of magnitude higher than those obtained in numerical simulations. Aims: We test the conclusion about the observation-deduced value of α using a new set of data and comparing the results with model outbursts. Methods: We analyse a set of observations of dwarf-nova and AM CVn star outbursts and from the measured decay times determine the hot-disc viscosity parameter αh. We determine if and how this method is model dependent. From the dwarf-nova disc instability model we determine an amplitude vs. recurrence-time relation and compare it to the empirical Kukarkin-Parenago relation between the same, but observed, quantities. Results: We found that all methods we tried, including the one based on the amplitude vs. recurrence-time relation, imply αh ~ 0.1-0.2 and exclude values an order of magnitude lower. Conclusions: The serious discrepancy between the observed and the MRI-calculated values of the accretion disc viscosity parameter α is therefore real since there can be no doubt about the validity of the values deduced from observations of disc outbursts.

  5. Genomic instability during reprogramming by nuclear transfer is DNA replication dependent.

    PubMed

    Chia, Gloryn; Agudo, Judith; Treff, Nathan; Sauer, Mark V; Billing, David; Brown, Brian D; Baer, Richard; Egli, Dieter

    2017-04-01

    Somatic cells can be reprogrammed to a pluripotent state by nuclear transfer into oocytes, yet developmental arrest often occurs. While incomplete transcriptional reprogramming is known to cause developmental failure, reprogramming also involves concurrent changes in cell cycle progression and nuclear structure. Here we study cellular reprogramming events in human and mouse nuclear transfer embryos prior to embryonic genome activation. We show that genetic instability marked by frequent chromosome segregation errors and DNA damage arise prior to, and independent of, transcriptional activity. These errors occur following transition through DNA replication and are repaired by BRCA1. In the absence of mitotic nuclear remodelling, DNA replication is delayed and errors are exacerbated in subsequent mitosis. These results demonstrate that independent of gene expression, cell-type-specific features of cell cycle progression constitute a barrier sufficient to prevent the transition from one cell type to another during reprogramming.

  6. Dependence of the electron-cloud instability on the beam energy.

    PubMed

    Rumolo, G; Arduini, G; Métral, E; Shaposhnikova, E; Benedetto, E; Calaga, R; Papotti, G; Salvant, B

    2008-04-11

    The electron cloud (EC) can be formed in the beam pipe of a circular accelerator if the secondary emission yield (SEY) of the inner surface is larger than 1, and it can detrimentally affect the circulating beam. Understanding the underlying physics and defining the scaling laws of this effect is indispensable to steer the upgrade plans of the existing machines and the design of new ones. The single bunch EC instability (ECI) is shown to be strongly affected by the transverse beam size. Transversely, smaller beams going through an electron cloud generate higher electron peak densities and lower the intensity threshold to make the beam unstable. In particular, since higher energy beams have smaller transverse sizes (for equal normalized transverse emittances), the scaling of the ECI threshold with the beam energy turns out to be surprisingly unfavorable.

  7. Emerging ideas: Instability-induced periprosthetic osteolysis is not dependent on the fibrous tissue interface.

    PubMed

    Nam, Denis; Bostrom, Mathias P G; Fahlgren, Anna

    2013-06-01

    Stable initial fixation of a total joint arthroplasty implant is critical to avoid the risk of aseptic loosening and premature clinical failure. With implant motion, a fibrous tissue layer forms at the bone-implant interface, leading to implant migration and periprosthetic osteolysis. At the time of implant revision surgery, proresorptive signaling cytokines are expressed in the periimplant fibrous membrane. However, the exact role of this fibrous tissue in causing periprosthetic osteolysis attributable to instability remains unknown. We propose an alternative mechanism of periprosthetic osteolysis independent of the fibrous tissue layer, where pressurized fluid flow along the bone-implant interface activates mechanosensitive osteocytes in the periprosthetic bone, causing the release of proresorptive cytokines and subsequent osteoclast differentiation and osteolysis. An animal model for instability-induced osteolysis that mimics the periprosthetic bone-implant interface will be used. In this model, a fibrous tissue membrane is allowed to form in the periprosthetic zone, and pressurized fluid flow transmitted through this membrane reliably creates osteolytic lesions in the periprosthetic bone. In this study, half of the rats will have the fibrous tissue present, while the other half will not. We will determine whether the fibrous tissue membrane is essential for the release of proosteoclastic cytokines, leading to osteoclast differentiation and periprosthetic bone loss, by measuring the volume of bone resorption and presence of proresorptive cytokines at the bone-implant interface. We will determine whether the fibrous tissue membrane is crucial for osteoclastogenic signaling in the setting of periimplant osteolysis. In the future, this will allow us to test therapeutic interventions, such as specific cytokine inhibitors or alterations in implant design, which may translate into new, clinically relevant strategies to prevent osteolysis.

  8. Herniated Cervical Disc

    MedlinePlus

    ... center of the disc may start to lose water content, making the disc less effective as a cushion. As a disc deteriorates, the outer layer can also tear. This can allow displacement of the disc's center (called a herniated or ...

  9. The inner cavity of the circumnuclear disc

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  10. Temperature-dependent instability of the cTnI subunit in NIST SRM2921 characterized by tryptic peptide mapping.

    PubMed

    van der Burgt, Yuri E M; Cobbaert, Christa M; Dalebout, Hans; Smit, Nico; Deelder, André M

    2012-08-01

    In this study temperature-dependent instability of the cTnI subunit of the three-protein complex NIST SRM2921 was demonstrated using a mass spectrometric tryptic peptide mapping approach. The results were compared to the cTnI subunit obtained as a protein standard from Calbiochem with identical amino acid sequence. Both the three-protein complex from NIST as well as the cTnI subunit were incubated at elevated temperatures and then evaluated with respect to the primary sequence. The corresponding peptide maps were analyzed using LC-MS/MS. From a Mascot database search in combination with "semiTrypsin" tolerance it was found that two peptide backbone cleavages had occurred in subunit cTnI in NIST SRM2921 material upon incubation at 37°C, namely between amino acids at 148/149 and 194/195. The Calbiochem standard did not show increased levels of "unexpected" peptides in tryptic peptide maps. One of the two peptide backbone cleavages could also be monitored using a "single-step" MALDI-MS approach, i.e. without the need for peptide separation. The amount of degradation appeared rather constant in replicate temperature-instability experiments. However, for accurate quantification internal labelled standards are needed. Copyright © 2012 Elsevier B.V. All rights reserved.

  11. Growth of an ice disk: dependence of critical thickness for disk instability on supercooling of water.

    PubMed

    Yokoyama, Etsuro; Sekerka, Robert F; Furukawa, Yoshinori

    2009-04-09

    The appearance of an asymmetrical pattern that occurs when a disk crystal of ice grows from supercooled water was studied by using an analysis of growth rates for radius and thickness. The growth of the radius is controlled by transport of latent heat and is calculated by solving the diffusion equation for the temperature field surrounding the disk. The growth of the thickness is governed by the generation and lateral motion of steps and is expressed as a power function of the supercooling at the center of a basal face. Symmetry breaking with respect to the basal face of an ice disk crystal is observed when the thickness reaches a critical value; then one basal face becomes larger than the other and the disk loses its cylindrical shape. Subsequently, morphological instability occurs at the edge of the larger basal face of the asymmetrical shape (Shimada, W.; Furukawa, Y. J. Phys. Chem. 1997, B101, 6171-6173). We show that the critical thickness is related to the critical condition for the stable growth of a basal face. A difference of growth rates between two basal faces is a possible mechanism for the appearance of the asymmetrical shape.

  12. Cold exposure promotes atherosclerotic plaque growth and instability via UCP1-dependent lipolysis.

    PubMed

    Dong, Mei; Yang, Xiaoyan; Lim, Sharon; Cao, Ziquan; Honek, Jennifer; Lu, Huixia; Zhang, Cheng; Seki, Takahiro; Hosaka, Kayoko; Wahlberg, Eric; Yang, Jianmin; Zhang, Lei; Länne, Toste; Sun, Baocun; Li, Xuri; Liu, Yizhi; Zhang, Yun; Cao, Yihai

    2013-07-02

    Molecular mechanisms underlying the cold-associated high cardiovascular risk remain unknown. Here, we show that the cold-triggered food-intake-independent lipolysis significantly increased plasma levels of small low-density lipoprotein (LDL) remnants, leading to accelerated development of atherosclerotic lesions in mice. In two genetic mouse knockout models (apolipoprotein E(-/-) [ApoE(-/-)] and LDL receptor(-/-) [Ldlr(-/-)] mice), persistent cold exposure stimulated atherosclerotic plaque growth by increasing lipid deposition. Furthermore, marked increase of inflammatory cells and plaque-associated microvessels were detected in the cold-acclimated ApoE(-/-) and Ldlr(-/-) mice, leading to plaque instability. Deletion of uncoupling protein 1 (UCP1), a key mitochondrial protein involved in thermogenesis in brown adipose tissue (BAT), in the ApoE(-/-) strain completely protected mice from the cold-induced atherosclerotic lesions. Cold acclimation markedly reduced plasma levels of adiponectin, and systemic delivery of adiponectin protected ApoE(-/-) mice from plaque development. These findings provide mechanistic insights on low-temperature-associated cardiovascular risks. Copyright © 2013 Elsevier Inc. All rights reserved.

  13. Amplification of Reynolds number dependent processes by wave distortion. [acoustic instability of liquid propellant rocket engines

    NASA Technical Reports Server (NTRS)

    Ventrice, M. B.; Fang, J. C.; Purdy, K. R.

    1975-01-01

    A system using a hot-wire transducer as an analog of a liquid droplet of propellant was employed to investigate the ingredients of the acoustic instability of liquid-propellant rocket engines. It was assumed that the combustion process was vaporization-limited and that the combustion chamber was acoustically similar to a closed-closed right-circular cylinder. Before studying the hot-wire closed-loop system (the analog system), a microphone closed-loop system, which used the response of a microphone as the source of a linear feedback exciting signal, was investigated to establish the characteristics of self-sustenance of acoustic fields. Self-sustained acoustic fields were found to occur only at resonant frequencies of the chamber. In the hot-wire closed-loop system, the response of hot-wire anemometer was used as the source of the feedback exciting signal. The self-sustained acoustic fields which developed in the system were always found to be harmonically distorted and to have as their fundamental frquency a resonant frequency for which there also existed a second resonant frequency which was approximately twice the fundamental frequency.

  14. Experimental study of initial condition dependence on mixing in Richtmyer-Meshkov instabilities

    SciTech Connect

    Balasubramanian, Sridhar; Prestridge, Katherine P; Orlicz, Gregory C; Balasubramaniam, Balakumar J

    2010-11-18

    Recent work has shown that buoyancy-driven turbulence can be affected at late time by initial conditions, thus presenting an opportunity to predict and design late-time turbulent mixing, with transformative impact on our understanding and prediction of Inertial Confinement Fusion and general fluid mixing processes. In this communication, we report results on the initial condition parameters, amplitude ({delta}) and wavelength ({lambda}) of perturbation, that impact the material mixing and transition to turbulence in shock-driven Richtmyer-Meshkov instability. Experiments were conducted using a stable, membrane-free, heavy gas varicose curtain (air-SF{sub 6}-air) at shock Mach number, Ma = 1.2. The velocity and density field of our initial conditions was quantified using Particle Image Velocimetry (PIV) and Planar-Laser Induced Fluorescence (PLIF) respectively. Quantitative measurements on the temporal and spatial evolution of developing structures after first shock and subsequent re-shock at different times obtained using PLlF aid us in understating the importance of the initial conditions on transition to turbulence and mixing.

  15. FANCD2 limits BLM-dependent telomere instability in the alternative lengthening of telomeres pathway.

    PubMed

    Root, Heather; Larsen, Andrew; Komosa, Martin; Al-Azri, Fakhriya; Li, Ren; Bazett-Jones, David P; Stephen Meyn, M

    2016-08-01

    Fanconi anemia and Bloom syndrome are genomic instability syndromes caused by mutations in proteins that participate in overlapping DNA repair and replication pathways. Here, we show that the monoubiquitinated form of the Fanconi Anemia protein FANCD2 acts in opposition to the BLM DNA helicase to restrain telomere replication and recombination in human cells that utilize the Alternative Lengthening of Telomeres (ALT) pathway. ALT relies on exchanges of telomeric DNA to maintain telomeres, a process that we show FANCD2 suppresses. Depletion of FANCD2 results in a hyper-ALT phenotype, including an increase in extrachromosomal telomeric repeat DNAs, putative recombinational byproducts that we show exist as intertwined complexes forming the nucleic acid component of ALT-associated PML bodies. Increases in telomeric DNA are suppressed by loss of BLM but not RAD51, occur without parallel upregulation of shelterin proteins TRF1 and TRF2, and are associated with increased frequencies of deprotected and fragile telomeres. Inactivation of the FA pathway does not trigger ALT, as FANCD2 depleted telomerase positive cells do not acquire ALT-like phenotypes. We observe frequent fragile telomeres in ALT cells, suggesting that telomere sequences are prone to replication problems. We propose that, in ALT cells, FANCD2 promotes intramolecular resolution of stalled replication forks in telomeric DNA while BLM facilitates their resection and subsequent involvement in the intermolecular exchanges that drive ALT. © The Author 2016. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  16. Sizes of protoplanetary discs after star-disc encounters

    NASA Astrophysics Data System (ADS)

    Breslau, Andreas; Steinhausen, Manuel; Vincke, Kirsten; Pfalzner, Susanne

    2014-05-01

    Most stars do not form in isolation, but as part of a star cluster or association. These young stars are initially surrounded by protoplanetary discs. In these cluster environments tidal interactions with other cluster members can alter the disc properties. Besides the disc frequency, its mass, angular momentum, and energy, the disc's size is particularly prone to being changed by a passing star. So far the change in disc size has only been investigated for a small number of very specific encounters. Several studies investigated the effect of the cluster environment on the sizes of planetary systems like our own solar system, based on a generalisation of information from this limited sample. We performed numerical simulations covering the wide parameter space typical of young star clusters, to test the validity of this approach. Here the sizes of discs after encounters are presented, based on a size definition that is comparable to the one used in observational studies. We find that, except for encounters between equal-mass stars, the usually applied estimates are insufficient. They tend to severely overestimate the remaining disc size. We show that the disc size after an encounter can be described by a relatively simple dependence on the periastron distance and the mass ratio of the encounter partners. This knowledge allows us, for example, to pin down the types of encounter possibly responsible for the structure of today's solar system. Appendix A is available in electronic form at http://www.aanda.org

  17. Sound velocities in highly oriented pyrolytic graphite shocked to 18 GPa: Orientational order dependence and elastic instability

    DOE PAGES

    Lucas, Marcel; Winey, J. M.; Gupta, Y. M.

    2015-12-28

    Previous reports of rapid phase transformation above 18 GPa [Erskine and Nellis, Nature 349, 317 (1991)] and large elastic waves below 18 GPa [Lucas et al., J. Appl. Phys. 114, 093515 (2013)] for shock-compressed ZYB-grade highly-oriented pyrolytic graphite (HOPG), but not for less oriented ZYH-grade HOPG, indicated a link between the orientational order dependence of the HOPG response above and below the phase transformation stress. To gain insight into this link and into the mechanical response of HOPG shocked to peak stresses approaching the phase transformation onset, the compressibility of ZYB- and ZYH-grade HOPG in the shocked state was examinedmore » using front surface impact experiments. Particle velocity histories and sound velocities were measured for peak stresses reaching 18 GPa. Although the locus of the measured peak stress-particle velocity states is indistinguishable for the two grades of HOPG, the measured sound velocities in the peak state reveal significant differences between the two grades. Specifically, 1) The measured sound velocities are somewhat higher for ZYH-grade HOPG, compared to ZYB-grade HOPG. 2) The measured sound velocities for ZYH-grade HOPG increase smoothly with compression, whereas those for ZYB-2 grade HOPG exhibit a significant reduction in the compression dependence from 12 GPa to 17 GPa and an abrupt increase from 17 GPa to 18 GPa. 3) The longitudinal moduli, determined from the measured sound velocities, are smaller than the calculated bulk moduli for ZYB-grade HOPG shocked to peak stresses above 15 GPa, indicating the onset of an elastic instability. The present findings demonstrate that the softening of the longitudinal modulus (or elastic instability) presented here is linked to the large elastic waves and the rapid phase transformation reported previously – all observed only for shocked ZYB-grade HOPG. The elastic instability in shocked ZYB-grade HOPG is likely a precursor to the rapid phase transformation observed

  18. Ion Bernstein instability dependence on the proton-to-electron mass ratio: Linear dispersion theory

    NASA Astrophysics Data System (ADS)

    Min, Kyungguk; Liu, Kaijun

    2016-07-01

    Fast magnetosonic waves, which have as their source ion Bernstein instabilities driven by tenuous ring-like proton velocity distributions, are frequently observed in the inner magnetosphere. One major difficulty in the simulation of these waves is that they are excited in a wide frequency range with discrete harmonic nature and require time-consuming computations. To overcome this difficulty, recent simulation studies assumed a reduced proton-to-electron mass ratio, mp/me, and a reduced light-to-Alfvén speed ratio, c/vA, to reduce the number of unstable modes and, therefore, computational costs. Although these studies argued that the physics of wave-particle interactions would essentially remain the same, detailed investigation of the effect of this reduced system on the excited waves has not been done. In this study, we investigate how the complex frequency, ω = ωr+iγ, of the ion Bernstein modes varies with mp/me for a sufficiently large c/vA (such that ωpe2/Ωe2≡(me/mp)(c/vA)2≫1) using linear dispersion theory assuming two different types of energetic proton velocity distributions, namely, ring and shell. The results show that low- and high-frequency harmonic modes respond differently to the change of mp/me. For the low harmonic modes (i.e., ωr˜Ωp), both ωr/Ωp and γ/Ωp are roughly independent of mp/me, where Ωp is the proton cyclotron frequency. For the high harmonic modes (i.e., Ωp≪ωr≲ωlh, where ωlh is the lower hybrid frequency), γ/ωlh (at fixed ωr/ωlh) stays independent of mp/me when the parallel wave number, k∥, is sufficiently large and becomes inversely proportional to (mp/me)1/4 when k∥ goes to zero. On the other hand, the frequency range of the unstable modes normalized to ωlh remains independent of mp/me, regardless of k∥.

  19. Investigation of negative bias temperature instability dependence on fin width of silicon-on-insulator-fin-based field effect transistors

    SciTech Connect

    Young, Chadwin D. Wang, Zhe; Neugroschel, Arnost; Majumdar, Kausik; Matthews, Ken; Hobbs, Chris

    2015-01-21

    The fin width dependence of negative bias temperature instability (NBTI) of double-gate, fin-based p-type Field Effect Transistors (FinFETs) fabricated on silicon-on-insulator (SOI) wafers was investigated. The NBTI degradation increased as the fin width narrowed. To investigate this phenomenon, simulations of pre-stress conditions were employed to determine any differences in gate oxide field, fin band bending, and electric field profile as a function of the fin width. The simulation results were similar at a given gate stress bias, regardless of the fin width, although the threshold voltage was found to increase with decreasing fin width. Thus, the NBTI fin width dependence could not be explained from the pre-stress conditions. Different physics-based degradation models were evaluated using specific fin-based device structures with different biasing schemes to ascertain an appropriate model that best explains the measured NBTI dependence. A plausible cause is an accumulation of electrons that tunnel from the gate during stress into the floating SOI fin body. As the fin narrows, the sidewall device channel moves in closer proximity to the stored electrons, thereby inducing more band bending at the fin/dielectric interface, resulting in a higher electric field and hole concentration in this region during stress, which leads to more degradation. The data obtained in this work provide direct experimental proof of the effect of electron accumulation on the threshold voltage stability in FinFETs.

  20. Investigation of negative bias temperature instability dependence on fin width of silicon-on-insulator-fin-based field effect transistors

    NASA Astrophysics Data System (ADS)

    Young, Chadwin D.; Neugroschel, Arnost; Majumdar, Kausik; Matthews, Ken; Wang, Zhe; Hobbs, Chris

    2015-01-01

    The fin width dependence of negative bias temperature instability (NBTI) of double-gate, fin-based p-type Field Effect Transistors (FinFETs) fabricated on silicon-on-insulator (SOI) wafers was investigated. The NBTI degradation increased as the fin width narrowed. To investigate this phenomenon, simulations of pre-stress conditions were employed to determine any differences in gate oxide field, fin band bending, and electric field profile as a function of the fin width. The simulation results were similar at a given gate stress bias, regardless of the fin width, although the threshold voltage was found to increase with decreasing fin width. Thus, the NBTI fin width dependence could not be explained from the pre-stress conditions. Different physics-based degradation models were evaluated using specific fin-based device structures with different biasing schemes to ascertain an appropriate model that best explains the measured NBTI dependence. A plausible cause is an accumulation of electrons that tunnel from the gate during stress into the floating SOI fin body. As the fin narrows, the sidewall device channel moves in closer proximity to the stored electrons, thereby inducing more band bending at the fin/dielectric interface, resulting in a higher electric field and hole concentration in this region during stress, which leads to more degradation. The data obtained in this work provide direct experimental proof of the effect of electron accumulation on the threshold voltage stability in FinFETs.

  1. Deoxyinosine triphosphate induces MLH1/PMS2- and p53-dependent cell growth arrest and DNA instability in mammalian cells

    PubMed Central

    Yoneshima, Yasuto; Abolhassani, Nona; Iyama, Teruaki; Sakumi, Kunihiko; Shiomi, Naoko; Mori, Masahiko; Shiomi, Tadahiro; Noda, Tetsuo; Tsuchimoto, Daisuke; Nakabeppu, Yusaku

    2016-01-01

    Deoxyinosine (dI) occurs in DNA either by oxidative deamination of a previously incorporated deoxyadenosine residue or by misincorporation of deoxyinosine triphosphate (dITP) from the nucleotide pool during replication. To exclude dITP from the pool, mammals possess specific hydrolysing enzymes, such as inosine triphosphatase (ITPA). Previous studies have shown that deficiency in ITPA results in cell growth suppression and DNA instability. To explore the mechanisms of these phenotypes, we analysed ITPA-deficient human and mouse cells. We found that both growth suppression and accumulation of single-strand breaks in nuclear DNA of ITPA-deficient cells depended on MLH1/PMS2. The cell growth suppression of ITPA-deficient cells also depended on p53, but not on MPG, ENDOV or MSH2. ITPA deficiency significantly increased the levels of p53 protein and p21 mRNA/protein, a well-known target of p53, in an MLH1-dependent manner. Furthermore, MLH1 may also contribute to cell growth arrest by increasing the basal level of p53 activity. PMID:27618981

  2. Gravitoturbulence in magnetized protostellar discs

    NASA Astrophysics Data System (ADS)

    Riols, A.; Latter, H.

    2016-08-01

    Gravitational instability (GI) features in several aspects of protostellar disc evolution, most notably in angular momentum transport, fragmentation, and the outbursts exemplified by FU Ori and EX Lupi systems. The outer regions of protostellar discs may also be coupled to magnetic fields, which could then modify the development of GI. To understand the basic elements of their interaction, we perform local 2D ideal and resistive magnetohydrodynamics simulations with an imposed toroidal field. In the regime of moderate plasma beta, we find that the system supports a hot gravitoturbulent state, characterized by considerable magnetic energy and stress and a surprisingly large Toomre parameter Q ≳ 10. This result has potential implications for disc structure, vertical thickness, ionization, etc. Our simulations also reveal the existence of long-lived and dense `magnetic islands' or plasmoids. Lastly, we find that the presence of a magnetic field has little impact on the fragmentation criterion of the disc. Though our focus is on protostellar discs, some of our results may be relevant for the outer radii of AGN.

  3. Hydrodynamic ablation of protoplanetary discs via supernovae

    NASA Astrophysics Data System (ADS)

    Close, J. L.; Pittard, J. M.

    2017-07-01

    We present three-dimensional simulations of a protoplanetary disc subject to the effect of a nearby (0.3 pc distant) supernova (SN), using a time-dependent flow from a one-dimensional numerical model of the supernova remnant (SNR), in addition to constant peak ram pressure simulations. Simulations are performed for a variety of disc masses and inclination angles. We find disc mass-loss rates that are typically 10-7-10-6 M⊙ yr-1 (but they peak near 10-5 M⊙ yr-1 during the 'instantaneous' stripping phase) and are sustained for around 200 yr. Inclination angle has little effect on the mass-loss unless the disc is close to edge-on. Inclined discs also strip asymmetrically with the trailing edge ablating more easily. Since the interaction lasts less than one outer rotation period, there is not enough time for the disc to restore its symmetry, leaving the disc asymmetrical after the flow has passed. Of the low-mass discs considered, only the edge-on disc is able to survive interaction with the SNR (with 50 per cent of its initial mass remaining). At the end of the simulations, discs that survive contain fractional masses of SN material up to 5 × 10-6. This is too low to explain the abundance of short-lived radionuclides in the early Solar system, but a larger disc and the inclusion of radiative cooling might allow the disc to capture a higher fraction of SN material.

  4. Analytical, time-dependent mass function and fragmentation rate due to gravitational instability

    NASA Astrophysics Data System (ADS)

    di Fazio, A.

    1986-04-01

    An analytical, theoretical, time-dependent initial mass function is derived for the objects created in the fragmentation of a gravitationally unstable gas protocloud. The mass spectrum depends on the chemical-dynamical-radiative evolution of the protocloud, and it peaks at a mass slightly greater than the minimum Jeans mass attained throughout the evolution. A fragmentation rate mass spectrum is also analytically derived. By using an evolutionary model presented here, it is shown that the fragmentation process implies the existence of several generations of fragments, with different ranges of mass. A protogalactic evolution model, using the new theory, predicts that the first stars are created in the third generation of fragments. These can represent the 'zero-metal' population. Mass functions for various objects are elaborated from observational data. Their shapes are compared among themselves quantitatively. A striking similarity suggests the hypothesis that all the different kinds of astrophysical objects examined were formed by essentially the same process. The theoretical mass functions predicted by the evolutionary models and the fragmentation rate are quantitatively compared with the observations, yielding a remarkably good agreement.

  5. Plasmodium Infection Promotes Genomic Instability and AID Dependent B Cell Lymphoma

    PubMed Central

    Robbiani, Davide F.; Deroubaix, Stephanie; Feldhahn, Niklas; Oliveira, Thiago Y.; Callen, Elsa; Wang, Qiao; Jankovic, Mila; Silva, Israel T.; Rommel, Philipp C.; Bosque, David; Eisenreich, Tom; Nussenzweig, André; Nussenzweig, Michel C.

    2015-01-01

    Summary Chronic infection with Plasmodium falciparum was epidemiologically associated with endemic Burkitt’s lymphoma, a mature B cell cancer characterized by chromosome translocation between the c-myc oncogene and Igh, over 50 years ago. Whether infection promotes B cell lymphoma, and if so by what mechanism remains unknown. To investigate the relationship between parasitic disease and lymphomagenesis we used Plasmodium chabaudi (Pc) to produce chronic malaria infection in mice. Pc induces prolonged expansion of germinal centers (GCs), unique compartments where B cells undergo rapid clonal expansion and express activation-induced cytidine deaminase (AID), a DNA mutator. GC B cells elicited during Pc infection suffer widespread DNA damage leading to chromosome translocations. Although infection does not change the overall rate, it modifies lymphomagenesis to favor mature B cell lymphomas that are AID dependent and show chromosome translocations. Thus, malaria infection favors mature B cell cancers by eliciting protracted AID expression in GC B cells. PMID:26276629

  6. Macroeconomic adjustment in developing countries: instability, short-run growth, and external dependency

    SciTech Connect

    Leff, N.H.; Sato, K.

    1980-05-01

    This paper presents an aggregate model for analyzing macroeconomic adjustment and short-run growth in less-developed countries. The model is built on standard theoretical lines; but an important finding of the paper is that empirically, macroeconomic adjustment in the real sector of some differs from the professional expectations that may be prevalent in more-developed countries. This observation leads us to a reconsideration of the macroeconomics of the developing economies, and particularly of some short-term features that affect the long-run expansion path. The analysis also shows why these economies are often subject to chronic inflation and macroeconmic dependence on foreign-capital inflows. 13 references, 4 tables.

  7. Parametric dependence of density limits in the Tokamak Experiment for Technology Oriented Research (TEXTOR): Comparison of thermal instability theory with experiment

    NASA Astrophysics Data System (ADS)

    Kelly, F. A.; Stacey, W. M.; Rapp, J.

    2001-11-01

    The observed dependence of the TEXTOR [Tokamak Experiment for Technology Oriented Research: E. Hintz, P. Bogen, H. A. Claassen et al., Contributions to High Temperature Plasma Physics, edited by K. H. Spatschek and J. Uhlenbusch (Akademie Verlag, Berlin, 1994), p. 373] density limit on global parameters (I, B, P, etc.) and wall conditioning is compared with the predicted density limit parametric scaling of thermal instability theory. It is necessary first to relate the edge parameters of the thermal instability theory to n¯ and the other global parameters. The observed parametric dependence of the density limit in TEXTOR is generally consistent with the predicted density limit scaling of thermal instability theory. The observed wall conditioning dependence of the density limit can be reconciled with the theory in terms of the radiative emissivity temperature dependence of different impurities in the plasma edge. The thermal instability theory also provides an explanation of why symmetric detachment precedes radiative collapse for most low power shots, while a multifaceted asymmetric radiation from the edge MARFE precedes detachment for most high power shots.

  8. Coupled Marangoni-Benard/Rayleigh-Benard Instability with Temperature Dependent Viscosity

    NASA Technical Reports Server (NTRS)

    Skarda, J. Raymond Lee; Mccaughan, Frances E.

    1994-01-01

    The onset of convection induced by coupled surface tension gradient and buoyancy forces is investigated with temperature dependent viscosity. Both surface tension and viscosity are assumed to vary linearly with temperature. The limiting case, Ma=0, is the buoyancy driven convection problem typically referred to as the Rayleigh-Benard stability problem. The other limiting case, Ra=0, is the surface tension (gradient) driven flow problem referred to as the Marangoni-Benard problem. The equations and boundary conditions obtained from the linear analysis are solved numerically as a generalized eigenvalue problem. Neutral stability curves for different viscosity slopes have been generated for the Marangoni-Benard and Rayleigh-Benard problems. It is shown that the curves can be collapsed to a single curve by appropriately scaling the results for each of the limiting cases. The critical Marangoni number is determined as a function of the slope of the viscosity temperature variation, epsilon, for different values of the Rayleigh number. When the viscosity decreases linearly with temperature, the coupled buoyancy-surface tension problem, including the limiting cases of Ra=0 and Ma=0, is found to be more stable than the constant viscosity case.

  9. Artificial Disc Replacement

    MedlinePlus

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

  10. The Evolution of the single-mode Rayleigh-Taylor instability under the influence of time-dependent accelerations

    NASA Astrophysics Data System (ADS)

    Ramaprabhu, Praveen; Karkhanis, Varad; Banerjee, Rahul; Varshochi, Hilda; Khan, Manoranjan; Lawrie, Andrew; Variable g RT Collaboration

    2015-11-01

    From detailed numerical simulations of the single-mode Rayleigh-Taylor (RT) instability driven by time-varying acceleration histories, we report on several findings of relevance to the performance of Inertial Confinement Fusion capsules. The incompressible, Direct Numerical Simulations (DNS) were performed in two- and three-dimensions, and over a range of density ratios of the fluid combinations (characterized by the Atwood number). We have investigated several acceleration histories, including acceleration profiles g(t) of the general form tn, with n > -2. For the 2D flow, results from numerical simulations are compared with a potential flow model developed and reported as part of this work. When the simulations are extended to three dimensions, bubble and spike growth rates are in agreement with an extension to the drag buoyancy model with modifications for time-dependent acceleration histories. We have come up with simple analytic solutions to the Drag Buoyancy model for variable g flows, and compared the solution with the 2D and 3D DNS results. This work was supported in part by the (U.S.) Department of Energy (DOE) under Contract No. DE-AC52-06NA2-5396.

  11. Higher-Order Modes of Modulation Instability in Bose-Einstein Condensates with a Time-Dependent Three-Dimensional Parabolic Potential

    NASA Astrophysics Data System (ADS)

    Zong, Feng-De; Yan, Yu-Sheng; Shen, Sen-Ting

    2014-10-01

    By the similarity reduction and Darboux transformation, we derive higher-order modes of three-dimensional Bose-Einstein condensate modulation instability in the nonautonomous Gross-Pitaevskii equation and manipulate them by regulating the time-dependent potential and gain. Firstly, by the similarity reduction, the (3+1)-dimensional nonautonomous Gross-Pitaevskii equation reduces to a (1+1)-dimensional standard nonlinear Schrödinger equation with constant coefficients. Then, considering the Akhmediev breather solution as the first-order modulation instability solution of the higher-order modes of Bose-Einstein condensate modulation instability, we achieve the Nth-order (N = 2, 3, 4, and 5) modulation instability solutions by the Darboux transformation. Finally, we verify the stable higher-order modes of Bose-Einstein condensate modulation instability and manipulate them by direct numerical simulation. The obtained results may raise the possibility of related experiments and potential applications in Bose-Einstein condensates and other related fields.

  12. Biomechanics of Disc Degeneration

    PubMed Central

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

    2012-01-01

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

  13. Redundant disc

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

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

  14. A viscosity prescription for a self-gravitating accretion disc

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.; Pringle, J. E.

    1987-01-01

    A model for treating the transfer of angular momentum within a gaseous differentially rotating disc subject to gravitational instability is discussed in terms of an effective kinematic viscosity. It is assumed that even when matter in the disc is subject to self-gravitation, the instability does not necessarily lead directly to condensation of parts of the disc into self-gravitating bodies. Conditions under which the present model permits a similarity solution are discussed, and it is shown that the general solution tends to the similarity solution at large times.

  15. A viscosity prescription for a self-gravitating accretion disc

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.; Pringle, J. E.

    1987-01-01

    A model for treating the transfer of angular momentum within a gaseous differentially rotating disc subject to gravitational instability is discussed in terms of an effective kinematic viscosity. It is assumed that even when matter in the disc is subject to self-gravitation, the instability does not necessarily lead directly to condensation of parts of the disc into self-gravitating bodies. Conditions under which the present model permits a similarity solution are discussed, and it is shown that the general solution tends to the similarity solution at large times.

  16. Close-packing of growing discs

    SciTech Connect

    Bursill, L.A.; Xudong, F. . School of Physics)

    1988-12-01

    Spiral lattices are derived by allowing growing discs to aggregate under a close-packing rule. Both Fibonacci and Lucas numbers of visible spirals arise naturally, dependent only on the choice of growth centre. Both the rate of convergence towards an ideal spiral, and chirality, are determined by the initial placement of the first few discs (initial conditions). Thus the appearance of spiral packings is no more or less mysterious than the appearance of hexagonal packed arrays of equal discs.

  17. Evolution of protoplanetary discs with magnetically driven disc winds

    NASA Astrophysics Data System (ADS)

    Suzuki, Takeru K.; Ogihara, Masahiro; Morbidelli, Alessandro; Crida, Aurélien; Guillot, Tristan

    2016-12-01

    Aims: We investigate the evolution of protoplanetary discs (PPDs) with magnetically driven disc winds and viscous heating. Methods: We considered an initially massive disc with 0.1 M⊙ to track the evolution from the early stage of PPDs. We solved the time evolution of surface density and temperature by taking into account viscous heating and the loss of mass and angular momentum by the disc winds within the framework of a standard α model for accretion discs. Our model parameters, turbulent viscosity, disc wind mass-loss, and disc wind torque, which were adopted from local magnetohydrodynamical simulations and constrained by the global energetics of the gravitational accretion, largely depends on the physical condition of PPDs, particularly on the evolution of the vertical magnetic flux in weakly ionized PPDs. Results: Although there are still uncertainties concerning the evolution of the vertical magnetic flux that remains, the surface densities show a large variety, depending on the combination of these three parameters, some of which are very different from the surface density expected from the standard accretion. When a PPD is in a wind-driven accretion state with the preserved vertical magnetic field, the radial dependence of the surface density can be positive in the inner region <1-10 au. The mass accretion rates are consistent with observations, even in the very low level of magnetohydrodynamical turbulence. Such a positive radial slope of the surface density strongly affects planet formation because it inhibits the inward drift or even causes the outward drift of pebble- to boulder-sized solid bodies, and it also slows down or even reversed the inward type-I migration of protoplanets. Conclusions: The variety of our calculated PPDs should yield a wide variety of exoplanet systems.

  18. Dynamical cooling of galactic discs by molecular cloud collisions - origin of giant clumps in gas-rich galaxy discs

    NASA Astrophysics Data System (ADS)

    Li, Guang-Xing

    2017-10-01

    Different from Milky Way-like galaxies, discs of gas-rich galaxies are clumpy. It is believed that the clumps form because of gravitational instability. However, a necessary condition for gravitational instability to develop is that the disc must dissipate its kinetic energy effectively, this energy dissipation (also called cooling) is not well understood. We propose that collisions (coagulation) between molecular clouds dissipate the kinetic energy of the discs, which leads to a dynamical cooling. The effectiveness of this dynamical cooling is quantified by the dissipation parameter D, which is the ratio between the free-fall time t_ff≈ 1/ √{G ρ _{disc}} and the cooling time determined by the cloud collision process tcool. This ratio is related to the ratio between the mean surface density of the disc Σdisc and the mean surface density of molecular clouds in the disc Σcloud. When D < 1/3 (which roughly corresponds to Σ _{disc} < 1/3 Σ _cloud), cloud collision cooling is inefficient, and fragmentation is suppressed. When D > 1/3 (which roughly corresponds to Σdisc > 1/3Σcloud), cloud-cloud collisions lead to a rapid cooling through which clumps form. On smaller scales, cloud-cloud collisions can drive molecular cloud turbulence. This dynamical cooling process can be taken into account in numerical simulations as a sub-grid model to simulate the global evolution of disc galaxies.

  19. Stellar discs in Aquarius dark matter haloes

    NASA Astrophysics Data System (ADS)

    DeBuhr, Jackson; Ma, Chung-Pei; White, Simon D. M.

    2012-10-01

    We investigate the gravitational interactions between live stellar discs and their dark matter haloes, using Λ cold dark matter haloes similar in mass to that of the Milky Way taken from the Aquarius Project. We introduce the stellar discs by first allowing the haloes to respond to the influence of a growing rigid disc potential from z = 1.3 to 1.0. The rigid potential is then replaced with star particles which evolve self-consistently with the dark matter particles until z = 0.0. Regardless of the initial orientation of the disc, the inner parts of the haloes contract and change from prolate to oblate as the disc grows to its full size. When the disc's normal is initially aligned with the major axis of the halo at z = 1.3, the length of the major axis contracts and becomes the minor axis by z = 1.0. Six out of the eight discs in our main set of simulations form bars, and five of the six bars experience a buckling instability that results in a sudden jump in the vertical stellar velocity dispersion and an accompanying drop in the m = 2 Fourier amplitude of the disc surface density. The bars are not destroyed by the buckling but continue to grow until the present day. Bars are largely absent when the disc mass is reduced by a factor of 2 or more; the relative disc-to-halo mass is therefore a primary factor in bar formation and evolution. A subset of the discs is warped at the outskirts and contains prominent non-coplanar material with a ring-like structure. Many discs reorient by large angles between z = 1 and 0, following a coherent reorientation of their inner haloes. Larger reorientations produce more strongly warped discs, suggesting a tight link between the two phenomena. The origins of bars and warps appear independent: some discs with strong bars show little disturbances at the outskirts, while the discs with the weakest bars show severe warps.

  20. Variables affecting disc size in the lumbar spine of rabbits: anesthesia, paralysis, and disc injury.

    PubMed

    Neufeld, J H; Machado, T; Margolin, L

    1991-01-01

    Methods have been developed that permit repetitive radiographic measurement of the lumbar intervertebral disc space in a rostral-caudal direction (width) in the anesthetized laboratory rabbit. Using isolated control discs and injured discs in which narrowing has been induced for chronic and acute periods, the widths of the lumbar intervertebral disc spaces determined ratio-graphically correlate with widths determined histologically (p less than 0.000, r = 0.75). Both an increase (widening) and a decrease (narrowing) in disc width were observed using radiography after different experimental treatments. Anesthesia and lower-body paralysis (an experimentally induced inability to bear weight on and to perceive a pinch stimulus in hind limbs) caused widening of the discs: anesthesia causing a general widening throughout the lumbar spine and lower-body paralysis causing a specific widening low in the lumbar spine. Both disc injection and piercing the disc with needles to recover nucleus pulposus material caused narrowing of the discs. Acridine-orange injection induced a narrowing accompanied by osteophytosis. Experimentally induced narrowing at L4-5 (the result of injury to the disc) resulted in narrowing also at L2-3. These findings are consistent with the hypothesis that in vivo disc-width size in the young rabbit depends on both the quantity of nucleus pulposus material and the force-generating activities of the adjacent spinal muscles, and that disc injury at one level stimulates narrowing at other levels.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  2. Particle rings and astrophysical accretion discs

    SciTech Connect

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

    2016-03-25

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

  3. Dependence of Gait Deviation on Weight-Bearing Asymmetry and Postural Instability in Children with Unilateral Cerebral Palsy

    PubMed Central

    Domagalska-Szopa, Małgorzata; Szopa, Andrzej; Czamara, Andrzej

    2016-01-01

    Postural control deficits have been suggested to be a major component of gait disorders in children with cerebral palsy. The purpose of this study was to investigate the relationship between postural stability and treadmill walking, in children with unilateral cerebral palsy, by defining dependence between the posturographic weight-bearing distribution and center of pressure (CoP) sway during quiet standing with Gillette Gait Index and the 16 distinct gait parameters that composed the Gillette Gait Index. Forty-five children with unilateral cerebral palsy from 7–12 years of age were included in this study. A posturographic procedure and 3-dimensional instrumented gait analysis was developed. In general, across the entire tested group, the significant correlations concerned only the asymmetry of the weight bearing and a few of the distinct gait parameters that compose the Gillette Gait Index; moreover, correlation coefficients were low. The division of subjects into two clinical subgroups: children that exhibited a tendency to overload (1) and to underload (2) the affected body side, modified the results of the explored relationships. Our findings revealed that the difficulties experienced by children with hemiplegia while controlled in a standing position result from tendency to excessively or insufficiently load the affected lower limbs, and thus establishes a direct relationship with inadequate affected peak ankle DF in both stance and swing gait phases. Given the presented relationship between postural instability and deviation of the particular gait parameters in children with unilateral cerebral palsy, a follow-up study will be needed to determine the therapeutic approaches that will be most effective in promoting increased improvement in gait pattern, as well as the static and dynamic balance in standing. PMID:27788247

  4. Evolution of the single-mode Rayleigh-Taylor instability under the influence of time-dependent accelerations.

    PubMed

    Ramaprabhu, P; Karkhanis, V; Banerjee, R; Varshochi, H; Khan, M; Lawrie, A G W

    2016-01-01

    From nonlinear models and direct numerical simulations we report on several findings of relevance to the single-mode Rayleigh-Taylor (RT) instability driven by time-varying acceleration histories. The incompressible, direct numerical simulations (DNSs) were performed in two (2D) and three dimensions (3D), and at a range of density ratios of the fluid combinations (characterized by the Atwood number). We investigated several acceleration histories, including acceleration profiles of the general form g(t)∼t^{n}, with n≥0 and acceleration histories reminiscent of the linear electric motor experiments. For the 2D flow, results from numerical simulations compare well with a 2D potential flow model and solutions to a drag-buoyancy model reported as part of this work. When the simulations are extended to three dimensions, bubble and spike growth rates are in agreement with the so-called level 2 and level 3 models of Mikaelian [K. O. Mikaelian, Phys. Rev. E 79, 065303(R) (2009)10.1103/PhysRevE.79.065303], and with corresponding 3D drag-buoyancy model solutions derived in this article. Our generalization of the RT problem to study variable g(t) affords us the opportunity to investigate the appropriate scaling for bubble and spike amplitudes under these conditions. We consider two candidates, the displacement Z and width s^{2}, but find the appropriate scaling is dependent on the density ratios between the fluids-at low density ratios, bubble and spike amplitudes are explained by both s^{2} and Z, while at large density differences the displacement collapses the spike data. Finally, for all the acceleration profiles studied here, spikes enter a free-fall regime at lower Atwood numbers than predicted by all the models.

  5. Evolution of the single-mode Rayleigh-Taylor instability under the influence of time-dependent accelerations

    NASA Astrophysics Data System (ADS)

    Ramaprabhu, P.; Karkhanis, V.; Banerjee, R.; Varshochi, H.; Khan, M.; Lawrie, A. G. W.

    2016-01-01

    From nonlinear models and direct numerical simulations we report on several findings of relevance to the single-mode Rayleigh-Taylor (RT) instability driven by time-varying acceleration histories. The incompressible, direct numerical simulations (DNSs) were performed in two (2D) and three dimensions (3D), and at a range of density ratios of the fluid combinations (characterized by the Atwood number). We investigated several acceleration histories, including acceleration profiles of the general form g (t ) ˜tn , with n ≥0 and acceleration histories reminiscent of the linear electric motor experiments. For the 2D flow, results from numerical simulations compare well with a 2D potential flow model and solutions to a drag-buoyancy model reported as part of this work. When the simulations are extended to three dimensions, bubble and spike growth rates are in agreement with the so-called level 2 and level 3 models of Mikaelian [K. O. Mikaelian, Phys. Rev. E 79, 065303(R) (2009), 10.1103/PhysRevE.79.065303], and with corresponding 3D drag-buoyancy model solutions derived in this article. Our generalization of the RT problem to study variable g (t ) affords us the opportunity to investigate the appropriate scaling for bubble and spike amplitudes under these conditions. We consider two candidates, the displacement Z and width s2, but find the appropriate scaling is dependent on the density ratios between the fluids—at low density ratios, bubble and spike amplitudes are explained by both s2 and Z , while at large density differences the displacement collapses the spike data. Finally, for all the acceleration profiles studied here, spikes enter a free-fall regime at lower Atwood numbers than predicted by all the models.

  6. Stellar irradiated discs and implications on migration of embedded planets. III. Viscosity transitions

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Morbidelli, Alessandro; Lega, Elena; Kretke, Katherine; Crida, Aurélien

    2014-10-01

    Context. The migration strength and direction of embedded low-mass planets depends on the disc structure. In discs with an efficient radiative transport, the migration can be directed outwards for planets with more than 3-5 Earth masses. This is due to the entropy-driven corotation torque, a process that extends the lifetimes of growing planetary embryos. However, smaller mass planets are still migrating inwards and might be lost to the central star. Aims: We investigate the influence on the disc structure caused by a jump in the α parameter of the viscosity to model a dead-zone structure in the disc. We focus on Ṁ discs, which have a constant net mass flux. Using the resulting disc structure, we investigate the consequences for the formation of planetesimals and determine the regions of outward migration for proto-planets. Methods: We performed numerical hydrosimulations of Ṁ discs in the r - z-plane. We used the explicit/implicit hydrodynamical code FARGOCA that includes a full tensor viscosity and stellar irradiation as well as a two-temperature solver that includes radiation transport in the flux-limited diffusion approximation. The migration of embedded planets was studied by using torque formulae. Results: Viscosity transitions inside the disc create transitions in density that stop inward migration for small planets through the so-called "planet trap" mechanism. This mechanism also works for planets down to MP > 0.5 MEarth, while in radiative discs with no viscosity transition the lowest mass with which inward migration can be avoided is 3-5 Earth masses. Additionally, the viscosity transitions change the pressure gradient in the disc, which facilitates planetesimal formation via the streaming instability. However, a very steep transition in viscosity is needed to achieve in a pressure bump in the disc. Conclusions: The transition in viscosity facilitates planetesimal formation and can stop the migration of small-mass planets (MP > 0.5 MEarth), but

  7. New constraints on turbulent transport in accretion discs

    NASA Astrophysics Data System (ADS)

    Hubbard, A.; Blackman, E. G.

    2009-09-01

    Microphysical viscosity is too small to produce observed proto-planetary accretion disc lifetimes. Turbulent transport, in which turbulent motion takes the place of thermal motion, can provide the correct order-of-magnitude accretion rates for reasonable surface densities, though the source of such turbulence remains a matter of discussion. Here, we consider, independent of the source of turbulence, the minimal properties that turbulent motion must possess in order to adequately transport both angular momentum and mass in accretion discs. We find that the resulting angular momentum transport coefficient depends on the turbulent time scale and angular distribution, not only on the product of the turbulent length and velocity scales. More importantly, we also find that the required energy conversion efficiency is prohibitive if angular momentum transport results purely from fluid turbulence supplied by accretion energy and therefore that turbulent fluid motion mediated accretion must be powered by an outside source. Even in the case that the accretion mechanism is not a turbulent viscosity, as can be the case for a Magneto-Rotational Instability (MRI) disc, numerical simulations suggest that energy conservation is a significant constraint even on accretion driving processes such as the MRI.

  8. Missense mutation in DISC1 C-terminal coiled-coil has GSK3β signaling and sex-dependent behavioral effects in mice.

    PubMed

    Dachtler, James; Elliott, Christina; Rodgers, R John; Baillie, George S; Clapcote, Steven J

    2016-01-05

    Disrupted-in-Schizophrenia 1 (DISC1) is a risk factor for schizophrenia and affective disorders. The full-length DISC1 protein consists of an N-terminal 'head' domain and a C-terminal tail domain that contains several predicted coiled-coils, structural motifs involved in protein-protein interactions. To probe the in vivo effects of missense mutation of DISC1's C-terminal tail, we tested mice carrying mutation D453G within a predicted α-helical coiled-coil region. We report that, relative to wild-type littermates, female DISC1(D453G) mice exhibited novelty-induced hyperlocomotion, an anxiogenic profile in the elevated plus-maze and open field tests, and reduced social exploration of unfamiliar mice. Male DISC1(D453G) mice displayed a deficit in passive avoidance, while neither males nor females exhibited any impairment in startle reactivity or prepulse inhibition. Whole brain homogenates showed normal levels of DISC1 protein, but decreased binding of DISC1 to GSK3β, decreased phospho-inhibition of GSK3β at serine 9, and decreased levels of β-catenin in DISC1(D453G) mice of either sex. Interrupted GSK3β signaling may thus be part of the mechanism underlying the behavioral phenotype associated with D453G, in common with the previously described N-terminal domain mutations Q31L and L100P in mice, and the schizophrenia risk-conferring variant R264Q in humans.

  9. Cell therapy for the degenerating intervertebral disc.

    PubMed

    Tong, Wei; Lu, Zhouyu; Qin, Ling; Mauck, Robert L; Smith, Harvey E; Smith, Lachlan J; Malhotra, Neil R; Heyworth, Martin F; Caldera, Franklin; Enomoto-Iwamoto, Motomi; Zhang, Yejia

    2017-03-01

    Spinal conditions related to intervertebral disc (IVD) degeneration cost billions of dollars in the US annually. Despite the prevalence and soaring cost, there is no specific treatment that restores the physiological function of the diseased IVD. Thus, it is vital to develop new treatment strategies to repair the degenerating IVD. Persons with IVD degeneration without back pain or radicular leg pain often do not require any intervention. Only patients with severe back pain related to the IVD degeneration or biomechanical instability are likely candidates for cell therapy. The IVD progressively degenerates with age in humans, and strategies to repair the IVD depend on the stage of degeneration. Cell therapy and cell-based gene therapy aim to address moderate disc degeneration; advanced stage disease may require surgery. Studies involving autologous, allogeneic, and xenogeneic cells have all shown good survival of these cells in the IVD, confirming that the disc niche is an immunologically privileged site, permitting long-term survival of transplanted cells. All of the animal studies reviewed here reported some improvement in disc structure, and 2 studies showed attenuation of local inflammation. Among the 50 studies reviewed, 25 used some type of scaffold, and cell leakage is a consistently noted problem, though some studies showed reduced cell leakage. Hydrogel scaffolds may prevent cell leakage and provide biomechanical support until cells can become established matrix producers. However, these gels need to be optimized to prevent this leakage. Many animal models have been leveraged in this research space. Rabbit is the most frequently used model (28 of 50), followed by rat, pig, and dog. Sheep and goat IVDs resemble those of humans in size and in the absence of notochordal cells. Despite this advantage, there were only 2 sheep and 1 goat studies of 50 studies in this cohort. It is also unclear if a study in large animals is needed before clinical trials since

  10. TP53-dependent chromosome instability is associated with transient reductions in telomere length in immortal telomerase-positive cell lines

    NASA Technical Reports Server (NTRS)

    Schwartz, J. L.; Jordan, R.; Liber, H.; Murnane, J. P.; Evans, H. H.

    2001-01-01

    Telomere shortening in telomerase-negative somatic cells leads to the activation of the TP53 protein and the elimination of potentially unstable cells. We examined the effect of TP53 gene expression on both telomere metabolism and chromosome stability in immortal, telomerase-positive cell lines. Telomere length, telomerase activity, and chromosome instability were measured in multiple clones isolated from three related human B-lymphoblast cell lines that vary in TP53 expression; TK6 cells express wild-type TP53, WTK1 cells overexpress a mutant form of TP53, and NH32 cells express no TP53 protein. Clonal variations in both telomere length and chromosome stability were observed, and shorter telomeres were associated with higher levels of chromosome instability. The shortest telomeres were found in WTK1- and NH32-derived cells, and these cells had 5- to 10-fold higher levels of chromosome instability. The primary marker of instability was the presence of dicentric chromosomes. Aneuploidy and other stable chromosome alterations were also found in clones showing high levels of dicentrics. Polyploidy was found only in WTK1-derived cells. Both telomere length and chromosome instability fluctuated in the different cell populations with time in culture, presumably as unstable cells and cells with short telomeres were eliminated from the growing population. Our results suggest that transient reductions in telomere lengths may be common in immortal cell lines and that these alterations in telomere metabolism can have a profound effect on chromosome stability. Copyright 2000 Wiley-Liss, Inc.

  11. TP53-dependent chromosome instability is associated with transient reductions in telomere length in immortal telomerase-positive cell lines

    NASA Technical Reports Server (NTRS)

    Schwartz, J. L.; Jordan, R.; Liber, H.; Murnane, J. P.; Evans, H. H.

    2001-01-01

    Telomere shortening in telomerase-negative somatic cells leads to the activation of the TP53 protein and the elimination of potentially unstable cells. We examined the effect of TP53 gene expression on both telomere metabolism and chromosome stability in immortal, telomerase-positive cell lines. Telomere length, telomerase activity, and chromosome instability were measured in multiple clones isolated from three related human B-lymphoblast cell lines that vary in TP53 expression; TK6 cells express wild-type TP53, WTK1 cells overexpress a mutant form of TP53, and NH32 cells express no TP53 protein. Clonal variations in both telomere length and chromosome stability were observed, and shorter telomeres were associated with higher levels of chromosome instability. The shortest telomeres were found in WTK1- and NH32-derived cells, and these cells had 5- to 10-fold higher levels of chromosome instability. The primary marker of instability was the presence of dicentric chromosomes. Aneuploidy and other stable chromosome alterations were also found in clones showing high levels of dicentrics. Polyploidy was found only in WTK1-derived cells. Both telomere length and chromosome instability fluctuated in the different cell populations with time in culture, presumably as unstable cells and cells with short telomeres were eliminated from the growing population. Our results suggest that transient reductions in telomere lengths may be common in immortal cell lines and that these alterations in telomere metabolism can have a profound effect on chromosome stability. Copyright 2000 Wiley-Liss, Inc.

  12. Magnetic field dragging in accretion discs

    NASA Astrophysics Data System (ADS)

    de Guiran, R.; Ferreira, J.

    2010-12-01

    Accretion discs are composed of ionized gas in motion around a central object. Sometimes, the disc is the source of powerful bipolar jets along its rotation axis. Theoretical models invoke the existence of a bipolar magnetic field crossing the disc and require two conditions to produce powerful jets: field lines need to be bent enough at the disc surface and the magnetic field needs to be close to equipartition. The work of Petrucci et al (2008) on the variability of X-ray binaries supposes that transitions between pure accretion phases and accretion-ejection phases are due to some variations of the disc magnetization. This rises the problem of the magnetic field dragging in accretion discs. We revisit the method developed by Lubow et al (1994) by including momentum and mass conservation equations in a time-dependent 1D MHD code.

  13. Time dependence of the laser-induced femtosecond lattice instability of Si and GaAs: Role of longitudinal optical distortions

    NASA Astrophysics Data System (ADS)

    Stampfli, P.; Bennemann, K. H.

    1994-03-01

    We extend our previous analysis of the ultrafast laser-induced instability of the diamond structure of semiconductors by including longitudinal optical-phonon distortions in addition to the instability of the transverse acoustic phonons. Generally, longitudinal optical distortions enhance the instability of the transverse acoustic phonons, increasing the kinetic energy of the atoms and the final lattice temperature. These phonons make a transition to a centrosymmetric structure of GaAs with metallic properties possible. We present results for the time dependence of the instability of Si for the case where 15% of the valence electrons have been excited into the conduction band. Thus, already 100 fsec after the excitation of the plasma the atoms are displaced about 1 Å from their equilibrium position and their kinetic energy has increased to approximately 0.4 eV. Collisions between the atoms then lead to a rapid melting of the crystal. These results are in good agreement with recent experiments performed on Si and GaAs.

  14. Dancing Discs: Bending and Twisting of Soft Materials by Anisotropic Swelling

    NASA Astrophysics Data System (ADS)

    Holmes, Douglas; Roché, Matthieu; Sinha, Tarun; Stone, Howard

    2011-03-01

    Soft materials, e.g. biological tissues and gels, undergo morphological changes, motion, and instabilities when subjected to external stimuli. Tissues can exhibit residual internal stresses induced by growth, and generate elastic deformations to move in response to light or touch, curl articular cartilage, aid in seed dispersal, and actuate hygromorphs, such as pine cones. Understanding the dynamics of such osmotically driven movements, in the influence of geometry and boundary conditions, is crucial to the controlled deformation of soft materials. We examine how thin elastic plates undergo rapid bending and buckling instabilities after anisotropic exposure to a favorable solvent that swells the network. An unconstrained beam bends along its length, while a circular disc bends and buckles with multiple curvatures. In the case of a disc, a large-amplitude transverse travelling wave rotates azimuthally around the disc. Theoretical interpretations inspired by the complementary thermal expansion problem of transient shape changes triggered by time-dependent heating are presented and allow collapse of time-dependent data on universal curves. Understanding the dynamics of strain-driven shape changes provides new insight into natural systems and control of advanced functional materials.

  15. Genomic instability induced in distant progeny of bystander cells depends on the connexins expressed in the irradiated cells.

    PubMed

    de Toledo, Sonia M; Buonanno, Manuela; Harris, Andrew L; Azzam, Edouard I

    2017-06-15

    To examine the time window during which intercellular signaling though gap junctions mediates non-targeted (bystander) effects induced by moderate doses of ionizing radiation; and to investigate the impact of gap junction communication on genomic instability in distant progeny of bystander cells. A layered cell culture system was developed to investigate the propagation of harmful effects from irradiated normal or tumor cells that express specific connexins to contiguous bystander normal human fibroblasts. Irradiated cells were exposed to moderate mean absorbed doses from 3.7 MeV α particle, 1000 MeV/u iron ions, 600 MeV/u silicon ions, or (137)Cs γ rays. Following 5 h of co-culture, pure populations of bystander cells, unexposed to secondary radiation, were isolated and DNA damage and oxidative stress was assessed in them and in their distant progeny (20-25 population doublings). Increased frequency of micronucleus formation and enhanced oxidative changes were observed in bystander cells co-cultured with confluent cells exposed to either sparsely ionizing ((137)Cs γ rays) or densely ionizing (α particles, energetic iron or silicon ions) radiations. The irradiated cells propagated signals leading to biological changes in bystander cells within 1 h of irradiation, and the effect required cellular coupling by gap junctions. Notably, the distant progeny of isolated bystander cells also exhibited increased levels of spontaneous micronuclei. This effect was dependent on the type of junctional channels that coupled the irradiated donor cells with the bystander cells. Previous work showed that gap junctions composed of connexin26 (Cx26) or connexin43 (Cx43) mediate toxic bystander effects within 5 h of co-culture, whereas gap junctions composed of connexin32 (Cx32) mediate protective effects. In contrast, the long-term progeny of bystander cells expressing Cx26 or Cx43 did not display elevated DNA damage, whereas those coupled by Cx32 had enhanced DNA

  16. Time-dependent models of radiatively driven stellar winds. I - Nonlinear evolution of instabilities for a pure absorption model

    NASA Technical Reports Server (NTRS)

    Owocki, Stanley P.; Castor, John I.; Rybicki, George B.

    1988-01-01

    Numerical radiation-hydrodynamics simulations of the nonlinear evolution of instabilities in radiatively driven stellar winds have been performed. The results show a strong tendency for the unstable flow to form rather sharp rarefactions in which the highest speed material has very low density. The qualitative features of the model agree well with the reqirements of displaced narrow absorption components in UV lines.

  17. Linewidth enhancement factor dependence of the instability in semiconductor lasers with delayed feedback and its influence on the analyses

    NASA Astrophysics Data System (ADS)

    Wada, Kenji; Umeda, Tokuo; Cho, Yoshio

    1994-06-01

    The instability enhancement due to the linewidth enhancement factor (α-parameter) in semiconductor lasers with delayed feedback on the regime IV are explained in terms of the laser emission suppression caused by the feedback field using the phasor representation. The discrepancy of the unstable condition due to the adiabatic-following approximation (AFA) is also examined.

  18. Accretion disc viscosity: a limit on the anisotropy

    NASA Astrophysics Data System (ADS)

    Nixon, Chris

    2015-07-01

    Observations of warped discs can give insight into the nature of angular momentum transport in accretion discs. Only a few objects are known to show strong periodicity on long time-scales, but when such periodicity is present it is often attributed to precession of the accretion disc. The X-ray binary Hercules X-1/HZ Herculis (Her X-1) is one of the best examples of such periodicity and has been linked to disc precession since it was first observed. By using the current best-fitting models to Her X-1, which invoke precession driven by radiation warping, I place a constraint on the effective viscosities that act in a warped disc. These effective viscosities almost certainly arise due to turbulence induced by the magnetorotational instability. The constraints derived here are in agreement with analytical and numerical investigations into the nature of magnetohydrodynamic disc turbulence, but at odds with some recent global simulations.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  20. Age-, tissue- and length-dependent bidirectional somatic CAG•CTG repeat instability in an allelic series of R6/2 Huntington disease mice.

    PubMed

    Larson, Eloise; Fyfe, Ian; Morton, A Jennifer; Monckton, Darren G

    2015-04-01

    The expansion of simple sequence CAG•CTG repeats is associated with a number of inherited disorders including Huntington disease (HD), myotonic dystrophy type 1 and several of the spinocerebellar ataxias. Inherited disease-associated alleles usually exceed 40 repeats and may be in excess of 1,000 repeats in some disorders. Inherited allele length is inversely proportional to age at onset, and frequent germline expansions account for the striking anticipation observed in affected families. Expanded disease associated alleles are also somatically unstable via a pathway that is age dependent and tissue specific, and also appears to be expansion biased. Somatic expansions are thought to contribute toward both tissue specificity and disease progression. Here we have examined the somatic mutational dynamics in brain and peripheral tissues from an allelic series of R6/2 HD transgenic mice inheriting from 52 to >700 CAG repeats. We found age-dependent, tissue-specific somatic instability, with particularly large expansions observed in the striatum and cortex. We also found a positive increase in somatic instability with increasing allele length. Surprisingly, however, the degree of somatic variation did not increase in a linear fashion, but leveled off with increasing allele length. Most unexpectedly, the almost exclusive bias toward the accumulation of expansions observed in mice inheriting smaller alleles was lost, and a high frequency of large somatic contractions was observed in mice inheriting very large alleles (>500 repeats). These data highlight the bidirectional nature of CAG•CTG repeat instability and the subtle balance that exists between expansion and contraction in vivo. Defining the dynamics and tissue specificity of expansion and contraction is important for understanding the role of genetic instability in pathophysiology and in particular the development of novel therapies based on suppressing expansions and/or promoting contractions.

  1. Effects of disc midplane evolution on CO snowline location

    NASA Astrophysics Data System (ADS)

    Panić, O.; Min, M.

    2017-01-01

    Temperature changes in the planet forming disc midplanes carry important physico-chemical consequences, such as the effect on the locations of the condensation fronts of molecules - the snowlines. Snowlines impose major chemical gradients and possibly foster grain growth. The aim of this paper is to understand how disc midplane temperature changes with gas and dust evolution, and identify trends that may influence planet formation or allow to constrain disc evolution observationally. We calculate disc temperature, hydrostatic equilibrium and dust settling in a mutually consistent way from a grid of disc models at different stages of gas loss, grain growth and hole opening. We find that the CO snowline location depends very strongly on disc properties. The CO snowline location migrates closer to the star for increasing degrees of gas dispersal and dust growth. Around a typical A type star, the snowline can be anywhere between several tens and a few hundred au, depending on the disc properties such as gas mass and grain size. In fact, gas loss is as efficient as dust evolution in settling discs, and flat discs may be gas-poor counterparts of flared discs. Our results, in the context of different pre-main sequence evolution of the luminosity in low- and intermediate-mass stars suggests very different thermal (and hence chemical) histories in these two types of discs. Discs of T Tauri stars settle and cool down while discs of Herbig Ae stars may remain rather warm throughout the pre-main sequence.

  2. Genetic instability is prevented by Mrc1-dependent spatio-temporal separation of replicative and repair activities of homologous recombination

    PubMed Central

    Prado, Félix

    2014-01-01

    Homologous recombination (HR) is required to protect and restart stressed replication forks. Paradoxically, the Mrc1 branch of the S phase checkpoints, which is activated by replicative stress, prevents HR repair at breaks and arrested forks. Indeed, the mechanisms underlying HR can threaten genome integrity if not properly regulated. Thus, understanding how cells avoid genetic instability associated with replicative stress, a hallmark of cancer, is still a challenge. Here I discuss recent results that support a model by which HR responds to replication stress through replicative and repair activities that operate at different stages of the cell cycle (S and G2, respectively) and in distinct subnuclear structures. Remarkably, the replication checkpoint appears to control this scenario by inhibiting the assembly of HR repair centers at stressed forks during S phase, thereby avoiding genetic instability. PMID:24615940

  3. Dust dynamics in 2D gravito-turbulent discs

    NASA Astrophysics Data System (ADS)

    Shi, Ji-Ming; Zhu, Zhaohuan; Stone, James M.; Chiang, Eugene

    2016-06-01

    The dynamics of solid bodies in protoplanetary discs are subject to the properties of any underlying gas turbulence. Turbulence driven by disc self-gravity shows features distinct from those driven by the magnetorotational instability (MRI). We study the dynamics of solids in gravito-turbulent discs with two-dimensional (in the disc plane), hybrid (particle and gas) simulations. Gravito-turbulent discs can exhibit stronger gravitational stirring than MRI-active discs, resulting in greater radial diffusion and larger eccentricities and relative speeds for large particles (those with dimensionless stopping times tstopΩ > 1, where Ω is the orbital frequency). The agglomeration of large particles into planetesimals by pairwise collisions is therefore disfavoured in gravito-turbulent discs. However, the relative speeds of intermediate-size particles (tstopΩ ˜ 1) are significantly reduced as such particles are collected by gas drag and gas gravity into coherent filament-like structures with densities high enough to trigger gravitational collapse. First-generation planetesimals may form via gravitational instability of dust in marginally gravitationally unstable gas discs.

  4. Turbine disc sealing assembly

    DOEpatents

    Diakunchak, Ihor S.

    2013-03-05

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

  5. Optic disc abnormalities - diagnosis, evolution and influence on visual acuity

    PubMed Central

    Cekić, Sonja; Stanković-Babić, Gordana; Višnjić, Zlatica; Jovanović, Ivan; Risimić, Dijana

    2010-01-01

    Congenital abnormalities of the optic disc are not so rare. The etiology for the most of them is unknown. Visual acuity of affected eye may be minimally or severely affected, depending on the extent of lesion. All of these conditions can be unilateral or bilateral. Chíldren who have unilateral optic disc abnormalities generally present during the preschool years with sensory esotropia. Visual acuity may be unaffected like in optic disc pit, optic disc drusen, fibre medullares, ect. However, during the evolution they may cause a decrease in visual acuity like serous retinal detachment in optic disc pit, atrophy or subretinal neovascularisation in optic disc drusen. Some of them like fibre medullares needs only a good diagnose and they do not have any evolution. Fluorescein angiography and ultrasonography may be crucial diagnostic procedures to discover some of them, like optic disc drusen. Optic disc abnormalities may be associated with other congenital disorders of the eye and often central nervous system malformations. Secondary they may be associated retinal detachment, retinochisis, macular edema, choroid neovascularisation and lipid exudation. Some of these conditions may be found on routine ophthalmologic exam such as optic disc drusen and fibre medullares and often are diagnostically problem. The aim of our study was to present some of our cases with different optic disc abnormalities such as fibre medullares, optic disc coloboma, hypoplasio disci, optic disc drusen and optic disc pit. PMID:20507293

  6. Migration and kinematics in growing disc galaxies with thin and thick discs

    NASA Astrophysics Data System (ADS)

    Aumer, Michael; Binney, James; Schönrich, Ralph

    2017-09-01

    We analyse disc heating and radial migration in N-body models of growing disc galaxies with thick and thin discs. Similar to thin-disc-only models, galaxies with appropriate non-axisymmetric structures reproduce observational constraints on radial disc heating in and migration to the Solar Neighbourhood (Snhd). The presence of thick discs can suppress non-axisymmetries and thus higher baryonic-to-dark matter fractions are required than in models that only have a thin disc. Models that are baryon dominated to roughly the Solar radius R0 are favoured, in agreement with data for the Milky Way. For inside-out growing discs, today's thick-disc stars at R0 are dominated by outwards migrators. Whether outwards migrators are vertically hotter than non-migrators depends on the radial gradient of the thick-disc vertical velocity dispersion. There is an effective upper boundary in angular momentum that thick-disc stars born in the centre of a galaxy can reach by migration, which explains the fading of the high [α/Fe] sequence outside R0. Our models compare well to Snhd kinematics from Radial Velocity Survey and Tycho-Gaia Astrometric Solution data. For such comparisons, it is important to take into account the azimuthal variation of kinematics at R ∼ R0 and biases from survey selection functions. The vertical heating of thin-disc stars by giant molecular clouds is only mildly affected by the presence of thick discs. Our models predict higher vertical velocity dispersions for the oldest stars than found in the Snhd age velocity dispersion relation, possibly because of measurement uncertainties or an underestimation of the number of old cold stars in our models.

  7. [Clinical application of percutaneous laser disc decompression in the treatment of cervical disc herniation].

    PubMed

    Li, Kangren; Qin, Hui; Chen, Jian

    2007-05-01

    To evaluate the clinical effect of percutaneous laser disc decompression (PLDD) in the treatment of cervical disc herniation. From March 2003 to December 2005, 47 patients with cervical disc herniation (96 cervical disc) were treated with PLDD. There were 25 males and 22 females with an average age of 56 years, ranging from 37 to 72 years. The lesion were located at the levels of C3,4 in 20 discs, C4,5 in 27 discs, C5,6 in 31 discs, C6,7 in 18 discs. The laser fiber was introduced into the center of the herniated disc space by percutaneous puncture from anterior neck surface under fluoroscopic guidance. Laser reduced the intra-disc pressure through the vaporization of disc nucleu. The adopted laser was semi-conducted with a wavelength of 810 nm. Each laser output power was 15 W with 1 s emission and 2 s interval. The total laser output power was decided depending on the degenerative degree of the disc and the reactive process of heat, ranging from 300 to 1 000 J. Of 47 patients, 42 were followed up for 3 to 31 months (mean 13 months). The clinical evaluation was classified as excellent in 18 cases (42.9%), good in 14 cases (33.3%), fair in 6 cases (14.3%) and poor in 4 cases (9.5%). The general response rate was 90.5%. The excellent and good rate was 76.2%. No complications occurred. PLDD can relieve the symptoms and signs of patients suffering from cervical disc herniation with less complication. The manipulation of PLDD is easy, safe and mini-invasive.

  8. Rapid radiative clearing of protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Haworth, Thomas J.; Clarke, Cathie J.; Owen, James E.

    2016-04-01

    The lack of observed transition discs with inner gas holes of radii greater than ˜50 au implies that protoplanetary discs dispersed from the inside out must remove gas from the outer regions rapidly. We investigate the role of photoevaporation in the final clearing of gas from low mass discs with inner holes. In particular, we study the so-called `thermal sweeping' mechanism which results in rapid clearing of the disc. Thermal sweeping was originally thought to arise when the radial and vertical pressure scalelengths at the X-ray heated inner edge of the disc match. We demonstrate that this criterion is not fundamental. Rather, thermal sweeping occurs when the pressure maximum at the inner edge of the dust heated disc falls below the maximum possible pressure of X-ray heated gas (which depends on the local X-ray flux). We derive new critical peak volume and surface density estimates for rapid radiative clearing which, in general, result in rapid dispersal happening less readily than in previous estimates. This less efficient clearing of discs by X-ray driven thermal sweeping leaves open the issue of what mechanism (e.g. far-ultraviolet heating) can clear gas from the outer disc sufficiently quickly to explain the non-detection of cold gas around weak line T Tauri stars.

  9. Colours of bulges and discs within galaxy clusters and the signature of disc fading on infall

    NASA Astrophysics Data System (ADS)

    Hudson, Michael J.; Stevenson, Jeffrey B.; Smith, Russell J.; Wegner, Gary A.; Lucey, John R.; Simard, Luc

    2010-11-01

    The origins of the bulge and disc components of galaxies are of primary importance to understanding galaxy formation. Here bulge-disc decomposition is performed simultaneously in B and R bands for 922 bright galaxies in eight nearby (z < 0.06) clusters with deep redshift coverage using photometry from the National Optical Astronomy Observatory (NOAO) Fundamental Plane Survey. The total galaxy colours follow a universal colour-magnitude relation (CMR). The discs of L* galaxies are 0.24 mag bluer in B - R than bulges. Bulges have a significant CMR slope while the CMR slope of discs is flat. Thus the slope of the CMR of the total light is driven primarily (60 per cent) by the bulge CMR, and to a lesser extent (40 per cent) by the change in the bulge-to-total ratio as a function of magnitude. The colours of the bulge and disc components do not depend on the bulge-to-total ratio, for galaxies with bulge-to-total ratios greater than 0.2. While the colours of the bulge components do not depend significantly on environment, the median colours of discs vary significantly, with discs in the cluster centre redder by 0.10 mag than those at the virial radius. Thus while star formation in bulges appears to be regulated primarily by mass-dependent, and hence presumably internal, processes, that of discs is affected by the cluster environment.

  10. Fragmentation of protoplanetary discs around M-dwarfs

    NASA Astrophysics Data System (ADS)

    Backus, Isaac; Quinn, Thomas

    2016-12-01

    We investigate the conditions required for planet formation via gravitational instability (GI) and protoplanetary disc (PPD) fragmentation around M-dwarfs. Using a suite of 64 SPH simulations with 106 particles, the parameter space of disc mass, temperature, and radius is explored, bracketing reasonable values based on theory and observation. Our model consists of an equilibrium, gaseous, and locally isothermal disc orbiting a central star of mass M* = M⊙/3. Discs with a minimum Toomre Q of Qmin ≲ 0.9 will fragment and form gravitationally bound clumps. Some previous literature has found Qmin < 1.3-1.5 to be sufficient for fragmentation. Increasing disc height tends to stabilize discs, and when incorporated into Q as Qeff ∝ Q(H/R)α for α = 0.18 is sufficient to predict fragmentation. Some discrepancies in the literature regarding Qcrit may be due to different methods of generating initial conditions (ICs). A series of 15 simulations demonstrates that perturbing ICs slightly out of equilibrium can cause discs to fragment for higher Q. Our method for generating ICs is presented in detail. We argue that GI likely plays a role in PPDs around M-dwarfs and that disc fragmentation at large radii is a plausible outcome for these discs.

  11. Time-dependent models of radiatively driven stellar winds. I - Nonlinear evolution of instabilities for a pure absorption model

    NASA Astrophysics Data System (ADS)

    Owocki, Stanley P.; Castor, John I.; Rybicki, George B.

    1988-12-01

    The authors describe results of numerical radiation-hydrodynamics simulations of the nonlinear evolution of instabilities in radiatively driven stellar winds. The wind is idealized as a spherically symmetric, isothermal flow driven by pure absorption of stellar radiation in a fixed ensemble of spectral lines. The simulations indicate that there is a strong tendency for the unstable flow to form rather sharp rarefactions in which the highest speed material has very low density. The growth of wave perturbations thus remains nearly exponential well beyond the linear regime, until the waves are kinematically steepened into strong shocks. The strongest shocks here are reverse shocks that arise to decelerate high-speed, rarefied flow as it impacts slower material that has been compressed into dense shells. The subsequent wind evolution shows a slow decay of the shocks and the gradual thermal decompression and interaction of the dense shells.

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

    NASA Astrophysics Data System (ADS)

    Joos, M.; Fromang, S.; Méheut, H.

    2015-10-01

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

  13. Cervical disc hernia operations through posterior laminoforaminotomy

    PubMed Central

    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 diagnosed with posterolateral cervical disc herniation and cervical spondylosis with foraminal stenosis causing radiculopathy operated by the posterior cervical keyhole laminoforaminotomy between the years 2010 and 2015. Results: The file records and the radiographic images of the 35 patients were assessed retrospectively. The mean age was 46.4 years (range: 34-66 years). Of the patients, 19 were males and 16 were females. In all of the patients, the neurologic deficit observed was radiculopathy. The posterolaterally localized disc herniations and the osteophytic structures were on the left side in 18 cases and on the right in 17 cases. In 10 of the patients, the disc level was at C5-6, in 18 at C6-7, in 2 at C3-4, in 2 at C4-5, in 1 at C7-T1, in 1 patient at both C5-6 and C6-7, and in 1 at both C4-5 and C5-6. In 14 of these 35 patients, both osteophytic structures and protruded disc herniation were present. Intervertebral foramen stenosis was present in all of the patients with osteophytes. Postoperatively, in 31 patients the complaints were relieved completely and four patients had complaints of neck pain and paresthesia radiating to the arm (the success of operation was 88.5%). On control examinations, there was no finding of instability or cervical kyphosis. Conclusion: Posterior cervical laminoforaminotomy is an alternative appropriate choice in both cervical soft disc herniations and cervical stenosis. PMID:27217655

  14. Collective instabilities

    SciTech Connect

    K.Y. Ng

    2003-08-25

    The lecture covers mainly Sections 2.VIII and 3.VII of the book ''Accelerator Physics'' by S.Y. Lee, plus mode-coupling instabilities and chromaticity-driven head-tail instability. Besides giving more detailed derivation of many equations, simple interpretations of many collective instabilities are included with the intention that the phenomena can be understood more easily without going into too much mathematics. The notations of Lee's book as well as the e{sup jwt} convention are followed.

  15. Distal Radioulnar Joint Instability

    PubMed Central

    Mirghasemi, Ali R.; Lee, Daniel J.; Rahimi, Narges; Rashidinia, Shervin

    2015-01-01

    Distal radioulnar joint (DRUJ) instability is a common clinical condition but a frequently missed diagnosis. Both surgical and nonsurgical treatments are possible for chronic cases of DRUJ instability. Nonsurgical treatment can be considered as the primary therapy in less active patients, while surgery should be considered to recover bone and ligament injuries if nonsurgical treatment fails to restore forearm stability and function. The appropriate choice of treatment depends on the individual patient and specific derangement of the DRUJ PMID:26328241

  16. Influence of electrical double-layer dispersion forces and size dependency on pull-in instability of clamped microplate immersed in ionic liquid electrolytes

    NASA Astrophysics Data System (ADS)

    Karimipour, I.; Beni, Yaghoub Tadi; Taheri, N.

    2017-10-01

    Plate-type clamped microplate is of the most common constructive elements for developing in-liquid-operating devices. While the electromechanical behavior of clamped microplate in non-liquid environments has exclusively been addressed in the literature, no theoretical studies have yet been conducted on precise modeling of the clamped microplate in electrolyte liquid. Herein, the electromechanical response and instability of the clamped microplate immersed in ionic electrolyte media are investigated. The electrochemical force field is determined using double layer theory and linearized Poisson-Boltzmann equation. The presence of dispersion forces, i.e., Casimir and van der Waals attractions, are included in the theoretical model considering the correction due to the presence of liquid media between the interacting surfaces (three-layer model). To this end, a kind of microplate has been designed, i.e., a square microplate with all edges clamped supported. The strain gradient elasticity is employed to model the size-dependent structural behavior of the clamped microplate. To solve the nonlinear constitutive equation of the system, Extended Kantorovich Method, is employed and the pull-in parameter of the microplate are extracted. Impacts of the dispersion forces and size effect on the instability characteristics are discussed as well as the effect of ion concentration and potential ratio. It is found that the significant difference between the pull-in instability parameters in the modified strain gradient theory and the classical theory for thin microplates is merely due to the consideration of size effect parameter in the modified strain gradient theory. To confirm the validity of formulations, the numerical values of the results are compared. The results predicted via the aforementioned approach are in excellent agreement with those in the literature. Some new examples are solved to demonstrate the applicability of the procedure.

  17. [Intervertebral instability].

    PubMed

    Colaiacomo, M C; Tortora, A; Di Biasi, C; Polettini, E; Casciani, E; Gualdi, G F

    2009-01-01

    The clinic diagnosis of degenerative lumbar intervertebral instability is a controversial topic and have not yet been clarified clinical criteria for to define this condition with accuracy. Although the lumbar pain is the most common symptom in patients who have lumbar intervertebral instability its clinical presentation is not specific; moreover in patients with lumbar pain there are no agreed signs and symptoms that can be truly attributable to instability. Despite better imaging techniques of testing spinal instability there is not a clear relations between radiologic signs of instability and clinical symptoms. It is, however, still far from unanimous definition of degenerative lumbar intervertebral instability accepted from all specialists involved in diagnosis and treatment of this condition; however, seem there is most agree about suspected vertebral instability. Nevertheless this unresolved topic, it is possible to state that imaging play an increasing role in diagnosis and management of patients with suspected instability. The aim of this study is to investigate the different imaging modalities most indicated in diagnosis if vertebral instability and whether degenerative change can be associated with lower back pain.

  18. Stellar irradiated discs and implications on migration of embedded planets. I. Equilibrium discs

    NASA Astrophysics Data System (ADS)

    Bitsch, B.; Crida, A.; Morbidelli, A.; Kley, W.; Dobbs-Dixon, I.

    2013-01-01

    Context. The strength and direction of migration of embedded low mass planets depends on the disc's thermodynamic state. It has been shown that, in discs where the viscous heating is balanced by radiative transport, the migration can be directed outwards, a process which extends the lifetime of growing planetary embryos. Aims: We investigate the influence of opacity and stellar irradiation on the disc thermodynamics. We focus on equilibrium discs, which have no net mass flux. Utilizing the resulting disc structure, we determine the regions of outward migration in the disc. Methods: We performed two-dimensional numerical simulations of equilibrium discs with viscous heating, radiative cooling, and stellar irradiation. We used the explicit/implicit hydrodynamical code NIRVANA that includes a full tensor viscosity and stellar irradiation, as well as a two temperature solver that includes radiation transport in the flux-limited diffusion approximation. The migration of embedded planets was studied by using torque formulae. Results: In the constant opacity case, our code reproduces the analytical results corresponding to a black-body disc: the stellar irradiation dominates in the outer regions - leading to flaring (H/r ∝ r2/7) - while the viscous heating dominates close to the star. In particular, we find that the inner edge of the disc should not be significantly puffed-up by the stellar irradiation. If the opacity depends on the local density and temperature, the structure of the disc is different, and several bumps in the aspect ratio H/r appear, due to transitions between different opacity regimes. The bumps in the disc structure are very important, as they can shield the outer disc from stellar irradiation. Conclusions: Stellar irradiation is an important factor for determining the disc structure and has dramatic consequences for the migration of embedded planets. Compared to discs with only viscous heating and radiative cooling, a stellar irradiated disc

  19. Importance of wave-number dependence of Biot numbers in one-sided models of evaporative Marangoni instability: Horizontal layer and spherical droplet

    NASA Astrophysics Data System (ADS)

    Machrafi, H.; Rednikov, A.; Colinet, P.; Dauby, P. C.

    2015-05-01

    A one-sided model of the thermal Marangoni instability owing to evaporation into an inert gas is developed. Two configurations are studied in parallel: a horizontal liquid layer and a spherical droplet. With the dynamic gas properties being admittedly negligible, one-sided approaches typically hinge upon quantifying heat and mass transfer through the gas phase by means of transfer coefficients (like in the Newton's cooling law), which in dimensionless terms eventually corresponds to using Biot numbers. Quite a typical arrangement encountered in the literature is a constant Biot number, the same for perturbations of different wavelengths and maybe even the same as for the reference state. In the present work, we underscore the relevance of accounting for its wave-number dependence, which is especially the case in the evaporative context with relatively large values of the resulting effective Biot number. We illustrate the effect in the framework of the Marangoni instability thresholds. As a concrete example, we consider HFE-7100 (a standard refrigerant) for the liquid and air for the inert gas.

  20. Effect of Size-Dependent Thermal Instability on Synthesis of Zn2 SiO4-SiOx Core–Shell Nanotube Arrays and Their Cathodoluminescence Properties

    PubMed Central

    2010-01-01

    Vertically aligned Zn2SiO4-SiOx(x < 2) core–shell nanotube arrays consisting of Zn2SiO4-nanoparticle chains encapsulated into SiOx nanotubes and SiOx-coated Zn2SiO4 coaxial nanotubes were synthesized via one-step thermal annealing process using ZnO nanowire (ZNW) arrays as templates. The appearance of different nanotube morphologies was due to size-dependent thermal instability and specific melting of ZNWs. With an increase in ZNW diameter, the formation mechanism changed from decomposition of “etching” to Rayleigh instability and then to Kirkendall effect, consequently resulting in polycrystalline Zn2SiO4-SiOx coaxial nanotubes, single-crystalline Zn2SiO4-nanoparticle-chain-embedded SiOx nanotubes, and single-crystalline Zn2SiO4-SiOx coaxial nanotubes. The difference in spatially resolved optical properties related to a particular morphology was efficiently documented by means of cathodoluminescence (CL) spectroscopy using a middle-ultraviolet emission at 310 nm from the Zn2SiO4 phase. PMID:20672064

  1. Importance of wave-number dependence of Biot numbers in one-sided models of evaporative Marangoni instability: Horizontal layer and spherical droplet.

    PubMed

    Machrafi, H; Rednikov, A; Colinet, P; Dauby, P C

    2015-05-01

    A one-sided model of the thermal Marangoni instability owing to evaporation into an inert gas is developed. Two configurations are studied in parallel: a horizontal liquid layer and a spherical droplet. With the dynamic gas properties being admittedly negligible, one-sided approaches typically hinge upon quantifying heat and mass transfer through the gas phase by means of transfer coefficients (like in the Newton's cooling law), which in dimensionless terms eventually corresponds to using Biot numbers. Quite a typical arrangement encountered in the literature is a constant Biot number, the same for perturbations of different wavelengths and maybe even the same as for the reference state. In the present work, we underscore the relevance of accounting for its wave-number dependence, which is especially the case in the evaporative context with relatively large values of the resulting effective Biot number. We illustrate the effect in the framework of the Marangoni instability thresholds. As a concrete example, we consider HFE-7100 (a standard refrigerant) for the liquid and air for the inert gas.

  2. State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling

    PubMed Central

    Kawamura, Kenji; Abe-Ouchi, Ayako; Motoyama, Hideaki; Ageta, Yutaka; Aoki, Shuji; Azuma, Nobuhiko; Fujii, Yoshiyuki; Fujita, Koji; Fujita, Shuji; Fukui, Kotaro; Furukawa, Teruo; Furusaki, Atsushi; Goto-Azuma, Kumiko; Greve, Ralf; Hirabayashi, Motohiro; Hondoh, Takeo; Hori, Akira; Horikawa, Shinichiro; Horiuchi, Kazuho; Igarashi, Makoto; Iizuka, Yoshinori; Kameda, Takao; Kanda, Hiroshi; Kohno, Mika; Kuramoto, Takayuki; Matsushi, Yuki; Miyahara, Morihiro; Miyake, Takayuki; Miyamoto, Atsushi; Nagashima, Yasuo; Nakayama, Yoshiki; Nakazawa, Takakiyo; Nakazawa, Fumio; Nishio, Fumihiko; Obinata, Ichio; Ohgaito, Rumi; Oka, Akira; Okuno, Jun’ichi; Okuyama, Junichi; Oyabu, Ikumi; Parrenin, Frédéric; Pattyn, Frank; Saito, Fuyuki; Saito, Takashi; Saito, Takeshi; Sakurai, Toshimitsu; Sasa, Kimikazu; Seddik, Hakime; Shibata, Yasuyuki; Shinbori, Kunio; Suzuki, Keisuke; Suzuki, Toshitaka; Takahashi, Akiyoshi; Takahashi, Kunio; Takahashi, Shuhei; Takata, Morimasa; Tanaka, Yoichi; Uemura, Ryu; Watanabe, Genta; Watanabe, Okitsugu; Yamasaki, Tetsuhide; Yokoyama, Kotaro; Yoshimori, Masakazu; Yoshimoto, Takayasu

    2017-01-01

    Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets. PMID:28246631

  3. Excess of Yra1 RNA-Binding Factor Causes Transcription-Dependent Genome Instability, Replication Impairment and Telomere Shortening.

    PubMed

    Gavaldá, Sandra; Santos-Pereira, José M; García-Rubio, María L; Luna, Rosa; Aguilera, Andrés

    2016-04-01

    Yra1 is an essential nuclear factor of the evolutionarily conserved family of hnRNP-like export factors that when overexpressed impairs mRNA export and cell growth. To investigate further the relevance of proper Yra1 stoichiometry in the cell, we overexpressed Yra1 by transforming yeast cells with YRA1 intron-less constructs and analyzed its effect on gene expression and genome integrity. We found that YRA1 overexpression induces DNA damage and leads to a transcription-associated hyperrecombination phenotype that is mediated by RNA:DNA hybrids. In addition, it confers a genome-wide replication retardation as seen by reduced BrdU incorporation and accumulation of the Rrm3 helicase. In addition, YRA1 overexpression causes a cell senescence-like phenotype and telomere shortening. ChIP-chip analysis shows that overexpressed Yra1 is loaded to transcribed chromatin along the genome and to Y' telomeric regions, where Rrm3 is also accumulated, suggesting an impairment of telomere replication. Our work not only demonstrates that a proper stoichiometry of the Yra1 mRNA binding and export factor is required to maintain genome integrity and telomere homeostasis, but suggests that the cellular imbalance between transcribed RNA and specific RNA-binding factors may become a major cause of genome instability mediated by co-transcriptional replication impairment.

  4. State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling.

    PubMed

    Kawamura, Kenji; Abe-Ouchi, Ayako; Motoyama, Hideaki; Ageta, Yutaka; Aoki, Shuji; Azuma, Nobuhiko; Fujii, Yoshiyuki; Fujita, Koji; Fujita, Shuji; Fukui, Kotaro; Furukawa, Teruo; Furusaki, Atsushi; Goto-Azuma, Kumiko; Greve, Ralf; Hirabayashi, Motohiro; Hondoh, Takeo; Hori, Akira; Horikawa, Shinichiro; Horiuchi, Kazuho; Igarashi, Makoto; Iizuka, Yoshinori; Kameda, Takao; Kanda, Hiroshi; Kohno, Mika; Kuramoto, Takayuki; Matsushi, Yuki; Miyahara, Morihiro; Miyake, Takayuki; Miyamoto, Atsushi; Nagashima, Yasuo; Nakayama, Yoshiki; Nakazawa, Takakiyo; Nakazawa, Fumio; Nishio, Fumihiko; Obinata, Ichio; Ohgaito, Rumi; Oka, Akira; Okuno, Jun'ichi; Okuyama, Junichi; Oyabu, Ikumi; Parrenin, Frédéric; Pattyn, Frank; Saito, Fuyuki; Saito, Takashi; Saito, Takeshi; Sakurai, Toshimitsu; Sasa, Kimikazu; Seddik, Hakime; Shibata, Yasuyuki; Shinbori, Kunio; Suzuki, Keisuke; Suzuki, Toshitaka; Takahashi, Akiyoshi; Takahashi, Kunio; Takahashi, Shuhei; Takata, Morimasa; Tanaka, Yoichi; Uemura, Ryu; Watanabe, Genta; Watanabe, Okitsugu; Yamasaki, Tetsuhide; Yokoyama, Kotaro; Yoshimori, Masakazu; Yoshimoto, Takayasu

    2017-02-01

    Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.

  5. Excess of Yra1 RNA-Binding Factor Causes Transcription-Dependent Genome Instability, Replication Impairment and Telomere Shortening

    PubMed Central

    Gavaldá, Sandra; Santos-Pereira, José M.; García-Rubio, María L.; Luna, Rosa; Aguilera, Andrés

    2016-01-01

    Yra1 is an essential nuclear factor of the evolutionarily conserved family of hnRNP-like export factors that when overexpressed impairs mRNA export and cell growth. To investigate further the relevance of proper Yra1 stoichiometry in the cell, we overexpressed Yra1 by transforming yeast cells with YRA1 intron-less constructs and analyzed its effect on gene expression and genome integrity. We found that YRA1 overexpression induces DNA damage and leads to a transcription-associated hyperrecombination phenotype that is mediated by RNA:DNA hybrids. In addition, it confers a genome-wide replication retardation as seen by reduced BrdU incorporation and accumulation of the Rrm3 helicase. In addition, YRA1 overexpression causes a cell senescence-like phenotype and telomere shortening. ChIP-chip analysis shows that overexpressed Yra1 is loaded to transcribed chromatin along the genome and to Y’ telomeric regions, where Rrm3 is also accumulated, suggesting an impairment of telomere replication. Our work not only demonstrates that a proper stoichiometry of the Yra1 mRNA binding and export factor is required to maintain genome integrity and telomere homeostasis, but suggests that the cellular imbalance between transcribed RNA and specific RNA-binding factors may become a major cause of genome instability mediated by co-transcriptional replication impairment. PMID:27035147

  6. Genomic Instability in Cancer

    PubMed Central

    Abbas, Tarek; Keaton, Mignon A.; Dutta, Anindya

    2013-01-01

    One of the fundamental challenges facing the cell is to accurately copy its genetic material to daughter cells. When this process goes awry, genomic instability ensues in which genetic alterations ranging from nucleotide changes to chromosomal translocations and aneuploidy occur. Organisms have developed multiple mechanisms that can be classified into two major classes to ensure the fidelity of DNA replication. The first class includes mechanisms that prevent premature initiation of DNA replication and ensure that the genome is fully replicated once and only once during each division cycle. These include cyclin-dependent kinase (CDK)-dependent mechanisms and CDK-independent mechanisms. Although CDK-dependent mechanisms are largely conserved in eukaryotes, higher eukaryotes have evolved additional mechanisms that seem to play a larger role in preventing aberrant DNA replication and genome instability. The second class ensures that cells are able to respond to various cues that continuously threaten the integrity of the genome by initiating DNA-damage-dependent “checkpoints” and coordinating DNA damage repair mechanisms. Defects in the ability to safeguard against aberrant DNA replication and to respond to DNA damage contribute to genomic instability and the development of human malignancy. In this article, we summarize our current knowledge of how genomic instability arises, with a particular emphasis on how the DNA replication process can give rise to such instability. PMID:23335075

  7. Anatomy of a population cycle: the role of density dependence and demographic variability on numerical instability and periodicity.

    PubMed

    Row, Jeffrey R; Wilson, Paul J; Murray, Dennis L

    2014-07-01

    Determining the causes of cyclic fluctuations in population size is a central tenet in population ecology and provides insights into population regulatory mechanisms. We have a firm understanding of how direct and delayed density dependence affects population stability and cyclic dynamics, but there remains considerable uncertainty in the specific processes contributing to demographic variability and consequent change in cyclic propensity. Spatiotemporal variability in cyclic propensity, including recent attenuation or loss of cyclicity among several temperate populations and the implications of habitat fragmentation and climate change on this pattern, highlights the heightened need to understand processes underlying cyclic variation. Because these stressors can differentially impact survival and productivity and thereby impose variable time delays in density dependence, there is a specific need to elucidate how demographic vital rates interact with the type and action of density dependence to contribute to population stability and cyclic variation. Here, we address this knowledge gap by comparing the stability of time series derived from general and species-specific (Canada lynx: Lynx canadensis; small rodents: Microtus, Lemmus and Clethrionomys spp.) matrix population models, which vary in their demographic rates and the direct action of density dependence. Our results reveal that density dependence acting exclusively on survival as opposed to productivity is destabilizing, suggesting that a shift in the action of population regulation toward reproductive output may decrease cyclic propensity and cycle amplitude. This result was the same whether delayed density dependence was pulsatile and acted on a single time period (e.g. t-1, t-2 or t-3) vs. more constant by affecting a successive range of years (e.g. t-1,…, t-3). Consistent with our general models, reductions in reproductive potential in both the lynx and small rodent systems led to notably large drops in

  8. Finite element parametric study of the influence of friction pad material and morphological characteristics on disc brake vibration phenomena

    NASA Astrophysics Data System (ADS)

    Forte, P.; Frendo, F.; Rodrigues, R. N.

    2016-09-01

    Since nowadays the NVH performance of vehicles has become an important priority, the noise radiating from brakes is considered a source of considerable passenger discomfort and dissatisfaction. Creep groan and squeal that show up with annoying vibrations and noise in specific frequency ranges are typical examples of self-excited brake vibrations caused by the stick-slip effect, the former, by the mode coupling of brake disc and friction pads or calliper, the latter. In both cases, the friction coefficient, which depends, among other factors, on the morphology of the mating surfaces and on the operating conditions, is a fundamental parameter but not the only one for the occurrence of the vibratory phenomena. Finite element complex eigenvalue parametric analyses were performed on a disc brake assembly to evaluate propensity to dynamic instability of brakes with multiple pads, as in railway brakes, as a function of the number of pads, pad shape and size, and material parameters.

  9. Weibel instability with nonextensive distribution

    SciTech Connect

    Qiu, Hui-Bin; Liu, Shi-Bing

    2013-10-15

    Weibel instability in plasma, where the ion distribution is isotropic and the electron component of the plasma possesses the anisotropic temperature distribution, is investigated based on the kinetic theory in context of nonextensive statistics mechanics. The instability growth rate is shown to be dependent on the nonextensive parameters of both electron and ion, and in the extensive limit, the result in Maxwellian distribution plasma is recovered. The instability growth rate is found to be enhanced as the nonextensive parameter of electron increases.

  10. Tuning directional dependent metal-insulator transitions in quasi-1D quantum wires with spin-orbit density wave instability

    NASA Astrophysics Data System (ADS)

    Das, Tanmoy

    2016-07-01

    We study directional dependent band gap evolutions and metal-insulator transitions (MITs) in model quantum wire systems within the spin-orbit density wave (SODW) model. The evolution of MIT is studied as a function of varying anisotropy between the intra-wire hopping ({{t}\\parallel} ) and inter-wire hopping ({{t}\\bot} ) with Rashba spin-orbit coupling. We find that as long as the anisotropy ratio (β ={{t}\\bot}/{{t}\\parallel} ) remains below 0.5, and the Fermi surface nesting is tuned to {{\\mathbf{Q}}1}=≤ft(π,0\\right) , an exotic SODW induced MIT easily develops, with its critical interaction strength increasing with increasing anisotropy. As β \\to 1 (2D system), the nesting vector switches to {{\\mathbf{Q}}2}=≤ft(π,π \\right) , making this state again suitable for an isotropic MIT. Finally, we discuss various physical consequences and possible applications of the directional dependent MIT.

  11. Temperature-dependent bias-stress-induced electrical instability of amorphous indium-gallium-zinc-oxide thin-film transistors

    NASA Astrophysics Data System (ADS)

    Qian, Hui-Min; Yu, Guang; Lu, Hai; Wu, Chen-Fei; Tang, Lan-Feng; Zhou, Dong; Ren, Fang-Fang; Zhang, Rong; Zheng, You-Liao; Huang, Xiao-Ming

    2015-07-01

    The time and temperature dependence of threshold voltage shift under positive-bias stress (PBS) and the following recovery process are investigated in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors. It is found that the time dependence of threshold voltage shift can be well described by a stretched exponential equation in which the time constant τ is found to be temperature dependent. Based on Arrhenius plots, an average effective energy barrier Eτstress = 0.72 eV for the PBS process and an average effective energy barrier Eτrecovery = 0.58 eV for the recovery process are extracted respectively. A charge trapping/detrapping model is used to explain the threshold voltage shift in both the PBS and the recovery process. The influence of gate bias stress on transistor performance is one of the most critical issues for practical device development. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB301900 and 2011CB922100) and the Priority Academic Program Development of Jiangsu Higher Education Institutions, China

  12. Shift in apparent contrast of disc at Secchi disc depth in coastal sea areas.

    PubMed

    Arakawa, Hisayuki; Inada, Mari; Choi, Sokjin; Narita, Miho

    2013-03-01

    The relationship between Secchi disc depth and amount of suspended material in seawater varies depending on the particular marine area. To identify the cause of this dependence, we calculated the apparent contrast (C (SD)) at each Secchi disc depth in different coastal sea areas. When the turbidity from the surface to the Secchi disc depth was uniform, the C (SD) was distributed in the range of 1.3 to 0.001 for a Secchi disc depth (Z (SD)) of 2-18 m. Z (SD) tended to decrease as C (SD) became larger. The dominant wavelength for the sea color was 475-500 nm for a Secchi disc depth of 13-18 m, and 500-575 nm for a Z(SD) of 2-6 m, shifting to longer wavelengths as the Secchi disc depth increased. That is, when Z (SD) decreased, the dominant wavelength of the sea color, and the C (SD) increased simultaneously. This phenomenon seems to occur because the contrast threshold for the human eye is higher at longer wavelengths. In other words, the contrast threshold is visibly indistinguishable when the apparent contrast in ocean waters with low Secchi disc depths is high. This phenomenon occurs because the human eye is affected by the color of the sea.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  14. Equilibrium Electroconvective Instability

    NASA Astrophysics Data System (ADS)

    Rubinstein, I.; Zaltzman, B.

    2015-03-01

    Since its prediction 15 years ago, hydrodynamic instability in concentration polarization at a charge-selective interface has been attributed to nonequilibrium electro-osmosis related to the extended space charge which develops at the limiting current. This attribution had a double basis. On the one hand, it has been recognized that neither equilibrium electro-osmosis nor bulk electroconvection can yield instability for a perfectly charge-selective solid. On the other hand, it has been shown that nonequilibrium electro-osmosis can. The first theoretical studies in which electro-osmotic instability was predicted and analyzed employed the assumption of perfect charge selectivity for the sake of simplicity and so did the subsequent studies of various time-dependent and nonlinear features of electro-osmotic instability. In this Letter, we show that relaxing the assumption of perfect charge selectivity (tantamount to fixing the electrochemical potential of counterions in the solid) allows for the equilibrium electroconvective instability. In addition, we suggest a simple experimental test for determining the true, either equilibrium or nonequilibrium, origin of instability in concentration polarization.

  15. Holographic optical disc

    NASA Astrophysics Data System (ADS)

    Zhou, Gan; An, Xin; Pu, Allen; Psaltis, Demetri; Mok, Fai H.

    1999-11-01

    The holographic disc is a high capacity, disk-based data storage device that can provide the performance for next generation mass data storage needs. With a projected capacity approaching 1 terabit on a single 12 cm platter, the holographic disc has the potential to become a highly efficient storage hardware for data warehousing applications. The high readout rate of holographic disc makes it especially suitable for generating multiple, high bandwidth data streams such as required for network server computers. Multimedia applications such as interactive video and HDTV can also potentially benefit from the high capacity and fast data access of holographic memory.

  16. Vertical cup/disc ratio in relation to optic disc size: its value in the assessment of the glaucoma suspect

    PubMed Central

    Garway-Heath, D.; Ruben, S.; Viswanathan, A.; Hitchings, R.

    1998-01-01

    AIMS—The vertical cup/disc ratio (CDR) has long been used in the assessment of the glaucoma suspect, though the wide range of CDR values in the normal population limits its use. Cup size is related physiologically to disc size and pathologically to glaucomatous damage. Disc size can be measured at the slit lamp as the vertical disc diameter (DD). The ability of the CDR, in relation to DD, to identify glaucomatous optic discs was investigated.
METHODS—88 normal, 53 early glaucoma, and 59 ocular hypertensive subjects underwent stereoscopic optic disc photography and clinical biometry. Photographs were analysed in a masked fashion by computer assisted planimetry. The relation between vertical cup diameter and DD was explored by linear regression, and expressed in terms of CDR. The upper limit of normal was defined by the 95% prediction intervals of this regression (method 1) and by the upper 97.5 percentile for CDR (method 2). The sensitivity and specificity of CDR to identify an optic disc as glaucomatous was tested with these disc size dependent and disc size independent cut offs in small, medium, and large discs.
RESULTS—The CDR was related to DD by the equation CDR = (−1.31 + (1.194 × DD))/DD. The sensitivity in small, medium, and large discs was 80%, 60%, and 38% respectively for method 1 and 33%, 67%, and 63% respectively for method 2. Specificity was 98.9% (method 1) and 97.7% (method 2).
CONCLUSIONS—The CDR, relative to disc size, is useful clinically, especially to assist in identifying small glaucomatous discs.

 Keywords: cup/disc ratio; glaucoma; imaging PMID:9924296

  17. Building disc structure and galaxy properties through angular momentum: the DARK SAGE semi-analytic model

    NASA Astrophysics Data System (ADS)

    Stevens, Adam R. H.; Croton, Darren J.; Mutch, Simon J.

    2016-09-01

    We present the new semi-analytic model of galaxy evolution, DARK SAGE, a heavily modified version of the publicly available SAGE code. The model is designed for detailed evolution of galactic discs. We evolve discs in a series of annuli with fixed specific angular momentum, which allows us to make predictions for the radial and angular-momentum structure of galaxies. Most physical processes, including all channels of star formation and associated feedback, are performed in these annuli. We present the surface density profiles of our model spiral galaxies, both as a function of radius and specific angular momentum, and find that the discs naturally build a pseudo-bulge-like component. Our main results are focused on predictions relating to the integrated mass-specific angular momentum relation of stellar discs. The model produces a distinct sequence between these properties in remarkable agreement with recent observational literature. We investigate the impact Toomre disc instabilities have on shaping this sequence and find they are crucial for regulating both the mass and spin of discs. Without instabilities, high-mass discs would be systematically deficient in specific angular momentum by a factor of ˜2.5, with increased scatter. Instabilities also appear to drive the direction in which the mass-spin sequence of spiral galaxy discs evolves. With them, we find galaxies of fixed mass have higher specific angular momentum at later epochs.

  18. Research on aviation fuel instability

    NASA Technical Reports Server (NTRS)

    Baker, C. E.; Bittker, D. A.; Cohen, S. M.; Seng, G. T.

    1983-01-01

    The underlying causes of fuel thermal degradation are discussed. Topics covered include: nature of fuel instability and its temperature dependence, methods of measuring the instability, chemical mechanisms involved in deposit formation, and instrumental methods for characterizing fuel deposits. Finally, some preliminary thoughts on design approaches for minimizing the effects of lowered thermal stability are briefly discussed.

  19. The structure of protoplanetary discs around evolving young stars

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  20. Molecular Mechanisms of Biological Aging in Intervertebral Discs

    PubMed Central

    Vo, Nam V.; Hartman, Robert A.; Patil, Prashanti R.; Risbud, Makarand V.; Kletsas, Dimitris; Iatridis, James C.; Hoyland, Judith A.; Le Maitre, Christine L.; Sowa, Gwendolyn A.; Kang, James D.

    2016-01-01

    Advanced age is the greatest risk factor for the majority of human ailments, including spine-related chronic disability and back pain, which stem from age-associated intervertebral disc degeneration (IDD). Given the rapid global rise in the aging population, understanding the biology of intervertebral disc aging in order to develop effective therapeutic interventions to combat the adverse effects of aging on disc health is now imperative. Fortunately, recent advances in aging research have begun to shed light on the basic biological process of aging. Here we review some of these insights and organize the complex process of disc aging into three different phases to guide research efforts to understand the biology of disc aging. The objective of this review is to provide an overview of the current knowledge and the recent progress made to elucidate specific molecular mechanisms underlying disc aging. In particular, studies over the last few years have uncovered cellular senescence and genomic instability as important drivers of disc aging. Supporting evidence comes from DNA repair-deficient animal models that show increased disc cellular senescence and accelerated disc aging. Additionally, stress-induced senescent cells have now been well documented to secrete catabolic factors, which can negatively impact the physiology of neighboring cells and ECM. These along with other molecular drivers of aging are reviewed in depth to shed crucial insights into the underlying mechanisms of age-related disc degeneration. We also highlight molecular targets for novel therapies and emerging candidate therapeutics that may mitigate age-associated IDD. PMID:26890203

  1. Inhibition of methionine adenosyltransferase II induces FasL expression, Fas-DISC formation and caspase-8-dependent apoptotic death in T leukemic cells.

    PubMed

    Jani, Tanvi S; Gobejishvili, Leila; Hote, Prachi T; Barve, Aditya S; Joshi-Barve, Swati; Kharebava, Giorgi; Suttles, Jill; Chen, Theresa; McClain, Craig J; Barve, Shirish

    2009-03-01

    Methionine adenosyltransferase II (MAT II) is a key enzyme in cellular metabolism and catalyzes the formation of S-adenosylmethionine (SAMe) from L-methionine and ATP. Normal resting T lymphocytes have minimal MAT II activity, whereas activated proliferating T lymphocytes and transformed T leukemic cells show significantly enhanced MAT II activity. This work was carried out to examine the role of MAT II activity and SAMe biosynthesis in the survival of leukemic T cells. Inhibition of MAT II and the resultant decrease in SAMe levels enhanced expression of FasL mRNA and protein, and induced DISC (Death Inducing Signaling Complex) formation with FADD (Fas-associated Death Domain) and procaspase-8 recruitment, as well as concomitant increase in caspase-8 activation and decrease in c-FLIP(s) levels. Fas-initiated signaling induced by MAT II inhibition was observed to link to the mitochondrial pathway via Bid cleavage and to ultimately lead to increased caspase-3 activation and DNA fragmentation in these cells. Furthermore, blocking MAT 2A mRNA expression, which encodes the catalytic subunits of MAT II, using a small-interfering RNA approach enhanced FasL expression and cell death, validating the essential nature of MAT II activity in the survival of T leukemic cells.

  2. Be discs in binary systems - I. Coplanar orbits

    NASA Astrophysics Data System (ADS)

    Panoglou, Despina; Carciofi, Alex C.; Vieira, Rodrigo G.; Cyr, Isabelle H.; Jones, Carol E.; Okazaki, Atsuo T.; Rivinius, Thomas

    2016-09-01

    Be stars are surrounded by outflowing circumstellar matter structured in the form of decretion discs. They are often members of binary systems, where it is expected that the decretion disc interacts both radiatively and gravitationally with the companion. In this work we study how various orbital (period, mass ratio and eccentricity) and disc (viscosity) parameters affect the disc structure in coplanar binaries. The main effects of the secondary on the disc are its truncation and the accumulation of material inwards of truncation. We find two limiting cases with respect to the effects of eccentricity: in circular or nearly circular prograde orbits, the disc maintains a rotating, constant in shape, configuration, which is locked to the orbital phase. The disc structure appears smaller in size, more elongated and more massive for small viscosity parameter, small orbital separation and/or high mass ratio. In highly eccentric orbits, the effects are more complex, with the disc structure strongly dependent on the orbital phase. We also studied the effects of binarity in the disc continuum emission. Since the infrared and radio SED are sensitive to the disc size and density slope, the truncation and matter accumulation result in considerable modifications in the emergent spectrum. We conclude that binarity can serve as an explanation for the variability exhibited in observations of Be stars, and that our model can be used to detect invisible companions.

  3. DaDyn-RS: a tool for the time-dependent simulation of damage, fluid pressure and long-term instability in alpine rock slopes

    NASA Astrophysics Data System (ADS)

    Riva, Federico; Agliardi, Federico; Amitrano, David; Crosta, Giovanni B.

    2017-04-01

    Large mountain slopes in alpine environments undergo a complex long-term evolution from glacial to postglacial environments, through a transient period of paraglacial readjustment. During and after this transition, the interplay among rock strength, topographic relief, and morpho-climatic drivers varying in space and time can lead to the development of different types of slope instability, from sudden catastrophic failures to large, slow, long-lasting yet potentially catastrophic rockslides. Understanding the long-term evolution of large rock slopes requires accounting for the time-dependence of deglaciation unloading, permeability and fluid pressure distribution, displacements and failure mechanisms. In turn, this is related to a convincing description of rock mass damage processes and to their transition from a sub-critical (progressive failure) to a critical (catastrophic failure) character. Although mechanisms of damage occurrence in rocks have been extensively studied in the laboratory, the description of time-dependent damage under gravitational load and variable external actions remains difficult. In this perspective, starting from a time-dependent model conceived for laboratory rock deformation, we developed Dadyn-RS, a tool to simulate the long-term evolution of real, large rock slopes. Dadyn-RS is a 2D, FEM model programmed in Matlab, which combines damage and time-to-failure laws to reproduce both diffused damage and strain localization meanwhile tracking long-term slope displacements from primary to tertiary creep stages. We implemented in the model the ability to account for rock mass heterogeneity and property upscaling, time-dependent deglaciation, as well as damage-dependent fluid pressure occurrence and stress corrosion. We first tested DaDyn-RS performance on synthetic case studies, to investigate the effect of the different model parameters on the mechanisms and timing of long-term slope behavior. The model reproduces complex interactions between

  4. Artificial Disc Replacement

    MedlinePlus

    ... also disc replacements designed for use in the cervical spine (the neck). These devices have only been used ... of your spine increases the risk of significant injury during this type of spinal surgery. Back pain ...

  5. Evolution of an accretion disc in binary black hole systems

    NASA Astrophysics Data System (ADS)

    Kimura, Shigeo S.; Takahashi, Sanemichi Z.; Toma, Kenji

    2017-03-01

    We investigate evolution of an accretion disc in binary black hole (BBH) systems and possible electromagnetic counterparts of the gravitational waves from mergers of BBHs. Perna et al. proposed a novel evolutionary scenario of an accretion disc in BBHs in which a disc eventually becomes 'dead', i.e. the magnetorotational instability (MRI) becomes inactive. In their scenario, the dead disc survives until a few seconds before the merger event. We improve the dead disc model and propose another scenario, taking account of effects of the tidal torque from the companion and the critical ionization degree for MRI activation more carefully. We find that the mass of the dead disc is much lower than that in the Perna's scenario. When the binary separation sufficiently becomes small, the mass inflow induced by the tidal torque reactivates MRI, restarting mass accretion on to the black hole. We also find that this disc 'revival' happens more than thousands of years before the merger. The mass accretion induced by the tidal torque increases as the separation decreases, and a relativistic jet could be launched before the merger. The emissions from these jets are too faint compared to gamma-ray bursts, but detectable if the merger events happen within ≲10 Mpc or if the masses of the black holes are as massive as ∼105 M⊙.

  6. Quantitative determination of valproic acid in postmortem blood samples--evidence of strong matrix dependency and instability.

    PubMed

    Kiencke, Verena; Andresen-Streichert, Hilke; Müller, Alexander; Iwersen-Bergmann, Stefanie

    2013-11-01

    Most of the daily work of forensic toxicologists deals with fatal cases resulting from overdoses of licit and illicit drugs. However, another reason for fatalities in patients suffering from epilepsy can be undetectable or subtherapeutic levels of antiepileptic drugs. Some studies have shown a correlation between "sudden unexpected death in epilepsy" (SUDEP) and the ineffective treatment of epilepsy. Low levels of antiepileptic drugs may be a risk factor for SUDEP. The death of a psychiatric patient also suffering from epilepsy inspired the investigation. Subsequent to the death of the patient, the doctor was accused of providing inadequate therapy for epilepsy. The patient was to be treated with valproic acid. We developed and validated a simple method of determining valproic acid levels by gas chromatography-mass spectrometry for serum, but a transfer of the method from serum to postmortem whole blood failed. The method had to be modified and revalidated for postmortem whole blood specimens. A stability study of valproic acid in postmortem blood was conducted, showing a decline of valproic acid levels by 85 % after storage at room temperature for 28 days. During the storage time, the blood samples showed changes in consistency. Depending on the stage of decomposition, it is necessary to perform a determination by standard addition with an equilibration time of 4 h before extraction to achieve reliable results. For a proper interpretation of quantitative results, it is necessary to keep the postmortem decline of valproic acid concentrations in mind.

  7. Bryan total disc arthroplasty: a replacement disc for cervical disc disease

    PubMed Central

    Wenger, Markus; Markwalder, Thomas-Marc

    2010-01-01

    Total disc arthroplasty is a new option in the treatment of cervical degenerative disc disease. Several types of cervical disc prostheses currently challenge the gold-standard discectomy and fusion procedures. This review describes the Bryan Cervical Disc System and presents the Bryan prosthesis, its indications, surgical technique, complications, and outcomes, as given in the literature. PMID:22915917

  8. Fingering instability of a suspension film spreading on a spinning disk

    NASA Astrophysics Data System (ADS)

    Kulkarni, Mayuresh; Sahoo, Subhadarshinee; Doshi, Pankaj; Orpe, Ashish

    2016-11-01

    We have experimentally investigated the spreading of a suspension drop when rotated atop a spinning disk using flow visualization techniques. The suspension is made of 50 +/- 10 micron glass beads suspended in a low viscosity, partially wetting Newtonian liquid having same density as the glass beads. The suspension drop is placed centrally on a horizontal disc and the disc is then rotated at a desired speed. The spreading behavior is captured using a high speed camera and the acquired images are analysed to find the edges of the spreading film. For all the particle volume fractions (ϕp) studied, the suspension drops spread radially until they reach a critical radius, following which the contact line develops instabilities which further grow into fingers. The critical radius for the onset of instability shows an increase with increase in the particle fraction (ϕp) before decreasing slightly at the highest value of ϕp studied, while the instability wavelength (λ) exhibits a non-monotonic dependence. The value of λ is close to that for a partially wetting liquid at lower ϕp, it decreases with increasing ϕp to a minimum before increasing again at the largest ϕp.

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

    NASA Astrophysics Data System (ADS)

    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.

  10. Time-dependent release of cobalt and chromium ions into the serum following implantation of the metal-on-metal Maverick type artificial lumbar disc (Medtronic Sofamor Danek).

    PubMed

    Zeh, Alexander; Becker, Claudia; Planert, Michael; Lattke, Peter; Wohlrab, David

    2009-06-01

    In total hip endoprosthetics and consequently for TDA, metal-on-metal combinations are used with the aim of reducing wear debris. In metal-on-metal TDA the release of metal ions has until now been secondary to the main discussion. In order to investigate the ion release following the implantation of the metal-on-metal Maverick type artificial lumbar disc we measured the serum cobalt and chromium concentration following implantation of 15 Maverick TDAs (monosegmental L5/S1, n = 5; bisegmental L4/5 and L5/S1, n = 5; average age 36.5 years). Five healthy subjects (no metal implants) acted as a control group. The two measurements of the metals were carried out using the absorption spectrometry after an average of 14.8 and 36.7 months. In summary, the concentrations of cobalt and chromium ions in the serum at both follow-ups amounted on average to 3.3 microg/l (SD 2.6) for cobalt and 2.2 microg/l (SD 1.5) for chromium. These figures are similar to the figures shown in the literature following the implantation of metal-on-metal THA. After a comparison to the control group, both the chromium and cobalt levels in the serum showed visible increases regarding the first and the second follow-up. As there is still a significant release of cobalt and chromium into the serum after an average follow-up of 36.7 months a persistent release of these ions must be taken into consideration. Despite the evaluation of the systemic and local effects of the release of Cr/Co from orthopaedic implants has not yet been concluded, one should take into consideration an explanation given to patients scheduled for the implantation of a metal-on-metal TDA about these results and the benefits/risks of alternative combinations of gliding contact surfaces.

  11. The ability of a protostellar disc to fragment and the properties of molecular cloud cores

    NASA Astrophysics Data System (ADS)

    Liu, Chunjian; Li, Min; Yao, Zhen; Mao, Xiaodong

    2017-01-01

    We explore the ability of a protostellar disc to fragment using an evolutionary disc model. Our disc model includes the mass influx from a molecular cloud core, the irradiation from the central star, the magnetorotational instability (MRI), and the gravitational instability (Kratter et al. in Astrophys. J. 681:375, 2008). We use the fragmentation criterion of Gammie (Astrophys. J. 553:174, 2001) and Rafikov (Astrophys. J. 621:L69, 2005) to judge whether or not a protostellar disc can fragment. We find that there is a link between whether a protostellar disc can fragment and the properties of the molecular cloud cores (angular velocity ω, temperature T_{core}, and mass M_{core}). In the parameter space ω-M_{core}, there is a critical value ω_{crit}, which divides the parameter space into two regions: one is the fragmentation region, the other is the non-fragmentation region. The protostellar disc can only fragment when ω> ω_{crit}. The reason can be understood as follows. The protostellar disc is formed from the gravitational collapse of a molecular cloud core, the properties of the molecular cloud core determine the properties of the protostellar disc. Thus the two categories of protostellar discs correspond to two categories of molecular cloud cores. Moreover, we find that ω_{crit} is approximately a linear function of M_{core} in log-scale coordinates.

  12. Angular Momentum in the Formation of Disc Galaxies

    NASA Astrophysics Data System (ADS)

    Luo, Zhi-Jian; Shu, Cheng-Gang

    2004-03-01

    Within the current framework of disc galaxy formation, we discuss the resulted surface-density profiles according to the theoretical angular momentum distributions (AMDs) presented by Bullock et al. [Astrophys. J. 555 (2001) 240(B01)] for the LambdaCDM cosmology in both spherical and cylindrical coordinates. It is found that the derived surface density distribution of a disc in the outer region is in general similar to an exponential disc for both the theoretical AMDs. In the central region, the results from both the theoretical AMDs are inconsistent with observations whether the disc bar-instability is taken into account or not. The cylindrical form of the theoretical AMD leads to the bar-instability more easily for a galaxy than that for spherical AMD, which could result in a more massive bulge. After comparing the model predictions with our Milky Way Galaxy, we find that the theoretical AMDs predict larger mass fractions of baryons with low angular momentum than the observed ones, which would lead to the disc sizes being smaller. Two possible processes which could solve the angular momentum problem are discussed. EHPRG Award Lecture.

  13. Fu Ori outbursts and the planet-disc mass exchange

    NASA Astrophysics Data System (ADS)

    Nayakshin, Sergei; Lodato, Giuseppe

    2012-10-01

    It has been recently proposed that giant protoplanets migrating inwards through the disc more rapidly than they contract could be tidally disrupted when they fill their Roche lobes ˜0.1 au away from their parent protostars. Here we consider the process of mass and angular momentum exchange between the tidally disrupted planet and the surrounding disc in detail. We find that the planet's adiabatic mass-radius relation and its ability to open a deep gap in the disc determine whether the disruption proceeds as a sudden runaway or a balanced quasi-static process. In the latter case, the planet feeds the inner disc through its Lagrangian L1 point like a secondary star in a stellar binary system. As the planet loses mass, it gains specific angular momentum and normally migrates in the outward direction until the gap closes. Numerical experiments show that planet disruption outbursts are preceded by long 'quiescent' periods during which the disc inward of the planet is empty. The hole in the disc is created when the planet opens a deep gap, letting the inner disc to drain on to the star while keeping the outer one stalled behind the planet. We find that the mass-losing planet embedded in a realistic protoplanetary disc spawns an extremely rich set of variability patterns. In a subset of parameter space, there is a limit cycle behaviour caused by non-linear interaction between the planet mass-loss and the disc hydrogen ionization instability. We suggest that tidal disruptions of young massive planets near their stars may be responsible for the observed variability of young accreting protostars such as FU Ori, EXor and T Tauri stars in general.

  14. Evolution of gas in debris discs

    NASA Astrophysics Data System (ADS)

    Kral, Quentin; Wyatt, Mark; Pringle, Jim

    2015-12-01

    A non negligible quantity of gas has been discovered in an increasing number of debris disc systems. ALMA high sensitivity and high resolution is changing our perception of the gaseous component of debris discs as CO is discovered in systems where it should be rapidly photodissociated. It implies that there is a replenishment mechanism and that the observed gas is secondary. Past missions such as Herschel probed the atomic part of the gas through O I and C II emission lines. Gas science in debris discs is still in its infancy, and these new observations raise a handful of questions concerning the mechanisms to create the gas and about its evolution in the planetary system when it is released. The latter question will be addressed in this talk as a self-consistent gas evolution scenario is proposed and is compared to observations for the peculiar case of β Pictoris.Our model proposes that carbon and oxygen within debris discs are created due to photodissociation of CO which is itself created from the debris disc dust (due to grain-grain collisions or photodesorption). The evolution of the carbon atoms is modelled as viscous spreading, with viscosity parameterised using an α model. The temperature, ionisation fraction and population levels of carbon are followed with a PDR model called Cloudy, which is coupled to the dynamical viscous α model. Only carbon gets ionised due to its lower ionisation potential than oxygen. The carbon gas disc can end up with a high ionisation fraction due to strong FUV radiation field. A high ionisation fraction means that the magnetorotational instability (MRI) is very active, so that α is very high. Gas density profiles can be worked out for different input parameters such as the α value, the CO input rate, the location of the input and the incoming radiation field. Observability predictions can be made for future observations, and our model is tested on β Pictoris observations. This new gas evolution model fits the carbon and CO

  15. Nonlinear transient and chaotic interactions in disc brake squeal

    NASA Astrophysics Data System (ADS)

    Oberst, S.; Lai, J. C. S.

    2015-04-01

    In automotive disc-brake squeal, most numerical studies have been focussed on the prediction of unstable vibration modes in the frequency domain using the complex eigenvalue analysis. However, the magnitude of the positive real part of a complex eigenvalue is an unreliable indicator of squeal occurrence. Although nonlinearities have been shown to play a significant role in brake squeal, transient nonlinear time domain analyses have rarely been applied owing to high computational costs. Here the complex eigenvalue analysis, the direct steady-state analysis and the transient nonlinear time domain analysis are applied to an isotropic pad-on-disc finite element model representing a simple model of a brake system. While in this investigation, in-plane pad-mode instabilities are not detected by the complex eigenvalue analysis, the dissipated energy obtained by the direct steady-state analysis of the model subjected to harmonic contact pressure excitation is negative at frequencies of pad modes, indicating a potential for instabilities. Transient nonlinear time domain analysis of the pad and disc dynamics reveal that in-plane pad vibrations excite a dominant out-of-plane disc mode. For intermittently chaotic pad motion, the disc dynamics is quasi-periodic; and for chaotic motion of the pad, a toroidal attractor is found for the disc's out-of-plane motion. Nonlinear interactions between the pad and the disc highlight that different parts in a brake system display different dynamic behaviour and need to be analysed separately. The type II intermittency route to chaos could be the cause for the experimentally observed instantaneous mode squeal.

  16. The effect of radiative feedback on disc fragmentation

    NASA Astrophysics Data System (ADS)

    Mercer, Anthony; Stamatellos, Dimitris

    2017-02-01

    Protostellar discs may become massive enough to fragment producing secondary low-mass objects: planets, brown dwarfs and low-mass stars. We study the effect of radiative feedback from such newly formed secondary objects using radiative hydrodynamic simulations. We compare the results of simulations without any radiative feedback from secondary objects with those where two types of radiative feedback are considered: (i) continuous and (ii) episodic. We find that (i) continuous radiative feedback stabilizes the disc and suppresses further fragmentation, reducing the number of secondary objects formed; (ii) episodic feedback from secondary objects heats and stabilizes the disc when the outburst occurs, but shortly after the outburst stops, the disc becomes unstable and fragments again. However, fewer secondary objects are formed compared to the case without radiative feedback. We also find that the mass growth of secondary objects is mildly suppressed due to the effect of their radiative feedback. However, their mass growth also depends on where they form in the disc and on their subsequent interactions, such that their final masses are not drastically different from the case without radiative feedback. We find that the masses of secondary objects formed by disc fragmentation are from a few MJ to a few 0.1 M⊙. Planets formed by fragmentation tend to be ejected from the disc. We conclude that planetary-mass objects on wide orbits (wide-orbit planets) are unlikely to form by disc fragmentation. Nevertheless, disc fragmentation may be a significant source of free-floating planets and brown dwarfs.

  17. Effects of disc mid-plane evolution on CO snowline location

    NASA Astrophysics Data System (ADS)

    Panić, O.; Min, M.

    2017-05-01

    Temperature changes in the planet forming disc mid-planes carry important physico-chemical consequences, such as the effect on the locations of the condensation fronts of molecules - the snowlines. Snowlines impose major chemical gradients and possibly foster grain growth. The aim of this paper is to understand how disc mid-plane temperature changes with gas and dust evolution, and identify trends that may influence planet formation or allow to constrain disc evolution observationally. We calculate disc temperature, hydrostatic equilibrium and dust settling in a mutually consistent way from a grid of disc models at different stages of gas loss, grain growth and hole opening. We find that the CO snowline location depends very strongly on disc properties. The CO snowline location migrates closer to the star for increasing degrees of gas dispersal and dust growth. Around a typical A-type star, the snowline can be anywhere between several tens and a few hundred au, depending on the disc properties such as gas mass and grain size. In fact, gas loss is as efficient as dust evolution in settling discs, and flat discs may be gas-poor counterparts of flared discs. Our results, in the context of different pre-main-sequence evolution of the luminosity in low- and intermediate-mass stars suggest very different thermal (and hence chemical) histories in these two types of discs. Discs of T Tauri stars settle and cool down, while discs of Herbig Ae stars may remain rather warm throughout the pre-main sequence.

  18. The Galactic stellar disc

    NASA Astrophysics Data System (ADS)

    Feltzing, S.; Bensby, T.

    2008-12-01

    The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular, we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high-resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick discs have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reach high above the Galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well-mixed gas that had been homogenized over large volumes. We find some evidence that suggest that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H], we show that the solar neighbourhood contains metal-rich, high velocity stars that are very likely associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the groups and streams so far identified in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Also based on observations collected at the Nordic Optical Telescope on La Palma, Spain, and at the European Southern Observatories on La Silla and Paranal, Chile, Proposals no. 65.L-0019(B), 67.B-0108(B), 69.B-0277.

  19. Clumpy disc and bulge formation

    NASA Astrophysics Data System (ADS)

    Perez, Josefa; Valenzuela, Octavio; Tissera, Patricia B.; Michel-Dansac, Leo

    2013-11-01

    We present a set of hydrodynamical/N-body controlled simulations of isolated gas-rich galaxies that self-consistently include supernova (SN) feedback and a detailed chemical evolution model, both tested in cosmological simulations. The initial conditions are motivated by the observed star-forming galaxies at z ˜ 2-3. We find that the presence of a multiphase interstellar media in our models promotes the growth of disc instability favouring the formation of clumps which, in general, are not easily disrupted on time-scales compared to the migration time. We show that stellar clumps migrate towards the central region and contribute to form a classical-like bulge with a Sérsic index, n > 2. Our physically motivated SN feedback has a mild influence on clump survival and evolution, partially limiting the mass growth of clumps as the energy released per SN event is increased, with the consequent flattening of the bulge profile. This regulation does not prevent the building of a classical-like bulge even for the most energetic feedback tested. Our SN feedback model is able to establish self-regulated star formation, producing mass-loaded outflows and stellar age spreads comparable to observations. We find that the bulge formation by clumps may coexist with other channels of bulge assembly such as bars and mergers. Our results suggest that galactic bulges could be interpreted as composite systems with structural components and stellar populations storing archaeological information of the dynamical history of their galaxy.

  20. Self-organisation in protoplanetary discs. Global, non-stratified Hall-MHD simulations

    NASA Astrophysics Data System (ADS)

    Béthune, William; Lesur, Geoffroy; Ferreira, Jonathan

    2016-05-01

    Context. Recent observations have revealed organised structures in protoplanetary discs, such as axisymmetric rings or horseshoe concentrations, evocative of large-scale vortices. These structures are often interpreted as the result of planet-disc interactions. However, these discs are also known to be unstable to the magneto-rotational instability (MRI) which is believed to be one of the dominant angular momentum transport mechanism in these objects. It is therefore natural to ask whether the MRI itself could produce these structures without invoking planets. Aims: The nonlinear evolution of the MRI is strongly affected by the low ionisation fraction in protoplanetary discs. The Hall effect in particular, which is dominant in dense and weakly ionised parts of these objects, has been shown to spontaneously drive self-organising flows in local, shearing box simulations. Here, we investigate the behaviour of global MRI-unstable disc models dominated by the Hall effect and characterise their dynamics. Methods: We validated our implementation of the Hall effect into the PLUTO code with predictions from a spectral method in cylindrical geometry. We then performed 3D unstratified Hall-MHD simulations of Keplerian discs for a broad range of Hall, Ohmic, and ambipolar Elsasser numbers. Results: We confirm the transition from a turbulent to an organised state as the intensity of the Hall effect is increased. We observe the formation of zonal flows, their number depending on the available magnetic flux and on the intensity of the Hall effect. For intermediate Hall intensity, the flow self-organises into long-lived magnetised vortices. Neither the addition of a toroidal field nor Ohmic or ambipolar diffusion change this picture drastically in the range of parameters we have explored. Conclusions: Self-organisation by the Hall effect is a robust phenomenon in global non-stratified simulations. It is able to quench turbulent transport and spontaneously produce axisymmetric

  1. Grain charging in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Ilgner, M.

    2012-02-01

    Context. Recent work identified a growth barrier for dust coagulation that originates in the electric repulsion between colliding particles. Depending on its charge state, dust material may have the potential to control key processes towards planet formation such as magnetohydrodynamic (MHD) turbulence and grain growth, which are coupled in a two-way process. Aims: We quantify the grain charging at different stages of disc evolution and differentiate between two very extreme cases: compact spherical grains and aggregates with fractal dimension Df = 2. Methods: Applying a simple chemical network that accounts for collisional charging of grains, we provide a semi-analytical solution. This allowed us to calculate the equilibrium population of grain charges and the ionisation fraction efficiently. The grain charging was evaluated for different dynamical environments ranging from static to non-stationary disc configurations. Results: The results show that the adsorption/desorption of neutral gas-phase heavy metals, such as magnesium, effects the charging state of grains. The greater the difference between the thermal velocities of the metal and the dominant molecular ion, the greater the change in the mean grain charge. Agglomerates have more negative excess charge on average than compact spherical particles of the same mass. The rise in the mean grain charge is proportional to N1/6 in the ion-dust limit. We find that grain charging in a non-stationary disc environment is expected to lead to similar results. Conclusions: The results indicate that the dust growth and settling in regions where the dust growth is limited by the so-called "electro-static barrier" do not prevent the dust material from remaining the dominant charge carrier.

  2. Rehabilitation after lumbar disc surgery.

    PubMed

    Ostelo, R W; de Vet, H C; Waddell, G; Kerckhoffs, M R; Leffers, P; van Tulder, M W

    2002-01-01

    Although several rehabilitation programs, physical fitness programs or protocols regarding instruction for patients to return to work after lumbar disc surgery have been suggested, little is known about the efficacy and effectiveness of these treatments. There are still persistent fears of causing re-injury, re-herniation, or instability. The objective of this systematic review was to evaluate the effectiveness of active treatments that are used in the rehabilitation after first-time lumbar disc surgery. We searched the MEDLINE, EMBASE and Psyclit databases up to April 2000 and the Cochrane Controlled Trials Register 2001, Issue 3. Both randomized and non-randomized controlled trials on any type of active rehabilitation program after first-time disc surgery were included. Two independent reviewers performed the inclusion of studies and two other reviewers independently performed the methodological quality assessment. A rating system that consists of four levels of scientific evidence summarizes the results. Thirteen studies were included, six of which were of high quality. There is no strong evidence for the effectiveness for any treatment starting immediately post-surgery, mainly because of lack of (good quality) studies. For treatments that start four to six weeks post-surgery there is strong evidence (level 1) that intensive exercise programs are more effective on functional status and faster return to work (short-term follow-up) as compared to mild exercise programs and there is strong evidence (level 1) that on long term follow up there is no difference between intensive exercise programs and mild exercise programs with regard to overall improvement. For all other primary outcome measures for the comparison between intensive and mild exercise programs there is conflicting evidence (level 3) with regard to long-term follow-up. Furthermore, there is no strong evidence for the effectiveness of supervised training as compared to home exercises. There was also no

  3. Revival of the Jumping Disc

    ERIC Educational Resources Information Center

    Ucke, C.; Schlichting, H-J.

    2009-01-01

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

  4. The Chemistry of Optical Discs.

    ERIC Educational Resources Information Center

    Birkett, David

    2002-01-01

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

  5. Revival of the Jumping Disc

    ERIC Educational Resources Information Center

    Ucke, C.; Schlichting, H-J.

    2009-01-01

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

  6. How do accretion discs break?

    NASA Astrophysics Data System (ADS)

    Dogan, Suzan

    2016-07-01

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

  7. The DISC Quotient

    NASA Astrophysics Data System (ADS)

    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.

  8. Herniated Lumbar Disc

    MedlinePlus

    ... at and just below the waist. A herniated lumbar disc can press on the nerves in the spine and may cause pain, numbness, ... point injections do not help heal a herniated lumbar ... on and irritating the nerves, causing symptoms of pain and weakness. The most ...

  9. The Teddy Bears' Disc.

    ERIC Educational Resources Information Center

    Laurillard, Diana

    1985-01-01

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

  10. Hybrid cervical disc arthroplasty.

    PubMed

    Tu, Tsung-Hsi; Wu, Jau-Ching; Cheng, Henrich; Mummaneni, Praveen V

    2017-01-01

    For patients with multilevel cervical stenosis at nonadjacent segments, one of the traditional approaches has included a multilevel fusion of the abnormal segments as well as the intervening normal segment. In this video we demonstrate an alternative treatment plan with tailored use of a combination of anterior cervical discectomy and fusion (ACDF) and cervical disc arthroplasty (CDA) with an intervening skipped level. The authors present the case of a 72-year-old woman with myeloradiculopathy and a large disc herniation with facet joint degeneration at C3-4 and bulging disc at C5-6. After nonoperative treatment failed, she underwent a single-level ACDF at C3-4 and single-level arthroplasty at C5-6, which successfully relieved her symptoms. No intervention was performed at the normal intervening C4-5 segment. By using ACDF combined with arthroplasty, the authors have avoided a 3-level fusion for this patient and maintained the range of motion of 2 disc levels. The video can be found here: https://youtu.be/OrxcPUBvqLk .

  11. The Teddy Bears' Disc.

    ERIC Educational Resources Information Center

    Laurillard, Diana

    1985-01-01

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

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

    PubMed

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

    2013-05-24

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

  13. Partial Torus Instability

    NASA Astrophysics Data System (ADS)

    Olmedo, Oscar; Zhang, J.

    2010-05-01

    Flux ropes are now generally accepted to be the magnetic configuration of Coronal Mass Ejections (CMEs), which may be formed prior or during solar eruptions. In this study, we model the flux rope as a current-carrying partial torus loop with its two footpoints anchored in the photosphere, and investigate its instability in the context of the torus instability (TI). Previous studies on TI have focused on the configuration of a circular torus and revealed the existence of a critical decay index. Our study reveals that the critical index is a function of the fractional number of the partial torus, defined by the ratio between the arc length of the partial torus above the photosphere and the circumference of a circular torus of equal radius. We refer to this finding the partial torus instability (PTI). It is found that a partial torus with a smaller fractional number has a smaller critical index, thus requiring a more gradually decreasing magnetic field to stabilize the flux rope. On the other hand, the partial torus with a larger fractional number has a larger critical index. In the limit of a circular torus when the fractional number approaches one, the critical index goes to a maximum value that depends on the distribution of the external magnetic field. We demonstrate that the partial torus instability helps us to understand the confinement, growth, and eventual eruption of a flux rope CME.

  14. Electromagnetic ion beam instabilities

    NASA Technical Reports Server (NTRS)

    Gary, S. P.; Foosland, D. W.; Smith, C. W.; Lee, M. A.; Goldstein, M. L.

    1984-01-01

    The linear theory of electromagnetic instabilities driven by an energetic ion beam streaming parallel to a magnetic field in a homogeneous Vlasov plasma is considered. Numerical solutions of the full dispersion equation are presented. At propagation parallel to the magnetic field, there are four distinct instabilities. A sufficiently energetic beam gives rise to two unstable modes with right-hand polarization, one resonant with the beam, the other nonresonant. A beam with sufficiently large T (perpendicular to B)/T (parallel to B) gives rise to the left-hand ion cyclotron anisotropy instability at relatively small beam velocities, and a sufficiently hot beam drives unstable a left-hand beam resonant mode. The parametric dependences of the growth rates for the three high beam velocity instabilities are presented here. In addition, some properties at oblique propagation are examined. It is demonstrated that, as the beam drift velocity is increased, relative maxima in growth rates can arise at harmonics of the ion cyclotron resonance for both right and left elliptically polarized modes.

  15. Stable neutral atom trap with a thin superconducting disc.

    PubMed

    Shimizu, Fujio; Hufnagel, Christoph; Mukai, Tetsuya

    2009-12-18

    A stable magnetic quadrupole trap for neutral atoms on a superconducting Nb thin-film disc is demonstrated. The quadrupole field is composed of the magnetic field that is generated by vortices on the disc introduced by cooling the disc across the transition temperature with a finite field and an oppositely directed uniform field applied after cooling. The trap is stable when all trapping processes are performed above the dendritic instability temperature T(a). When the field intensity is changed below this temperature, the quadrupole field collapses and the trap disappears. The initial vortex density decreases even when the external field is changed at a temperature T > T(a). However, the vortex density is stabilized at an equilibrium density, whereas at T < T(a), it almost completely disappears. A stable trap can be formed, even when the initial vortices are introduced through a dendritic avalanche.

  16. Thin accretion discs are stabilized by a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Sądowski, Aleksander

    2016-07-01

    By studying three-dimensional, radiative, global simulations of sub-Eddington, geometrically thin (H/R ≈ 0.15) black hole accretion flows we show that thin discs which are dominated by magnetic pressure are stable against thermal instability. Such discs are thicker than predicted by the standard model and show significant amount of dissipation inside the marginally stable orbit. Radiation released in this region, however, does not escape to infinity but is advected into the black hole. We find that the resulting accretion efficiency (5.5 ± 0.5 per cent for the simulated 0.8dot{M}_Edd disc) is very close to the predicted by the standard model (5.7 per cent).

  17. Advancing the cellular and molecular therapy for intervertebral disc disease.

    PubMed

    Sakai, Daisuke; Grad, Sibylle

    2015-04-01

    The healthy intervertebral disc (IVD) fulfils the essential function of load absorption, while maintaining multi-axial flexibility of the spine. The interrelated tissues of the IVD, the annulus fibrosus, the nucleus pulposus, and the cartilaginous endplate, are characterised by their specific niche, implying avascularity, hypoxia, acidic environment, low nutrition, and low cellularity. Anabolic and catabolic factors balance a slow physiological turnover of extracellular matrix synthesis and breakdown. Deviations in mechanical load, nutrient supply, cellular activity, matrix composition and metabolism may initiate a cascade ultimately leading to tissue dehydration, fibrosis, nerve and vessel ingrowth, disc height loss and disc herniation. Spinal instability, inflammation and neural sensitisation are sources of back pain, a worldwide leading burden that is challenging to cure. In this review, advances in cell and molecular therapy, including mobilisation and activation of endogenous progenitor cells, progenitor cell homing, and targeted delivery of cells, genes, or bioactive factors are discussed.

  18. Spirals, gaps, cavities, gapities: What do planets do in discs?

    NASA Astrophysics Data System (ADS)

    Crida, A.

    2016-12-01

    In this presentation, part of the "Observations of discs" workshop, I address the theoretical point of view of planet-disc interactions. In section 2, I will review the physics of spirals, and explain why the inner and the outer wake created by a planet in a gaseous keplerian disc look very different, but their shape is independant of the mass of the planet and almost only depends on the aspect ratio of the disc. In the third section, I discuss the axisymmetric features (gaps and cavities), and how they differ in the gas or the dust component. However, to start with, some clarification of the nomenclature seems to be required, as observers and theorists may have a different idea of what a gap is. The definition of a "gapity" may help to clarify the situation of pre-transitional discs.

  19. Magnetohydrodynamic instability

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Cargill, P.; Forbes, T. G.; Hood, A. W.; Steinolfson, R. S.

    1986-01-01

    There have been major advances in the theory of magnetic reconnection and of magnetic instability, with important implications for the observations, as follows: (1) Fast and slow magnetic shock waves are produced by the magnetohydrodynamics of reconnection and are potential particle accelerators. (2) The impulsive bursty regime of reconnection gives a rapid release of magnetic energy in a series of bursts. (3) The radiative tearing mode creates cool filamentary structures in the reconnection process. (4) The stability analyses imply that an arcade can become unstable when either its height or twist of plasma pressure become too great.

  20. 26 CFR 1.6011-2 - Returns, etc., of DISC's and former DISC's.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 26 Internal Revenue 13 2011-04-01 2011-04-01 false Returns, etc., of DISC's and former DISC's. 1...., of DISC's and former DISC's. (a) Records and information. Every DISC and former DISC (as defined in..., statements, and special returns. Thus, for example, a DISC is required to maintain the books of account or...

  1. Evidence from stellar rotation of enhanced disc dispersal. I. The case of the triple visual system BD-21 1074 in the β Pictoris association

    NASA Astrophysics Data System (ADS)

    Messina, S.; Monard, B.; Biazzo, K.; Melo, C. H. F.; Frasca, A.

    2014-10-01

    Context. The early stage of stellar evolution is characterized by a magnetic coupling between a star and its accretion disc, known as a star-disc locking mechanism. The disc-locking prevents the star to spin its rotation up, and its timescale depends on the disc lifetime, which should not be longer than about 10 Myr. Some mechanisms can significantly shorten this lifetime, allowing a few stars to start spinning up much earlier than other stars and increasing the observed rotation period dispersion among coeval stars. Aims: In the present study, we aim to investigate how the properties of the circumstellar environment can shorten the disc lifetime, more specifically the presence of a close stellar companion. Methods: We have identified a few multiple stellar systems, composed of stars with similar masses, which belong to associations with a known age. Since all parameters that are responsible for the rotational evolution, with the exception of environment properties and initial stellar rotation, are similar for all components, we expect that significant differences among the rotation periods can only arise from differences in the disc lifetimes. A photometric timeseries allowed us to measure the rotation periods of each component, while high-resolution spectra provided us with the fundamental parameters, v sin i and chromospheric line fluxes. Results: In the present study, we have collected timeseries photometry of BD-21 1074, a member of the 21 Myr old β Pictoris association, and measured the rotation periods of its brightest components A and B. They differ significantly, and the component B, which has a closer companion C, rotates faster than the more distant and isolated component A. It also displays a slightly higher chromospheric activity level. Conclusions: Since components A and B have similar mass, age, and initial chemical composition, we can ascribe the rotation period difference to either different initial rotation periods or different disc

  2. Pad-mode-induced instantaneous mode instability for simple models of brake systems

    NASA Astrophysics Data System (ADS)

    Oberst, S.; Lai, J. C. S.

    2015-10-01

    Automotive disc brake squeal is fugitive, transient and remains difficult to predict. In particular, instantaneous mode squeal observed experimentally does not seem to be associated with mode coupling and its mechanism is not clear. The effects of contact pressures, friction coefficients as well as material properties (pressure and temperature dependency and anisotropy) for brake squeal propensity have not been systematically explored. By analysing a finite element model of an isotropic pad sliding on a plate similar to that of a previously reported experimental study, pad modes have been identified and found to be stable using conventional complex eigenvalue analysis. However, by subjecting the model to contact pressure harmonic excitation for a range of pressures and friction coefficients, a forced response analysis reveals that the dissipated energy for pad modes is negative and becomes more negative with increasing contact pressures and friction coefficients, indicating the potential for instabilities. The frequency of the pad mode in the sliding direction is within the range of squeal frequencies observed experimentally. Nonlinear time series analysis of the vibration velocity also confirms the evolution of instabilities induced by pad modes as the friction coefficient increases. By extending this analysis to a more realistic but simple brake model in the form of a pad-on-disc system, in-plane pad-modes, which a complex eigenvalue analysis predicts to be stable, have also been identified by negative dissipated energy for both isotropic and anisotropic pad material properties. The influence of contact pressures on potential instabilities has been found to be more dominant than changes in material properties owing to changes in pressure or temperature. Results here suggest that instantaneous mode squeal is likely caused by in-plane pad-mode instabilities.

  3. Dynamical and chemical evolution of the thin disc

    NASA Astrophysics Data System (ADS)

    Just, A.; Rybizki, J.

    2016-09-01

    Our detailed analytic local disc model (JJ-model) quantifies the interrelation between kinematic properties (e.g. velocity dispersions and asymmetric drift), spatial parameters (scale-lengths and vertical density profiles), and properties of stellar sub-populations (age and abundance distributions). Any consistent radial extension of the disc evolution model should predict specific features in the different distribution functions and in their correlations. Large spectroscopic surveys (SEGUE, RAVE, APOGEE, Gaia-ESO) allow significant constraints on the long-term evolution of the thin disc. We discuss the qualitative difference of correlations (like the α-enhancement as function of metallicity) and distribution functions (e.g. in [Mg/H] or [Fe/H]) for the construction of a disc model. In the framework of the JJ-model we build a local chemical enrichment model and show that significant vertical gradients for main sequence and red clump stars are expected in the thin disc. A Jeans analysis of the asymmetric drift provides a link to the radial structure of the disc. The derived metallicity-dependent radial scale-lengths can be combined in the future with the abundance distributions at different Galactocentric distances to construct full disc models. We expect to be able to constrain possible scenarios of inside-out growth of the thin disc and to characterise those populations, which require significant radial migration.

  4. Evidence for an Important Role of Smad-7 in Intervertebral Disc Degeneration

    PubMed Central

    Li, Bo; Su, Yi-Jun; Zheng, Xin-Feng; Yang, Yue-Hua; Jiang, Sheng-Dan

    2015-01-01

    Smad-7 inhibited the transforming growth factor beta (TGF-β)-induced proteoglycan synthesis in chondrocytes and completely antagonized the effect of TGF-β on the proliferation of the cells. The aim of this study was to evaluate the contribution of Smad-7 to the pathophysiology of disc degeneration by determining the expression of Smad-7 in the degenerative intervertebral discs and its effect on the extracellular matrix metabolism of disc cells. Instability of the lumbar spine produced by imbalanced dynamic and static forces was used to induce intervertebral disc degeneration in rats. The expression of Smad-7 was assessed by the immunohistochemical method. Disc cell apoptosis was detected by in situ TUNEL staining. The effect of Smad-7 overexpression on the matrix metabolism of disc cells was analyzed in vitro by real-time polymerase chain reaction (PCR) and Western blotting. Finally, intradiscal injection of the Smad-7 overexpression lentivirus was performed to evaluate the in vivo effect of Smad-7 on disc degeneration. Radiographic and histomorphological examinations showed that lumbar disc degeneration became more and more severe in the rats with induced instability. Immunohistochemical observation demonstrated increasing protein expression of Smad-7 in the degenerative discs. A significantly positive correlation was found between Smad-7 expression and the degree of disc degeneration and between Smad-7 expression and disc cell apoptosis. Overexpression of Smad-7 in disc cells inhibited the expression of TGF-β1, collagen type-I, collagen type-II, and aggrecan and promoted the expression of MMP-13, but did not change the expression of ADAMTS-5. The in vivo findings illustrated that intradiscal injection of lentivirus vector with Smad-7 overexpression accelerated the progress of disc degeneration. In conclusion, Smad-7 was highly expressed in the degenerative discs. Overexpression of Smad-7 weakened the protective role of TGF-β and accelerated the progress of

  5. Cytotoxicity-dependent APO-1 (Fas/CD95)-associated proteins form a death-inducing signaling complex (DISC) with the receptor.

    PubMed

    Kischkel, F C; Hellbardt, S; Behrmann, I; Germer, M; Pawlita, M; Krammer, P H; Peter, M E

    1995-11-15

    APO-1 (Fas/CD95), a member of the tumor necrosis factor receptor superfamily, induces apoptosis upon receptor oligomerization. In a search to identify intracellular signaling molecules coupling to oligomerized APO-1, several cytotoxicity-dependent APO-1-associated proteins (CAP) were immunoprecipitated from the apoptosis-sensitive human leukemic T cell line HUT78 and the lymphoblastoid B cell line SKW6.4. CAP1-3 (27-29 kDa) and CAP4 (55 kDa), instantly detectable after the crosslinking of APO-1, were associated only with aggregated (the signaling form of APO-1) and not with monomeric APO-1. CAP1 and CAP2 were identified as serine phosphorylated MORT1/FADD. The association of CAP1-4 with APO-1 was not observed with C-terminally truncated non-signaling APO-1. In addition, CAP1 and CAP2 did not associate with an APO-1 cytoplasmic tail carrying the lprcg amino acid replacement. Moreover, no APO-1-CAP association was found in the APO-1+, anti-APO-1-resistant pre-B cell line Boe. Our data suggest that in vivo CAP1-4 are the APO-1 apoptosis-transducing molecules.

  6. LUMBAR DISC HERNIATION

    PubMed Central

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

    2015-01-01

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

  7. Mechanotransduction in intervertebral discs

    PubMed Central

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

    2014-01-01

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

  8. Total disc replacement.

    PubMed

    Vital, J-M; Boissière, L

    2014-02-01

    Total disc replacement (TDR) (partial disc replacement will not be described) has been used in the lumbar spine since the 1980s, and more recently in the cervical spine. Although the biomechanical concepts are the same and both are inserted through an anterior approach, lumbar TDR is conventionally indicated for chronic low back pain, whereas cervical TDR is used for soft discal hernia resulting in cervicobrachial neuralgia. The insertion technique must be rigorous, with precise centering in the disc space, taking account of vascular anatomy, which is more complex in the lumbar region, particularly proximally to L5-S1. All of the numerous studies, including prospective randomized comparative trials, have demonstrated non-inferiority to fusion, or even short-term superiority regarding speed of improvement. The main implant-related complication is bridging heterotopic ossification with resulting loss of range of motion and increased rates of adjacent segment degeneration, although with an incidence lower than after arthrodesis. A sufficiently long follow-up, which has not yet been reached, will be necessary to establish definitively an advantage for TDR, particularly in the cervical spine. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

  9. Secular evolution of eccentricity in protoplanetary discs with gap-opening planets

    NASA Astrophysics Data System (ADS)

    Teyssandier, Jean; Ogilvie, Gordon I.

    2017-06-01

    We explore the evolution of the eccentricity of an accretion disc perturbed by an embedded planet whose mass is sufficient to open a large gap in the disc. Various methods for representing the orbit-averaged motion of an eccentric disc are discussed. We characterize the linear instability that leads to the growth of eccentricity by means of hydrodynamical simulations. We numerically recover the known result that eccentricity growth in the disc is possible when the planet-to-star mass ratio exceeds 3 × 10-3. For mass ratios larger than this threshold, the precession rates and growth rates derived from simulations, as well as the shape of the eccentric mode, compare well with the predictions of a linear theory of eccentric discs. We study mechanisms by which the eccentricity growth eventually saturates into a non-linear regime.

  10. Factors to be Considered for Selection and Design of Rupture Disc

    SciTech Connect

    Murty, D.V.R.; Bhaskar Rao, Y.; Chennakeshava Reddy, A.

    2006-07-01

    All over the world numerous fatalities and large property losses have taken place because of Industrial Explosions. In order to mitigate the losses of life and property due to overpressure rupture discs are used. Successful implementation would depend on many factors and one of the important factors is the selection and design of rupture discs. There are several factors that affect the disc performance. The present paper discusses the factors that effect the disc performance so that the right type of disc can be selected. (authors)

  11. Mechanics of Actuated Disc Cutting

    NASA Astrophysics Data System (ADS)

    Dehkhoda, Sevda; Detournay, Emmanuel

    2017-02-01

    This paper investigates the mechanics of an actuated disc cutter with the objective of determining the average forces acting on the disc as a function of the parameters characterizing its motion. The specific problem considered is that of a disc cutter revolving off-centrically at constant angular velocity around a secondary axis rigidly attached to a cartridge, which is moving at constant velocity and undercutting rock at a constant depth. This model represents an idealization of a technology that has been implemented in a number of hard rock mechanical excavators with the goal of reducing the average thrust force to be provided by the excavation equipment. By assuming perfect conformance of the rock with the actuated disc as well as a prescribed motion of the disc (perfectly rigid machine), the evolution of the contact surface between the disc and the rock during one actuation of the disc can be computed. Coupled with simple cutter/rock interaction models that embody either a ductile or a brittle mode of fragmentation, these kinematical considerations lead to an estimate of the average force on the cartridge and of the partitioning of the energy imparted by the disc to the rock between the actuation mechanism of the disc and the translation of the cartridge on which the actuated disc is attached.

  12. Estrogens and the intervertebral disc.

    PubMed

    Calleja-Agius, J; Muscat-Baron, Y; Brincat, M P

    2009-09-01

    Intervertebral discs are an integral part of the vertebral column. It has been shown that menopause has a negative effect on bone and on intervertebral discs. Estrogen has a beneficial effect of preserving the health of collagen-containing tissues, including the intervertebral disc. The intervertebral disc allows for mobility of the spine, and maintains a uniform stress distribution of the area of the vertebral endplates. Also, the disc influences spinal height. The disc tissue is adapted for this biomechanical function. The function of the spine is impaired if there is a loss of disc tissue. Narrowing of the disc space due to degeneration of intervertebral discs is associated with a significantly increased risk of vertebral fractures. Estrogen should be seen as the first-choice therapy for bones and other collagen-rich tissues, such as intervertebral discs, because it maintains homeostasis of the bone-remodelling unit. Unlike bisphosphonates, estrogen is unique in its ability to regenerate bone collagen after its disintegration, apart from suppressing osteoclastic activity. Besides, there is insufficient data on deterioration in bone qualities and micro-cracks in patients on long-term bisphosphonates.

  13. Polarimetric microlensing of circumstellar discs

    NASA Astrophysics Data System (ADS)

    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.

  14. Collisional dust avalanches in debris discs

    NASA Astrophysics Data System (ADS)

    Grigorieva, A.; Artymowicz, P.; Thébault, Ph.

    2007-01-01

    We quantitatively investigate how collisional avalanches may develop in debris discs as the result of the initial breakup of a planetesimal or comet-like object, triggering a collisional chain reaction due to outward escaping small dust grains. We use a specifically developed numerical code that follows both the spatial distribution of the dust grains and the evolution of their size-frequency distribution due to collisions. We investigate how strongly avalanche propagation depends on different parameters (e.g., amount of dust released in the initial breakup, collisional properties of dust grains, and their distribution in the disc). Our simulations show that avalanches evolve on timescales of ~1000 years, propagating outwards following a spiral-like pattern, and that their amplitude exponentially depends on the number density of dust grains in the system. We estimate the probability of witnessing an avalanche event as a function of disc densities, for a gas-free case around an A-type star, and find that features created by avalanche propagation can lead to observable asymmetries for dusty systems with a β Pictoris-like dust content or higher. Characteristic observable features include: (i) a brightness asymmetry of the two sides for a disc viewed edge-on, and (ii) a one-armed open spiral or a lumpy structure in the case of face-on orientation. A possible system in which avalanche-induced structures might have been observed is the edge-on seen debris disc around HD 32297, which displays a strong luminosity difference between its two sides.

  15. Accretion disk evolution in dwarf novae through outbursts: disk instability and mass-transfer instability cases

    NASA Astrophysics Data System (ADS)

    Baptista, R.

    I discuss a set of observations of eclipsing dwarf novae through outbursts which allow fundamental tests of the predictions of the two models proposed to explain their outbursts. The observational picture which emerges from these tests indicate that there are two distinct groups of dwarf novae. While the outbursts of one group can be understood in the framework of the thermal-viscous disc instability model, those of the other group can only be explained in terms of the mass-transfer instability model. I also show that morphological differences in the orbital light curves of eclipsing dwarf novae can be useful to distinguish members of each group.

  16. Rossby Wave Instability in Astrophysical Disks

    NASA Astrophysics Data System (ADS)

    Lovelace, Richard; Li, Hui

    2014-10-01

    A brief review is given of the Rossby wave instability in astrophysical disks. In non-self-gravitating discs, around for example a newly forming stars, the instability can be triggered by an axisymmetric bump at some radius r0 in the disk surface mass-density. It gives rise to exponentially growing non-axisymmetric perturbation (proportional to Exp[im ϕ], m = 1,2,...) in the vicinity of r0 consisting of anticyclonic vortices. These vortices are regions of high pressure and consequently act to trap dust particles which in turn can facilitate planetesimal growth in protoplanetary disks. The Rossby vortices in the disks around stars and black holes may cause the observed quasi-periodic modulations of the disk's thermal emission. Stirling Colgate's long standing interest in all types of vortices - particularly tornados - had an important part in stimulating the research on the Rossby wave instability.

  17. Gas Modelling in the Disc of HD 163296

    NASA Technical Reports Server (NTRS)

    Tilling, I.; Woitke, P.; Meeus, G.; Mora, A.; Montesinos, B.; Riviere-Marichalar, P.; Eiroa, C.; Thi, W. -F.; Isella, A.; Roberge, A.; Martin-Zaidi, C.; Kamp, I.; Pinte, C.; Sandell, G.; Vacca, W. D.; Menard, F.; Mendigutia, I.; Duchene, G.; Dent, W. R. F.; Aresu, G.; Meijerink, R.; Spaans, M.

    2011-01-01

    We present detailed model fits to observations of the disc around the Herbig Ae star HD 163296. This well-studied object has an age of approx. 4Myr, with evidence of a circumstellar disc extending out to approx. 540AU. We use the radiation thermo-chemical disc code ProDiMo to model the gas and dust in the circumstellar disc of HD 163296, and attempt to determine the disc properties by fitting to observational line and continuum data. These include new Herschel/PACS observations obtained as part of the open-time key program GASPS (Gas in Protoplanetary Systems), consisting of a detection of the [Oi] 63 m line and upper limits for several other far infrared lines. We complement this with continuum data and ground-based observations of the CO-12 3-2, 2-1 and CO-13 J=1-0 line transitions, as well as the H2 S(1) transition. We explore the effects of stellar ultraviolet variability and dust settling on the line emission, and on the derived disc properties. Our fitting efforts lead to derived gas/dust ratios in the range 9-100, depending on the assumptions made. We note that the line fluxes are sensitive in general to the degree of dust settling in the disc, with an increase in line flux for settled models. This is most pronounced in lines which are formed in the warm gas in the inner disc, but the low excitation molecular lines are also affected. This has serious implications for attempts to derive the disc gas mass from line observations. We derive fractional PAH abundances between 0.007 and 0.04 relative to ISM levels. Using a stellar and UV excess input spectrum based on a detailed analysis of observations, we find that the all observations are consistent with the previously assumed disc geometry

  18. Pattern Generation by Dissipative Parametric Instability.

    PubMed

    Perego, A M; Tarasov, N; Churkin, D V; Turitsyn, S K; Staliunas, K

    2016-01-15

    Nonlinear instabilities are responsible for spontaneous pattern formation in a vast number of natural and engineered systems, ranging from biology to galaxy buildup. We propose a new instability mechanism leading to pattern formation in spatially extended nonlinear systems, which is based on a periodic antiphase modulation of spectrally dependent losses arranged in a zigzag way: an effective filtering is imposed at symmetrically located wave numbers k and -k in alternating order. The properties of the dissipative parametric instability differ from the features of both key classical concepts of modulation instabilities, i.e., the Benjamin-Feir instability and the Faraday instabiltyity. We demonstrate how the dissipative parametric instability can lead to the formation of stable patterns in one- and two-dimensional systems. The proposed instability mechanism is generic and can naturally occur or can be implemented in various physical systems.

  19. Pattern Generation by Dissipative Parametric Instability

    NASA Astrophysics Data System (ADS)

    Perego, A. M.; Tarasov, N.; Churkin, D. V.; Turitsyn, S. K.; Staliunas, K.

    2016-01-01

    Nonlinear instabilities are responsible for spontaneous pattern formation in a vast number of natural and engineered systems, ranging from biology to galaxy buildup. We propose a new instability mechanism leading to pattern formation in spatially extended nonlinear systems, which is based on a periodic antiphase modulation of spectrally dependent losses arranged in a zigzag way: an effective filtering is imposed at symmetrically located wave numbers k and -k in alternating order. The properties of the dissipative parametric instability differ from the features of both key classical concepts of modulation instabilities, i.e., the Benjamin-Feir instability and the Faraday instabiltyity. We demonstrate how the dissipative parametric instability can lead to the formation of stable patterns in one- and two-dimensional systems. The proposed instability mechanism is generic and can naturally occur or can be implemented in various physical systems.

  20. Kinetic theory of Jeans instability.

    PubMed

    Trigger, S A; Ershkovich, A I; van Heijst, G J F; Schram, P P J M

    2004-06-01

    Kinetic treatment of the Jeans gravitational instability, with collisions taken into account, is presented. The initial-value problem for the distribution function which obeys the kinetic equation, with the collision integral conserving the number of particles, is solved. Dispersion relation is obtained and analyzed. New modes are found. Collisions are shown not to affect the Jeans instability criterion. Although the instability growth rate diminishes, the collisions they cannot quench the instability. However, the oscillation spectrum is modified significantly: even in the neighborhood of the threshold frequency omega=0 (separating stable and unstable modes) the spectrum of oscillations can strongly depend on the collision frequency. Propagating (rather than aperiodic) modes are also found. These modes, however, are strongly damped.

  1. Structural Raman enhancement in graphite nano-discs

    NASA Astrophysics Data System (ADS)

    Cardenas, J. F.; Chakarov, D.; Kasemo, B.

    2016-04-01

    Raman scattering in disc-shaped graphite nanostructures, etched out of bulk HOPG, are investigated using an excitation wavelength of 532 nm at different laser power. The G-band is fitted using two Lorentzian functions, GL and GH. The difference of Raman shift between the two Lorentzian functions increase with laser power as a consequence of selective absorption and heating of the discs. Further, the G-band from the nanostructured HOPG reveal a Raman enhancement (RE) of ~2.2 and ~1.5 for the components associated with the discs (GL) and the supporting substrate (GH), respectively. The quantitative agreement between the experimental results and performed finite difference time domain calculations make possible to conclude that electromagnetic energy penetrates considerably into the discs from the circular periphery probably due to multiple scattering. In addition, the dependence of RE of the GL component on the laser power is attributed to a temperature dependent electron-phonon coupling.

  2. Enclosed rotary disc air pulser

    DOEpatents

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

    1989-01-01

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

  3. Heat distribution in disc brake

    NASA Astrophysics Data System (ADS)

    Klimenda, Frantisek; Soukup, Josef; Kampo, Jan

    2016-06-01

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

  4. Size-dependent snap-through and pull-in instabilities of initially curved pre-stressed electrostatic nano-bridges

    NASA Astrophysics Data System (ADS)

    Shojaeian, Milad; Tadi Beni, Yaghoub; Ataei, Hossein

    2016-07-01

    This study investigates the electromechanical instabilities of micro/nanobeams with initial curved shape and subjected to electrostatic field and Casimir intermolecular force. Using modified couple stress theory and the principle of minimum potential energy and variational approach, the nonlinear equations associated with boundary conditions are derived. The generalized differential quadrature (GDQ) method is used to discretize the equations and boundary conditions, and then the discretized form of equations are solved numerically. In the end, the impacts of fringing field effect, beam imperfection and size effect on microbeam are investigated and the results are compared with experimental results. Besides, in the end the effect of Casimir intermolecular force in initially curved nanobeams and its symmetric and asymmetric effects on snap-through and pull-in instabilities are discussed.

  5. Chicken granulosa cells show differential expression of epidermal growth factor (EGF) and luteinizing hormone (LH) receptor messenger RNA and differential responsiveness to EGF and LH dependent upon location of granulosa cells to the germinal disc.

    PubMed

    Yao, H H; Bahr, J M

    2001-06-01

    Granulosa cells in the chicken follicle exhibit different phenotypes according to their location relative to the germinal disc (GD). Granulosa cells proximal to the GD (referred to as proximal granulosa cells) are more proliferative, whereas granulosa cells distal to the GD (referred to as distal granulosa cells) are more differentiated. We have shown that epidermal growth factor (EGF) derived from the GD stimulated proliferation of granulosa cells proximal to the GD, whereas extraovarian LH promoted differentiation. We tested the hypothesis that phenotypic differences of granulosa cells are the result of differential responsiveness of granulosa cells to EGF and LH. We found that both granulosa and theca layers of chicken preovulatory follicles expressed mRNA for EGF receptor (EGFr) by polymerase chain reaction (PCR) analysis. However, only the granulosa layer showed differential expression of EGFr and LH receptor (LHr) mRNA. Competitive reverse transcription-PCR revealed that proximal granulosa cells expressed more EGFr mRNA but less LHr mRNA than distal granulosa cells. In addition, proximal granulosa cells proliferated more in response to EGF than their distal counterparts. We further demonstrated that EGF decreased LHr mRNA expression by granulosa cells in a dose-dependent manner, whereas EGF and LH had no effect on EGFr mRNA expression except at one dose of LH (15 ng/ml) that stimulated EGFr mRNA expression. Our findings suggest that EGF derived from the GD influences the phenotypes of granulosa cells. Granulosa cells proximal to the GD exhibit a proliferative phenotype possibly because they are exposed to and are more responsive to GD-derived EGF. Furthermore, GD-derived EGF decreases LHr mRNA expression by proximal granulosa cells and therefore results in less differentiated granulosa cell phenotype. In contrast, granulosa cells distal to the GD are not under the influence of EGF and exhibit a more differentiated phenotype.

  6. Cutting Frozen Ground with Disc Saws

    DTIC Science & Technology

    1975-06-01

    a (actor ot 5. taking a depth widtli ratio toi the uncut nbs ol 2. Axle torces on the cutter wheel depend on the design ol the cutting teeth and on...position. If the shoulder of the cutting tool behind the cutting edge is exactly tangential, it will grind against uncut material and...AD-A012 114 CUTTING FROZEN GROUND UITH DISC SAWS Mai colm Mel lor Cold Regions Research and Engineering Laboratory Hanover, New

  7. Investigating the Magnetorotational Instability with Dedalus, and Open-Souce Hydrodynamics Code

    SciTech Connect

    Burns, Keaton J; /UC, Berkeley, aff SLAC

    2012-08-31

    The magnetorotational instability is a fluid instability that causes the onset of turbulence in discs with poloidal magnetic fields. It is believed to be an important mechanism in the physics of accretion discs, namely in its ability to transport angular momentum outward. A similar instability arising in systems with a helical magnetic field may be easier to produce in laboratory experiments using liquid sodium, but the applicability of this phenomenon to astrophysical discs is unclear. To explore and compare the properties of these standard and helical magnetorotational instabilities (MRI and HRMI, respectively), magnetohydrodynamic (MHD) capabilities were added to Dedalus, an open-source hydrodynamics simulator. Dedalus is a Python-based pseudospectral code that uses external libraries and parallelization with the goal of achieving speeds competitive with codes implemented in lower-level languages. This paper will outline the MHD equations as implemented in Dedalus, the steps taken to improve the performance of the code, and the status of MRI investigations using Dedalus.

  8. Numbered nasal discs for waterfowl

    USGS Publications Warehouse

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

    1964-01-01

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

  9. Accretion does not drive the turbulence in galactic discs

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.; Kereš, Dušan; Murray, Norman

    2013-07-01

    Rapid accretion of cold intergalactic gas plays a crucial role in getting gas into galaxies. It has been suggested that this gas accretion proceeds along narrow streams that might also directly drive the turbulence in galactic gas, dynamical disturbances and bulge formation. In cosmological simulations, however, it is impossible to isolate and hence disentangle the effect of cold stream accretion from internal instabilities and mergers. Moreover, in most current cosmological simulations, the phase structure and turbulence in the interstellar medium (ISM) arising from stellar feedback are treated in an approximate (subgrid) manner, so that the feedback cannot generate turbulence in the ISM. In this paper we therefore test the effects of cold streams in extremely high-resolution simulations of otherwise isolated galaxy discs using detailed models for star formation and stellar feedback; we then include or exclude mock cold flows falling on to the galaxies, with mass accretion rates, velocities and flow geometry set to maximize their effect on the gaseous disc. We find (1) turbulent velocity dispersions in gas discs are identical with or without the presence of the cold flow; the energy injected by the flow is efficiently dissipated where it meets the disc. (2) In runs without stellar feedback, the presence of a cold flow has essentially no effect on runaway fragmentation (local collapse), resulting in star formation rates (SFRs) that are an order-of-magnitude too large. (3) Model discs in runs with both explicit feedback and cold flows have higher SFRs, but only insofar as they have more gas. (4) Because the flows are extended, relative to the size of the disc, they do not trigger strong resonant responses and so induce weak gross morphological perturbation (bulge formation via instabilities/fragmentation is not accelerated). (5) However, flows can thicken the disc by direct contribution of out-of-plane or misaligned star-forming streams/filaments. We conclude that

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  11. Magnetothermal instability with generalized Ohm's law

    SciTech Connect

    Bora, M.P.; Talwar, S.P. )

    1993-03-01

    The problem of thermal instability, having bearing on the formation of astrophysical condensations, is investigated for a hydromagnetic fluid obeying generalized Ohm's law, both for self-gravitating and nongravitating configurations. Effects of finite Larmor frequency, resistivity, and finite plasma frequency on the stability of the system are studied and the condition of instabilities are derived for a temperature-dependent and density-dependent heat-loss function. It is found that the condition of instability for propagation parallel to the ambient magnetic field is independent of finite resistivity, Hall current, and electron inertia effects and also of the magnetic field strength. For transverse propagation, however, the instability criterion involves the field strength, resistivity, and electron inertia terms. The Hall current is found to modify the growth rates for generally inclined propagation only. Both monotonically unstable and overstable modes of instability arise in the system depending on the dependence of the heat-loss function on the local density and temperature.

  12. [Temporomandibular joint disc surgery].

    PubMed

    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.

  13. Polygonal instabilities

    NASA Astrophysics Data System (ADS)

    Labousse, Matthieu

    2015-11-01

    The interaction of a vortex with a free surface is encountered in a series of experiments, the hydraulic jump, the hydraulic bump, the toroidal Leidenfrost experiment. All these experiments share in common an unstable configuration in which azimuthal perturbations give rise to polygonal patterns. We propose a unified theoretical framework to model the emergence of this instability by investigating the stability of a liquid torus with a poloidal motion. As simple as it is, we show that the model retains the necessary ingredients to account for the experimental observations. In this talk, I will first describe the model and compare it to the existing data. However this model is purely inviscid and reaches its limits when being applied to relatively moderate Reynolds flows. So in a second part, I will present a recent experimental and theoretical investigation in which polygonal patterns are now driven by Marangoni flows. To our great surprise, it extends the range of validity of the initial proposed framework, much more than initially expected.

  14. 26 CFR 1.6011-2 - Returns, etc., of DISC's and former DISC's.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 13 2010-04-01 2010-04-01 false Returns, etc., of DISC's and former DISC's. 1... (CONTINUED) INCOME TAX (CONTINUED) INCOME TAXES Tax Returns Or Statements § 1.6011-2 Returns, etc., of DISC's and former DISC's. (a) Records and information. Every DISC and former DISC (as defined in section 992...

  15. Simulations of magnetic fields in isolated disc galaxies

    NASA Astrophysics Data System (ADS)

    Pakmor, Rüdiger; Springel, Volker

    2013-06-01

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

  16. The matrikine N-acetylated proline-glycine-proline induces premature senescence of nucleus pulposus cells via CXCR1-dependent ROS accumulation and DNA damage and reinforces the destructive effect of these cells on homeostasis of intervertebral discs.

    PubMed

    Feng, Chencheng; Zhang, Yang; Yang, Minghui; Lan, Minghong; Liu, Huan; Wang, Jian; Zhou, Yue; Huang, Bo

    2017-01-01

    Intervertebral disc (IVD) cell senescence is a recognized mechanism of intervertebral disc degeneration (IDD). Elucidating the molecular mechanisms underlying disc cell senescence will contribute to understanding the pathogenesis of IDD. We previously reported that N-acetylated proline-glycine-proline (N-Ac-PGP), a matrikine, is involved in the process of IDD. However, its roles in IDD are not well understood. Here, using rat nucleus pulposus (NP) cells, we found that N-Ac-PGP induced premature senescence of NP cells by binding to CXCR1. N-Ac-PGP induced DNA damage and reactive oxygen species accumulation in NP cells, which resulted in activation of the p53-p21-Rb and p16-Rb pathways. Moreover, the RT(2) profiler PCR array showed that N-Ac-PGP down-regulates the expression of antioxidant genes in NP cells, suggesting a decline in the antioxidants of NP cells. On the other hand, N-Ac-PGP up-regulated the expression of matrix catabolic genes and inflammatory genes in NP cells. Concomitantly, N-Ac-PGP reinforced the destructive effects of senescent NP cells on the homeostasis of the IVDs in vivo. Our study suggests that N-Ac-PGP plays critical roles in the pathogenesis of IDD through the induction of premature senescence of disc cells and via the activation of catabolic and inflammatory cascades in disc cells. N-Ac-PGP also deteriorates the redox environment of disc cells. Hence, N-Ac-PGP is a new potential therapeutic target for IDD.

  17. Preparation of ormetoprim sulfadimethoxine medicated discs for disc diffusion assay

    USDA-ARS?s Scientific Manuscript database

    Romet (a blend of ormetoprim and sulfadimethoxine) is a typeA medicated article for the manufacture of medicated feed in the catfish industry. Recently, the commercial manufacture of ormetoprim–sulfadimethoxine susceptibility discs was discontinued. Ormetoprim–sulfadimethoxine discs were prepared at...

  18. Miniaturized Lab-on-a-Disc (miniLOAD).

    PubMed

    Glass, Nick R; Shilton, Richie J; Chan, Peggy P Y; Friend, James R; Yeo, Leslie Y

    2012-06-25

    A miniaturized centrifugal microfluidic platform for lab-on-a-chip applications is presented. Unlike its macroscopic Lab-on-a-CD counterpart, the miniature Lab-on-a-Disc (miniLOAD) device does not require moving parts to drive rotation of the disc, is inexpensive, disposable, and significantly smaller, comprising a 10-mm-diameter SU-8 disc fabricated through two-step photolithography. The disc is driven to rotate using surface acoustic wave irradiation incident upon a fluid coupling layer from a pair of offset, opposing single-phase unidirectional transducers patterned on a lithium niobate substrate. The irradiation causes azimuthally oriented acoustic streaming with sufficient intensity to rotate the disc at several thousand revolutions per minute. In this first proof-of-concept, the capability of the miniLOAD platform to drive capillary-based valving and mixing in microfluidic structures on a disc similar to much larger Lab-on-a-CD devices is shown. In addition, the ability to concentrate aqueous particle suspensions at radial positions in a channel in the disc dependent on the particles' size is demonstrated. To the best of our knowledge, the miniLOAD concept is the first centrifugal microfluidic platform small enough to be self-contained in a handheld device.

  19. Disc cell therapies: critical issues.

    PubMed

    Tibiletti, Marta; Kregar Velikonja, Nevenka; Urban, Jill P G; Fairbank, Jeremy C T

    2014-06-01

    Disc cell therapies, in which cells are injected into the degenerate disc in order to regenerate the matrix and restore function, appear to be an attractive, minimally invasive method of treatment. Interest in this area has stimulated research into disc cell biology in particular. However, other important issues, some of which are discussed here, need to be considered if cell-based therapies are to be brought to the clinic. Firstly, a question which is barely addressed in the literature, is how to identify patients with 'degenerative disc disease' who would benefit from cell therapy. Pain not disc degeneration is the symptom which drives patients to the clinic. Even though there are associations between back pain and disc degeneration, many people with even severely degenerate discs, with herniated discs or with spinal stenosis, are pain-free. It is not possible using currently available techniques to identify whether disc repair or regeneration would remove symptoms or prevent symptoms from occurring in future. Moreover, the repair process in human discs is very slow (years) because of the low cell density which can be supported nutritionally even in healthy human discs. If repair is necessary for relief of symptoms, questions regarding quality of life and rehabilitation during this long process need consideration. Also, some serious technical issues remain. Finding appropriate cell sources and scaffolds have received most attention, but these are not the only issues determining the feasibility of the procedure. There are questions regarding the safety of implanting cells by injection through the annulus whether the nutrient supply to the disc is sufficient to support implanted cells and whether, if cells are able to survive, conditions in a degenerate human disc will allow them to repair the damaged tissue. If cell therapy for treatment of disc-related disorders is to enter the clinic as a routine treatment, investigations must examine the questions related to

  20. Fantastic Disc Activities for Fitness

    ERIC Educational Resources Information Center

    Griffin, Michael R.; Johnson, Romona; Thomas, Jessica; Spell, Melissa; Popham, John; Croft, Brent; Umpleby, Albert; Verbel, Eric

    2005-01-01

    Disc activities are an excellent elementary content area for both skill and fitness enhancement. They may occur through progressive skill and drill practice, small sided-game examples, modifications of traditional disc activities appropriate to large groups, and with adjustments designed to increase activity and fitness levels. For games in this…

  1. Stellar explosions, instabilities, and turbulence

    SciTech Connect

    Drake, R. P.; Kuranz, C. C.; Miles, A. R.; Muthsam, H. J.; Plewa, T.

    2009-04-15

    It has become very clear that the evolution of structure during supernovae is centrally dependent on the pre-existing structure in the star. Modeling of the pre-existing structure has advanced significantly, leading to improved understanding and to a physically based assessment of the structure that will be present when a star explodes. It remains an open question whether low-mode asymmetries in the explosion process can produce the observed effects or whether the explosion mechanism somehow produces jets of material. In any event, the workhorse processes that produce structure in an exploding star are blast-wave driven instabilities. Laboratory experiments have explored these blast-wave-driven instabilities and specifically their dependence on initial conditions. Theoretical work has shown that the relative importance of Richtmyer-Meshkov and Rayleigh-Taylor instabilities varies with the initial conditions and does so in ways that can make sense of a range of astrophysical observations.

  2. On the interaction of stationary crossflow vortices and Tollmien-Schlichting waves in the boundary layer on a rotating disc

    NASA Technical Reports Server (NTRS)

    Bassom, Andrew P.; Hall, Philip

    1989-01-01

    There are many fluid flows where the onset of transition can be caused by different instability mechanisms which compete among themselves. The interaction is considered of two types of instability mode (at an asymptotically large Reynolds number) which can occur in the flow above a rotating disc. In particular, the interaction is examined between lower branch Tollmien-Schlichting (TS) waves and the upper branch, stationary, inviscid crossflow vortex whose asymptotic structure has been described by Hall (1986). This problem is studied in the context of investigating the effect of the vortex on the stability characteristics of a small TS wave. Essentially, it is found that the primary effect is felt through the modification to the mean flow induced by the presence of the vortex. Initially, the TS wave is taken to be linear in character and it is shown (for the cases of both a linear and a nonlinear stationary vortex) that the vortex can exhibit both stabilizing and destabilizing effects on the TS wave and the nature of this influence is wholly dependent upon the orientation of this latter instability. Further, the problem is examined with a larger TS wave, whose size is chosen so as to ensure that this mode is nonlinear in its own right. An amplitude equation for the evolution of the TS wave is derived which admits solutions corresponding to finite amplitude, stable, traveling waves.

  3. Radiofrequency stimulation of intervertebral discs.

    PubMed

    Rosen, Steven; Falco, Frank

    2003-10-01

    The etiology of discogenic pain is poorly understood. The most accepted theory has been that nociceptors in the outer one-third of the annulus fibrosis are responsible for transmitting pain secondary to internal disc disruptions. The concept of "neoneuralization" after disc injury has been disseminated. It has been noted that disc degeneration and injury are associated with ingrowth of neural fibers into the disc annulus. One mechanism of Intradiscal Electrodothermal Therapy (IDET) has been thought to be lesioning of these nociceptors. Five consecutive patients were studied using an intraannular electrode. The Radionics discTRODE was used. It was found impossible to selectively stimulate axial pain fibers using this system. Radicular stimulation was noted in all patients at all levels studied. The implication of these findings concerning the concept of neoneuralization, mechanism of IDET, and possible strategies to decrease discogenic pain are discussed.

  4. Imaginal disc regeneration takes flight.

    PubMed

    Hariharan, Iswar K; Serras, Florenci

    2017-04-01

    Drosophila imaginal discs, the larval precursors of adult structures such as the wing and leg, are capable of regenerating after damage. During the course of regeneration, discs can sometimes generate structures that are appropriate for a different type of disc, a phenomenon termed transdetermination. Until recently, these phenomena were studied by physically fragmenting discs and then transplanting them into the abdomens of adult female flies. This field has experienced a renaissance following the development of genetic ablation systems that can damage precisely defined regions of the disc without the need for surgery. Together with more traditional approaches, these newer methods have generated many novel insights into wound healing, the mechanisms that drive regenerative growth, plasticity during regeneration and systemic effects of tissue damage and regeneration.

  5. A truly Newtonian softening length for disc simulations

    NASA Astrophysics Data System (ADS)

    Huré, J.-M.; Trova, A.

    2015-02-01

    The softened point mass model is commonly used in simulations of gaseous discs including self-gravity while the value of associated length λ remains, to some degree, controversial. This `parameter' is however fully constrained when, in a discretized disc, all fluid cells are demanded to obey Newton's law. We examine the topology of solutions in this context, focusing on cylindrical cells more or less vertically elongated. We find that not only the nominal length depends critically on the cell's shape (curvature, radial extension, height), but it is either a real or an imaginary number. Setting λ as a fraction of the local disc thickness - as usually done - is indeed not the optimal choice. We then propose a novel prescription valid irrespective of the disc properties and grid spacings. The benefit, which amounts to 2-3 more digits typically, is illustrated in a few concrete cases. A detailed mathematical analysis is in progress.

  6. Thalamic Pain Misdiagnosed as Cervical Disc Herniation.

    PubMed

    Lim, Tae Ha; Choi, Soo Il; Yoo, Jee In; Choi, Young Soon; Lim, Young Su; Sang, Bo Hyun; Bang, Yun Sic; Kim, Young Uk

    2016-04-01

    Thalamic pain is a primary cause of central post-stroke pain (CPSP). Clinical symptoms vary depending on the location of the infarction and frequently accompany several pain symptoms. Therefore, correct diagnosis and proper examination are not easy. We report a case of CPSP due to a left acute thalamic infarction with central disc protrusion at C5-6. A 45-year-old-male patient experiencing a tingling sensation in his right arm was referred to our pain clinic under the diagnosis of cervical disc herniation. This patient also complained of right cramp-like abdominal pain. After further evaluations, he was diagnosed with an acute thalamic infarction. Therefore detailed history taking should be performed and examiners should always be aware of other symptoms that could suggest a more dangerous disease.

  7. Intraoral micro-identification discs.

    PubMed

    Hansen, R W

    1991-12-01

    Intraoral micro-identification discs have recently been utilized to provide a more permanent method of personal identification. A wafer of plastic or metal with a surface area of 2.5 to 5 mm2 and carrying identifying numbers and/or letters (indicia) is bonded to the buccal enamel surface of the posterior teeth. Personal identification can occur after the I.D. disc is identified and the indicia is read. Reading of photoreduced indicia requires the aid of a microscope subsequent to the removal of the microdisc. In situ reading of disc indicia is possible using low power handheld magnifiers if the size of the indicia approximates 0.3 mm. Computerization is an integral part of non-custom alpha/numeric type designs, but a custom disc carries a name, address, and other specific information unique to the manufacturer. The use of a computer improves access to the database and it decreases the amount of data placed on the disc. Microdisc bases may be fabricated using a mylar type plastic or they may be manufactured from a stainless steel blank. Plastic discs are constructed with an internal sandwich containing the photo-reduced indicia. Metal discs are marked with a photochemical etch or engraved with a computer driven YAG laser. Attachment of the disc to the enamel surface is accomplished by conventional etching and bonding techniques and are typically bonded to the buccal surface of the maxillary first permanent molar or the second primary molar. Clear composite bonding material covers the disc so that salivary contamination does not result in degradation of the indicia. Orthodontic style discs with a mesh back carry laser written information that may be cemented with conventional orthodontic bonding cement. Standardization of the indicia and overall design is considered to be an important aspect of patient and professional acceptance.

  8. In vitro and in silico investigations of disc nucleus replacement

    PubMed Central

    Reitmaier, Sandra; Shirazi-Adl, Aboulfazl; Bashkuev, Maxim; Wilke, Hans-Joachim; Gloria, Antonio; Schmidt, Hendrik

    2012-01-01

    Currently, numerous hydrogels are under examination as potential nucleus replacements. The clinical success, however, depends on how well the mechanical function of the host structure is restored. This study aimed to evaluate the extent to and mechanisms by which surgery for nucleus replacements influence the mechanical behaviour of the disc. The effects of an annulus defect with and without nucleus replacement on disc height and nucleus pressure were measured using 24 ovine motion segments. The following cases were considered: intact; annulus incision repaired by suture and glue; annulus incision with removal and re-implantation of nucleus tissue repaired by suture and glue or plug. To identify the likely mechanisms observed in vitro, a finite-element model of a human disc (L4–L5) was employed. Both studies were subjected to physiological cycles of compression and recovery. A repaired annulus defect did not influence the disc behaviour in vitro, whereas additional nucleus removal and replacement substantially decreased disc stiffness and nucleus pressure. Model predictions demonstrated the substantial effects of reductions in replaced nucleus water content, bulk modulus and osmotic potential on disc height loss and pressure, similar to measurements. In these events, the compression load transfer in the disc markedly altered by substantially increasing the load on the annulus when compared with the nucleus. The success of hydrogels for nucleus replacements is not only dependent on the implant material itself but also on the restoration of the environment perturbed during surgery. The substantial effects on the disc response of disruptions owing to nucleus replacements can be simulated by reduced nucleus water content, elastic modulus and osmotic potential. PMID:22337630

  9. Observational signatures of linear warps in circumbinary discs

    NASA Astrophysics Data System (ADS)

    Juhász, Attila; Facchini, Stefano

    2017-04-01

    In recent years, an increasing number of observational studies have hinted at the presence of warps in protoplanetary discs; however, a general comprehensive description of observational diagnostics of warped discs was missing. We performed a series of 3D smoothed particle hydrodynamic simulations and combined them with 3D radiative transfer calculations to study the observability of warps in circumbinary discs, whose plane is misaligned with respect to the orbital plane of the central binary. Our numerical hydrodynamic simulations confirm previous analytical results on the dependence of the warp structure on the viscosity and the initial misalignment between the binary and the disc. To study the observational signatures of warps, we calculate images in the continuum at near-infrared and submillimetre wavelengths and in the pure rotational transition of CO in the submillimetre. Warped circumbinary discs show surface brightness asymmetry in near-infrared scattered light images as well as in optically thick gas lines at submillimetre wavelengths. The asymmetry is caused by self-shadowing of the disc by the inner warped regions, thus the strength of the asymmetry depends on the strength of the warp. The projected velocity field, derived from line observations, shows characteristic deviations, twists and a change in the slope of the rotation curve, from that of an unperturbed disc. In extreme cases even the direction of rotation appears to change in the disc inwards of a characteristic radius. The strength of the kinematical signatures of warps decreases with increasing inclination. The strength of all warp signatures decreases with decreasing viscosity.

  10. Observational signatures of linear warps in circumbinary discs

    NASA Astrophysics Data System (ADS)

    Juhász, Attila; Facchini, Stefano

    2017-01-01

    In recent years an increasing number of observational studies have hinted at the presence of warps in protoplanetary discs, however a general comprehensive description of observational diagnostics of warped discs was missing. We performed a series of 3D SPH hydrodynamic simulations and combined them with 3D radiative transfer calculations to study the observability of warps in circumbinary discs, whose plane is misaligned with respect to the orbital plane of the central binary. Our numerical hydrodynamic simulations confirm previous analytical results on the dependence of the warp structure on the viscosity and the initial misalignment between the binary and the disc. To study the observational signatures of warps we calculate images in the continuum at near-infrared and sub-millimetre wavelengths and in the pure rotational transition of CO in the sub-millimetre. Warped circumbinary discs show surface brightness asymmetry in near-infrared scattered light images as well as in optically thick gas lines at sub-millimetre wavelengths. The asymmetry is caused by self-shadowing of the disc by the inner warped regions, thus the strength of the asymmetry depends on the strength of the warp. The projected velocity field, derived from line observations, shows characteristic deviations, twists and a change in the slope of the rotation curve, from that of an unperturbed disc. In extreme cases even the direction of rotation appears to change in the disc inwards of a characteristic radius. The strength of the kinematical signatures of warps decreases with increasing inclination. The strength of all warp signatures decreases with decreasing viscosity.

  11. In vitro and in silico investigations of disc nucleus replacement.

    PubMed

    Reitmaier, Sandra; Shirazi-Adl, Aboulfazl; Bashkuev, Maxim; Wilke, Hans-Joachim; Gloria, Antonio; Schmidt, Hendrik

    2012-08-07

    Currently, numerous hydrogels are under examination as potential nucleus replacements. The clinical success, however, depends on how well the mechanical function of the host structure is restored. This study aimed to evaluate the extent to and mechanisms by which surgery for nucleus replacements influence the mechanical behaviour of the disc. The effects of an annulus defect with and without nucleus replacement on disc height and nucleus pressure were measured using 24 ovine motion segments. The following cases were considered: intact; annulus incision repaired by suture and glue; annulus incision with removal and re-implantation of nucleus tissue repaired by suture and glue or plug. To identify the likely mechanisms observed in vitro, a finite-element model of a human disc (L4-L5) was employed. Both studies were subjected to physiological cycles of compression and recovery. A repaired annulus defect did not influence the disc behaviour in vitro, whereas additional nucleus removal and replacement substantially decreased disc stiffness and nucleus pressure. Model predictions demonstrated the substantial effects of reductions in replaced nucleus water content, bulk modulus and osmotic potential on disc height loss and pressure, similar to measurements. In these events, the compression load transfer in the disc markedly altered by substantially increasing the load on the annulus when compared with the nucleus. The success of hydrogels for nucleus replacements is not only dependent on the implant material itself but also on the restoration of the environment perturbed during surgery. The substantial effects on the disc response of disruptions owing to nucleus replacements can be simulated by reduced nucleus water content, elastic modulus and osmotic potential.

  12. Mode-locking via dissipative Faraday instability.

    PubMed

    Tarasov, Nikita; Perego, Auro M; Churkin, Dmitry V; Staliunas, Kestutis; Turitsyn, Sergei K

    2016-08-09

    Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin-Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system-spectrally dependent losses-achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin-Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering.

  13. Mode-locking via dissipative Faraday instability

    PubMed Central

    Tarasov, Nikita; Perego, Auro M.; Churkin, Dmitry V.; Staliunas, Kestutis; Turitsyn, Sergei K.

    2016-01-01

    Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin–Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system—spectrally dependent losses—achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin–Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering. PMID:27503708

  14. Mode-locking via dissipative Faraday instability

    NASA Astrophysics Data System (ADS)

    Tarasov, Nikita; Perego, Auro M.; Churkin, Dmitry V.; Staliunas, Kestutis; Turitsyn, Sergei K.

    2016-08-01

    Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin-Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system--spectrally dependent losses--achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin-Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering.

  15. Cervical Total Disc Arthroplasty

    PubMed Central

    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 arthroplasty devices have come onto the market and completed Food and Drug Administration Investigational Device Exemption trials. Though some of the early results demonstrate equivalency of arthroplasty to fusion, compelling evidence of benefits in terms of symptomatic adjacent segment degeneration are lacking. In addition, non-industry-sponsored studies indicate that these devices are equivalent to fusion in terms of adjacent segment degeneration. Longer-term studies will eventually provide the definitive answer. PMID:24353955

  16. Disc hemorrhages and treatment in the early manifest glaucoma trial.

    PubMed

    Bengtsson, Boel; Leske, M Cristina; Yang, Zhongming; Heijl, Anders

    2008-11-01

    To evaluate the effect of intraocular pressure (IOP)-reducing treatment on the development of disc hemorrhages in patients with glaucoma. Prospective cohort study of patients in the Early Manifest Glaucoma Trial, followed up to 11 years (median = 8 years). Patients with newly detected glaucoma randomized to argon laser trabeculoplasty plus betaxolol (n = 129) or no initial treatment (n = 126), followed with tonometry, perimetry, and ophthalmoscopy every 3 months, and fundus photography every 6 months. Logistic regression expressed as odds ratios (OR) and 95% confidence intervals (CIs), analysis of variance, and Cox time-dependent models, expressed as hazard ratios (HRs) and CIs. Presence (yes/no) and frequency of disc hemorrhages. Disc hemorrhages were identified in approximately 55% of all patients, whether by ophthalmoscopy or review of photographs. In analyses including data up to the time of progression, disc hemorrhages were equally common among treated and control patients: 51.2% versus 45.2%, respectively (P = 0.34), based on ophthalmoscopy, and 50.4% versus 44.4%, respectively (P = 0.34), based on photographs. Gender was the only factor related to the presence of disc hemorrhages detected by both ophthalmoscopy (OR = 0.48; CI, 0.26-0.88; P = 0.022) and photographs (OR = 0.64; CI, 0.38-1.09; P = 0.099) for male patients. The frequency of disc hemorrhages over time did not differ between treated and control patients: 8.4% versus 8.5%, respectively (P = 0.93), based on ophthalmoscopy, and 12.4% versus 11.2%, respectively (P = 0.36), based on photographs. Disc hemorrhages were significantly associated with time to progression (HR = 1.02; CI, 1.01-1.04), and there was no evidence of interaction between treatment group and disc hemorrhages. IOP-reducing treatment was unrelated to the presence or frequency of disc hemorrhages. The results may suggest that disc hemorrhages cannot be considered an indication of insufficient IOP-lowering treatment, and that glaucoma

  17. The growth of discs and bulges during hierarchical galaxy formation - II. Metallicity, stellar populations and dynamical evolution

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    We investigate the properties of the stellar populations of model galaxies as a function of galaxy evolutionary history and angular momentum content. We use the new semi-analytic model presented in Tonini et al. This new model follows the angular momentum evolution of gas and stars, providing the base for a new star formation recipe, and treatment of the effects of mergers that depends on the central galaxy dynamical structure. We find that the new recipes have the effect of boosting the efficiency of the baryonic cycle in producing and recycling metals, as well as preventing minor mergers from diluting the metallicity of bulges and ellipticals. The model reproduces the stellar mass-stellar metallicity relation for galaxies above 1010 solar masses, including Brightest Cluster Galaxies. Model discs, galaxies dominated by instability-driven components, and merger-driven objects each stem from different evolutionary channels. These model galaxies therefore occupy different loci in the galaxy mass-size relation, which we find to be in accord with the ATLAS 3D classification of disc galaxies, fast rotators and slow rotators. We find that the stellar populations' properties depend on the galaxy evolutionary type, with more evolved stellar populations being part of systems that have lost or dissipated more angular momentum during their assembly history.

  18. Magnetorotationally driven wind cycles in local disc models

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  19. Global stability of self-gravitating discs in modified gravity

    NASA Astrophysics Data System (ADS)

    Ghafourian, Neda; Roshan, Mahmood

    2017-07-01

    Using N-body simulations, we study the global stability of a self-gravitating disc in the context of modified gravity (MOG). This theory is a relativistic scalar-tensor-vector theory of gravity and it is presented to address the dark matter problem. In the weak field limit, MOG possesses two free parameters α and μ0, which have already been determined using the rotation curve data of spiral galaxies. The evolution of a stellar self-gravitating disc and, more specifically, the bar instability in MOG are investigated and compared to a Newtonian case. Our models have exponential and Mestel-like surface densities as Σ ∝ exp (-r/h) and Σ ∝ 1/r. It is found that, surprisingly, the discs are more stable against the bar mode in MOG than in Newtonian gravity. In other words, the bar growth rate is effectively slower than the Newtonian discs. Also, we show that both free parameters (i.e. α and μ0) have stabilizing effects. In other words, an increase in these parameters will decrease the bar growth rate.

  20. Double-disc gate valve

    DOEpatents

    Wheatley, Seth J.

    1979-01-01

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

  1. On the dynamic instability of nanowire-fabricated electromechanical actuators in the Casimir regime: Coupled effects of surface energy and size dependency

    NASA Astrophysics Data System (ADS)

    Keivani, Maryam; Mardaneh, Mohamadreza; Koochi, Ali; Rezaei, Morteza; Abadyan, Mohamadreza

    2016-02-01

    Herein, the dynamic pull-in instability of cantilever nanoactuator fabricated from conductive cylindrical nanowire with circular cross-section is studied under the presence of Casimir force. The Gurtin-Murdoch surface elasticity in combination with the couple stress theory is employed to incorporate the coupled effects of surface energy and size phenomenon. Using Green-Lagrange strain, the higher order surface stress components are incorporated in the governing equation. The Dirichlet mode is considered and an asymptotic solution, based on the path integral approach, is applied to consider the effect of the Casimir attraction. Furthermore, the influence of structural damping is considered in the model. The nonlinear governing equation is solved using analytical reduced order method (ROM). The effects of various parameters on the dynamic pull-in parameters, phase planes and stability threshold of the actuator are demonstrated.

  2. Stability of galactic discs: finite arm-inclination and finite-thickness effects

    NASA Astrophysics Data System (ADS)

    Griv, Evgeny; Gedalin, Michael

    2012-05-01

    A modified theory of the Lin-Shu density waves, studied in connection with the problem of spiral pattern of rapidly and differentially rotating disc galaxies, is presented for both the axisymmetric and non-axisymmetric structures in highly flattened galaxies resulted from the classical Jeans instability of small gravity perturbations (e.g. those produced by a spontaneous disturbance). A new method is provided for the analytical solution of the self-consistent system of the gas-dynamic equations and the Poisson equation describing the stability of a three-dimensional galactic disc composed of stars or gaseous clouds. In order to apply the method, the modifications introduced for the properties of the gravitationally unstable, that is to say, amplitude-growing density waves are considered by removing the often used assumptions that the gravity perturbations are axisymmetric and the disc is infinitesimally thin. In contrast to previous studies, in this paper these two effects - the non-axial symmetry effect and the finite thickness effect - are simultaneously taken into account. We show that non-axisymmetric perturbations developing in a differentially rotating disc are more unstable than the axisymmetric ones. We also show that destabilizing self-gravity is far more 'dangerous' in thin discs than in thick discs. The primary effect of small but finite thickness is a reduction of the growth rate of the gravitational Jeans instability and a shift in the threshold of instability towards a longer wavelength (and larger wavelength will include more mass). The results of this paper are in qualitative agreement with previous analytical and numerical estimations of the effects. The extent to which our results on the disc's stability can have a bearing on observable spiral galaxies, including the Milky Way, is also discussed.

  3. Mechanical Instabilities of Biological Tubes

    NASA Astrophysics Data System (ADS)

    Hannezo, Edouard; Prost, Jacques; Joanny, Jean-François

    2012-07-01

    We study theoretically the morphologies of biological tubes affected by various pathologies. When epithelial cells grow, the negative tension produced by their division provokes a buckling instability. Several shapes are investigated: varicose, dilated, sinuous, or sausagelike. They are all found in pathologies of tracheal, renal tubes, or arteries. The final shape depends crucially on the mechanical parameters of the tissues: Young’s modulus, wall-to-lumen ratio, homeostatic pressure. We argue that since tissues must be in quasistatic mechanical equilibrium, abnormal shapes convey information as to what causes the pathology. We calculate a phase diagram of tubular instabilities which could be a helpful guide for investigating the underlying genetic regulation.

  4. Effect of nicotine on spinal disc cells: a cellular mechanism for disc degeneration.

    PubMed

    Akmal, Mohammed; Kesani, Anil; Anand, Bobby; Singh, Abhinav; Wiseman, Mike; Goodship, Allen

    2004-03-01

    Experimental investigation to determine the effect of nicotine on intervertebral spinal disc nucleus pulposus (NP) cells cultured in vitro. OBJECTIVES.: To evaluate the effects of nicotine on cell proliferation, extracellular matrix production, and viability of NP cells in three-dimensional alginate constructs cultured in vitro. Numerous studies confirm that smoking is a strong risk factor for back pain. The most widely accepted explanations for the association between smoking and disc degeneration is malnutrition of spinal disc cells by carboxy-hemoglobin-induced anoxia or vascular disease. Nicotine, a constituent of tobacco smoke, present in most body fluids of smokers is known to have detrimental effects on a variety of tissues. It may also be directly responsible for intervertebral disc (IVD) degeneration by causing cell damage in both the nucleus pulposus and anulus fibrosus. The effect of nicotine on IVD cells has not previously been investigated. Bovine chondrocytic intervertebral disc cells were isolated by sequential digestion of nucleus pulposus and seeded in 2% alginate. The constructs were cultured for 21 days either in growth medium containing freebase nicotine (Sigma) at concentrations found in the serum of smokers (25 nmol/L-300 nmol/L) or in standard nicotine free-medium as controls. Samples were collected at time points 3, 7, 14, and 21 days and a quantitative assay was performed for DNA, glycosaminoglycans (GAG), and hydroxyproline. Samples were also processed for qualitative histologic analysis including immunolocalization of collagen types I and II. There was both a dose- and time-dependent response to nicotine, with constructs cultured in low-nicotine concentration media demonstrating an early increase in DNA, GAG, and collagen content, while constructs cultured in high nicotine concentration media demonstrated a late decrease in these parameters. At 25 nmol/L dose of nicotine, there was a significant increase (P < 0.05) in the above parameters

  5. Mitral disc-valve variance

    PubMed Central

    Berroya, Renato B.; Escano, Fernando B.

    1972-01-01

    This report deals with a rare complication of disc-valve prosthesis in the mitral area. A significant disc poppet and struts destruction of mitral Beall valve prostheses occurred 20 and 17 months after implantation. The resulting valve incompetence in the first case contributed to the death of the patient. The durability of Teflon prosthetic valves appears to be in question and this type of valve probably will be unacceptable if there is an increasing number of disc-valve variance in the future. Images PMID:5017573

  6. Medical Information on Optical Disc*

    PubMed Central

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

    1987-01-01

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

  7. Quantifying the evolution of planetesimals embedded in magnetized protoplanetary discs with dead zones

    NASA Astrophysics Data System (ADS)

    Gressel, O.; Nelson, R. P.; Turner, N. J.

    2011-10-01

    Sufficiently ionized sections of protoplanetary discs are thought to be in a turbulent state powered by the magnetorotational instability (MRI). Previous work [1, 2] has shown that a swarm of planetesimals embedded in a fully turbulent disc is subject to strong excitation of its velocity dispersion, along with significant radial diffusion of semi-major axes. Implications include the collisional destruction of small bodies, and levels of large-scale spread of populations incompatible with the observed distribution within the asteroid belt. The picture remains unchanged when vertical stratification is included [3], and we suggest that planetesimal growth via mutual collisions cannot occur in a fully MRI-active disc. By contrast, a magnetically dead zone may provide a safe haven in which km-sized planetesimals can avoid mutual destruction [3]. First preliminary results from new simulations indicate that this finding also holds for increased disc masses, i.e., for more extended dead zones.

  8. Origin of structures in disc galaxies: internal or external processes?

    NASA Astrophysics Data System (ADS)

    Athanassoula, E.

    2015-03-01

    Disc galaxies have a number of structures, such as bars, spirals, rings, discy bulges, m = 1 asymmetries, thick discs, warps etc. I will summarise what is known about their origin and in particular whether it is due to an external or an internal process. The former include interactions, major or minor mergers etc, while the latter include instabilities, or driving by another component of the same galaxy, as e.g. the bar or the halo. In cases where more than one process is eligible, I will analyse whether it is possible to distinguish between different origins, and what it would take to do so. This discussion will show that, at least in some cases, it is difficult to distinguish between an internal and an external origin.

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

    PubMed

    Ogilvie, Gordon I

    2008-05-28

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

  10. A Novel Approach to the Surgical Treatment of Lumbar Disc Herniations: Indications of Simple Discectomy and Posterior Transpedicular Dynamic Stabilization Based on Carragee Classification

    PubMed Central

    Ozer, A. F.; Keskin, F.; Oktenoglu, T.; Suzer, T.; Ataker, Y.; Gomleksiz, C.; Sasani, M.

    2013-01-01

    Surgery of lumbar disc herniation is still a problem since Mixter and Barr. Main trouble is dissatisfaction after the operation. Today there is a debate on surgical or conservative treatment despite spending great effort to provide patients with satisfaction. The main problem is segmental instability, and the minimally invasive approach via microscope or endoscope is not necessarily appropriate solution for all cases. Microsurgery or endoscopy would be appropriate for the treatment of Carragee type I and type III herniations. On the other hand in Carragee type II and type IV herniations that are prone to develop recurrent disc herniation and segmental instability, the minimal invasive techniques might be insufficient to achieve satisfactory results. The posterior transpedicular dynamic stabilization method might be a good solution to prevent or diminish the recurrent disc herniation and development of segmental instability. In this study we present our experience in the surgical treatment of disc herniations. PMID:23653862

  11. Depth-dependent critical-current density of melt-processed Y-Ba-Cu-O discs determined by the third-harmonic technique: Surface barrier and intrinsic pinning

    NASA Astrophysics Data System (ADS)

    Chen, D.-X.; He, T.-F.; Zhang, M.-J.; Wang, S.-S.; Shi, Y.-H.; Cardwell, D. A.

    2016-08-01

    The critical-current density Jc of three Y-Ba-Cu-O (YBCO) discs, each cut from the upper section of a melt-processed single grain, has been determined as a function of the depth from the top (seeded) and bottom surfaces of the sample by a modified version of the inductive third-harmonic technique proposed originally by Mawatari et al. It is shown that local Jc in the vicinity of the bottom surface of the sample is lower than that in the vicinity of the top surface for thicker discs and there are reduced effect of surface barrier and intrinsic pinning and important surface damage. The technique employed is recommended as a tool for detecting the imperfection within superconducting structure in bulk YBCO.

  12. Electrothermal instability growth in magnetically driven pulsed power liners

    SciTech Connect

    Peterson, Kyle J.; Sinars, Daniel B.; Yu, Edmund P.; Herrmann, Mark C.; Cuneo, Michael E.; Slutz, Stephen A.; Smith, Ian C.; Atherton, Briggs W.; Knudson, Marcus D.; Nakhleh, Charles

    2012-09-15

    This paper explores the role of electro-thermal instabilities on the dynamics of magnetically accelerated implosion systems. Electro-thermal instabilities result from non-uniform heating due to temperature dependence in the conductivity of a material. Comparatively little is known about these types of instabilities compared to the well known Magneto-Rayleigh-Taylor (MRT) instability. We present simulations that show electrothermal instabilities form immediately after the surface material of a conductor melts and can act as a significant seed to subsequent MRT instability growth. We also present the results of several experiments performed on Sandia National Laboratories Z accelerator to investigate signatures of electrothermal instability growth on well characterized initially solid aluminum and copper rods driven with a 20 MA, 100 ns risetime current pulse. These experiments show excellent agreement with electrothermal instability simulations and exhibit larger instability growth than can be explained by MRT theory alone.

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

    PubMed Central

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

    2016-01-01

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

  14. Circumplanetary disc or circumplanetary envelope?

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  15. Enlivening Physics, a Local Video Disc Project.

    ERIC Educational Resources Information Center

    McInerney, M.

    1989-01-01

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

  16. 46 CFR 64.61 - Rupture disc.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 2 2010-10-01 2010-10-01 false Rupture disc. 64.61 Section 64.61 Shipping COAST GUARD... SYSTEMS Pressure Relief Devices and Vacuum Relief Devices for MPTs § 64.61 Rupture disc. If a rupture disc is the only pressure relief device on the tank, the rupture disc must— (a) Rupture at a pressure of...

  17. Disc Golf: Teaching a Lifetime Activity

    ERIC Educational Resources Information Center

    Eastham, Susan L.

    2015-01-01

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

  18. 46 CFR 64.61 - Rupture disc.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 2 2011-10-01 2011-10-01 false Rupture disc. 64.61 Section 64.61 Shipping COAST GUARD... SYSTEMS Pressure Relief Devices and Vacuum Relief Devices for MPTs § 64.61 Rupture disc. If a rupture disc is the only pressure relief device on the tank, the rupture disc must— (a) Rupture at a pressure of...

  19. Disc Golf: Teaching a Lifetime Activity

    ERIC Educational Resources Information Center

    Eastham, Susan L.

    2015-01-01

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

  20. Design Issues in Video Disc Map Display.

    DTIC Science & Technology

    1984-10-01

    Tables: disc storage capacities under various conditions. Photos: map frames. Constanzo , D.J. (1984a), "The Potential for Video Disc Technology in...discs. Constanzo , D.J. (1984b), "Requirements and Specifications for Cartographic Video Discs", presented as a poster paper at the 1984 Army Science

  1. Enlivening Physics, a Local Video Disc Project.

    ERIC Educational Resources Information Center

    McInerney, M.

    1989-01-01

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

  2. An opening criterion for dust gaps in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Dipierro, Giovanni; Laibe, Guillaume

    2017-08-01

    We aim to understand under which conditions a low-mass planet can open a gap in viscous dusty protoplanetary discs. For this purpose, we extend the theory of dust radial drift to include the contribution from the tides of an embedded planet and from the gas viscous forces. From this formalism, we derive (i) a grain-size-dependent criterion for dust gap opening in discs, (ii) an estimate of the location of the outer edge of the dust gap and (iii) an estimate of the minimum Stokes number above which low-mass planets are able to carve gaps that appear only in the dust disc. These analytical estimates are particularly helpful to appraise the minimum mass of a hypothetical planet carving gaps in discs observed at long wavelengths and high resolution. We validate the theory against 3D smoothed particle hydrodynamics simulations of planet-disc interaction in a broad range of dusty protoplanetary discs. We find a remarkable agreement between the theoretical model and the numerical experiments.

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

    NASA Astrophysics Data System (ADS)

    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. Electron heat flux instability

    NASA Astrophysics Data System (ADS)

    Saeed, Sundas; Sarfraz, M.; Yoon, P. H.; Lazar, M.; Qureshi, M. N. S.

    2017-02-01

    The heat flux instability is an electromagnetic mode excited by a relative drift between the protons and two-component core-halo electrons. The most prominent application may be in association with the solar wind where drifting electron velocity distributions are observed. The heat flux instability is somewhat analogous to the electrostatic Buneman or ion-acoustic instability driven by the net drift between the protons and bulk electrons, except that the heat flux instability operates in magnetized plasmas and possesses transverse electromagnetic polarization. The heat flux instability is also distinct from the electrostatic counterpart in that it requires two electron species with relative drifts with each other. In the literature, the heat flux instability is often called the 'whistler' heat flux instability, but it is actually polarized in the opposite sense to the whistler wave. This paper elucidates all of these fundamental plasma physical properties associated with the heat flux instability starting from a simple model, and gradually building up more complexity towards a solar wind-like distribution functions. It is found that the essential properties of the instability are already present in the cold counter-streaming electron model, and that the instability is absent if the protons are ignored. These instability characteristics are highly reminiscent of the electron firehose instability driven by excessive parallel temperature anisotropy, propagating in parallel direction with respect to the ambient magnetic field, except that the free energy source for the heat flux instability resides in the effective parallel pressure provided by the counter-streaming electrons.

  5. 26 CFR 1.246-4 - Dividends from a DISC or former DISC.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 26 Internal Revenue 3 2011-04-01 2011-04-01 false Dividends from a DISC or former DISC. 1.246-4... a DISC or former DISC. The deduction provided in section 243 (relating to dividends received by... distribution or an amount treated as a dividend pursuant to section 995(c)) from a corporation which is a DISC...

  6. Mass transfer between debris discs during close stellar encounters

    NASA Astrophysics Data System (ADS)

    Jílková, Lucie; Hamers, Adrian S.; Hammer, Michael; Portegies Zwart, Simon

    2016-04-01

    We study mass transfers between debris discs during stellar encounters. We carried out numerical simulations of close flybys of two stars, one of which has a disc of planetesimals represented by test particles. We explored the parameter space of the encounters, varying the mass ratio of the two stars, their pericentre and eccentricity of the encounter, and its geometry. We find that particles are transferred to the other star from a restricted radial range in the disc and the limiting radii of this transfer region depend on the parameters of the encounter. We derive an approximate analytic description of the inner radius of the region. The efficiency of the mass transfer generally decreases with increasing encounter pericentre and increasing mass of the star initially possessing the disc. Depending on the parameters of the encounter, the transfer particles have a specific distribution in the space of orbital elements (semimajor axis, eccentricity, inclination, and argument of pericentre) around their new host star. The population of the transferred particles can be used to constrain the encounter through which it was delivered. We expect that many stars experienced transfer among their debris discs and planetary systems in their birth environment. This mechanism presents a formation channel for objects on wide orbits of arbitrary inclinations, typically having high eccentricity but possibly also close to circular (eccentricities of about 0.1). Depending on the geometry, such orbital elements can be distinct from those of the objects formed around the star.

  7. EXPLOSIVE INSTABILITY AND CORONAL HEATING

    SciTech Connect

    Dahlburg, R. B.; Liu, J.-H.; Klimchuk, J. A.; Nigro, G.

    2009-10-20

    The observed energy-loss rate from the solar corona implies that the coronal magnetic field has a critical angle at which energy is released. It has been hypothesized that at this critical angle an 'explosive instability' would occur, leading to an enhanced conversion of magnetic energy into heat. In earlier investigations, we have shown that a shear-dependent magnetohydrodynamic process called 'secondary instability' has many of the distinctive features of the hypothetical 'explosive instability'. In this paper, we give the first demonstration that this 'secondary instability' occurs in a system with line-tied magnetic fields and boundary shearing-basically the situation described by Parker. We also show that, as the disturbance due to secondary instability attains finite amplitude, there is a transition to turbulence which leads to enhanced dissipation of magnetic and kinetic energy. These results are obtained from numerical simulations performed with a new parallelized, viscoresistive, three-dimensional code that solves the cold plasma equations. The code employs a Fourier collocation-finite difference spatial discretization, and uses a third-order Runge-Kutta temporal discretization.

  8. Sensitivity of the magnetorotational instability to the shear parameter in stratified simulations

    NASA Astrophysics Data System (ADS)

    Nauman, Farrukh; Blackman, Eric G.

    2015-01-01

    The magnetorotational instability (MRI) is a shear instability and thus its sensitivity to the shear parameter q = -d ln Ω/d ln r is of interest to investigate. Motivated by astrophysical discs, most (but not all) previous MRI studies have focused on the Keplerian value of q = 1.5. Using simulation with eight vertical density scaleheights, we contribute to the subset of studies addressing the effect of varying q in stratified numerical simulations. We discuss why shearing boxes cannot easily be used to study q > 2 and thus focus on q < 2. As per previous simulations, which were either unstratified or stratified with a smaller vertical domain, we find that the q dependence of stress for the stratified case is not linear, contrary to the Shakura-Sunyaev model. We find that the scaling agrees with Abramowicz, Brandenburg & Lasota who found it to be proportional to the shear to vorticity ratio q/(2 - q). We also find however that the shape of the magnetic and kinetic energy spectra are relatively insensitive to q and that the ratio of Maxwell stress to magnetic energy ratio also remains nearly independent of q. This is consistent with a theoretical argument in which the rate of amplification of the azimuthal field depends linearly on q and the turbulent correlation time τ depends inversely on q. As such, we measure the correlation time of the turbulence and find that indeed it is inversely proportional to q.

  9. Percutaneous cervical nucleoplasty in the treatment of cervical disc herniation

    PubMed Central

    Li, Jian; Zhang, Zai-Heng

    2008-01-01

    Percutaneous disc decompression procedures have been performed in the past. Various percutaneous techniques such as percutaneous discectomy, laser discectomy, and nucleoplasty have been successful. Our prospective study was directly to evaluate the results of percutaneous cervical nucleoplasty (PCN) surgery for cervical disc herniation, and illustrate the effectiveness of PCN in symptomatic patients who had cervical herniated discs. From July of 2002 to June of 2005, 126 consecutive patients with contained cervical disc herniations have presented at the authors’ clinic and treated by PCN. The patients’ gender distribution for PCN was 65 male, 61 female. The age of patients ranged from 34 to 66 years (mean 51.9 ± 10.2 years). The levels of involvement were 21 cases at C3–4, 30 cases at C4–5, 40 cases at C5–6, and 35 cases at C6–7. The clinical outcomes, pain reduction and the segment stability were all recorded during this study. A clinical outcome was quantified by the Macnab standard and using VAS. The angular displacement (AD) ≥11° or horizontal displacement (HD) ≥3 mm was considered to be radiographically unstable. In the results of this study, puncture of the needle into the disc space was accurately performed under X-ray guidance in all cases. There was one case where the Perc-D Spine Wand had broken in the disc space during the procedure. The partial Perc-D Spine Wand, which had broken in the disc space could not be removed by the percutaneous cervical discectomy and thus remained there. There were no recurrent cases or complications in our series. Macnab standard results were excellent in 62 cases, good in 41 cases and fair in 23 cases. The rate of excellent and good was 83.73%. The VAS scores demonstrated statistically significant improvement in PCN at the 2-week, 1, 3, 6, and 12-month follow-up visits when compared to preoperational values (P < 0.01). There were no cases of instability following the PCN procedure. There was no

  10. Tissue engineering: A live disc

    NASA Astrophysics Data System (ADS)

    Hukins, David W. L.

    2005-12-01

    A material-cell hybrid device that mimics the anatomic shape of the intervertebral disc has been made and successfully implanted into mice to show that tissue engineering may, in the future, benefit sufferers from back pain.

  11. Eclipse Mapping of Accretion Discs

    NASA Astrophysics Data System (ADS)

    Baptista, R.

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

  12. Kluger's "fixateur interne" for spinal instability.

    PubMed

    Sandvoss, G; Feldmann, H

    1991-01-01

    Kluger's "Fixateur Interne" proved to be an excellent tool not only in spinal trauma for repositioning of impacted fractures and transpedicular stabilization of the dorsal column but also in other forms of thoracic or lumbar instability. After spinal tumor excision from a dorsal approach and vertebral replacement with methylmethacrylate additional stability through dorsal fixation was achieved with this device. Spondylodiscitis, symptomatic spondylolisthesis, spinal instability from degenerative disc disease as well as "non-union" following previous surgery could be cured using Kluger's internal fixation. Rare complications, i.e. from broken screws or rods (5%) caused no problems, but some patients required a second operation for readjustment of malpositioned screws which were causing pain or neurological deficit.

  13. Disc Golf, a Growing Sport

    PubMed Central

    Nelson, Joseph T.; Jones, Richard E.; Runstrom, Michael; Hardy, Jolene

    2015-01-01

    Background Disc golf is a sport played much like traditional golf, but rather than using a ball and club, players throw flying discs with various throwing motions. It has been played by an estimated 8 to 12 million people in the United States. Like all sports, injuries sustained while playing disc golf are not uncommon. Although formalized in the 1970s, it has grown at a rapid pace; however, disc golf–related injuries have yet to be described in the medical literature. Purpose To describe the most common injuries incurred by disc golf players while comparing the different types of throwing styles. Study Design Descriptive epidemiology study. Methods The data in this study were collected from 883 disc golf players who responded to an online survey collected over a 1-month period. Respondents answered 49 questions related to demographics, experience, style of play, and injury details. Using a chi-square analysis, common injuries sustained in players using backhand and forehand throwing styles were compared. Results More than 81% of respondents stated that they had sustained an injury playing disc golf, including injuries to the elbow (n = 325), shoulder (n = 305), back (n = 218), and knee (n = 199). The injuries were most commonly described as a muscle strain (n = 241), sprain (n = 162), and tendinitis (n = 145). The type of throw primarily used by players varied, with 86.2% using backhand, 12.7% using forehand, and 1.1% using an overhead throw. Players using a forehand throw were more likely to sustain an elbow injury (P = .014). Many players (n = 115) stated they had undergone surgery due to a disc golf–related injury, with the most common surgeries including meniscal, shoulder, spine, and foot/ankle surgeries. Conclusion The majority of surveyed disc golfers sustained at least 1 injury while playing disc golf, with many requiring surgery. The types of injuries sustained by players varied by the types of throw primarily used. As the sport of disc golf continues

  14. On the behaviour of the magnetorotational instability when the Rayleigh criterion is violated

    NASA Astrophysics Data System (ADS)

    Balbus, Steven A.

    2012-06-01

    An elementary but revealing analysis of the dispersion relation of the magnetorotational instability (MRI) in the Ralyeigh-unstable regime is described. The defining properties of the MRI - its maximum growth rate and the direction of the associated eigenvector displacement - remain unchanged as the Rayleigh discriminant passes from positive to negative values. At sufficiently negative discriminant values, however, the spectrum of unstable modes becomes dominated by zero wavenumber disturbances, and the problem loses its local character. These results may be relevant to understanding the level of turbulent fluid stress near the innermost stable circular orbit (ISCO) in an accretion disc around a black hole, since the Rayleigh discriminant changes sign at this location. Our conclusions are consistent with numerical simulations that find finite stress at the ISCO, some dependence of the stress magnitude with scale height, and a plunging region much closer to the event horizon than the ISCO radius.

  15. Percutaneous diode laser disc nucleoplasty

    NASA Astrophysics Data System (ADS)

    Menchetti, P. P.; Longo, Leonardo

    2004-09-01

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

  16. Kinesics of Affective Instability.

    ERIC Educational Resources Information Center

    Dil, Nasim

    1979-01-01

    Discusses the rationale of studying kinesics of affective instability, describes the phenonmenon of affective instability, examines the role of kinesics in the overall process of communication, and presents three case studies. (Author/AM)

  17. Turbine instabilities: Case histories

    NASA Technical Reports Server (NTRS)

    Laws, C. W.

    1985-01-01

    Several possible causes of turbine rotor instability are discussed and the related design features of a wide range of turbomachinery types and sizes are considered. The instrumentation options available for detecting rotor instability and assessing its severity are also discussed.

  18. Effect of Size-Dependent Thermal Instability on Synthesis of Zn2SiO4-SiO x Core-Shell Nanotube Arrays and Their Cathodoluminescence Properties

    NASA Astrophysics Data System (ADS)

    Li, Chun; Bando, Yoshio; Dierre, Benjamin; Sekiguchi, Takashi; Huang, Yang; Lin, Jing; Golberg, Dmitri

    2010-04-01

    Vertically aligned Zn2SiO4-SiO x ( x < 2) core-shell nanotube arrays consisting of Zn2SiO4-nanoparticle chains encapsulated into SiO x nanotubes and SiO x -coated Zn2SiO4 coaxial nanotubes were synthesized via one-step thermal annealing process using ZnO nanowire (ZNW) arrays as templates. The appearance of different nanotube morphologies was due to size-dependent thermal instability and specific melting of ZNWs. With an increase in ZNW diameter, the formation mechanism changed from decomposition of “etching” to Rayleigh instability and then to Kirkendall effect, consequently resulting in polycrystalline Zn2SiO4-SiO x coaxial nanotubes, single-crystalline Zn2SiO4-nanoparticle-chain-embedded SiO x nanotubes, and single-crystalline Zn2SiO4-SiO x coaxial nanotubes. The difference in spatially resolved optical properties related to a particular morphology was efficiently documented by means of cathodoluminescence (CL) spectroscopy using a middle-ultraviolet emission at 310 nm from the Zn2SiO4 phase.

  19. High-Order Weno Simulations of Three-Dimensional Reshocked Richtmyer-Meshkov Instability to Late Times: Dynamics, Dependence on Initial Conditions, and Comparisons to Experimental Data

    SciTech Connect

    Schilling, O; Latini, M

    2010-01-12

    The dynamics of the reshocked multi-mode Richtmyer-Meshkov instability is investigated using 513 x 257{sup 2} three-dimensional ninth-order weighted essentially nonoscillatory shock-capturing simulations. A two-mode initial perturbation with superposed random noise is used to model the Mach 1.5 air/SF{sub 6} Vetter-Sturtevant shock tube experiment. The mass fraction and enstrophy isosurfaces, and density cross-sections are utilized to show the detailed flow structure before, during, and after reshock. It is shown that the mixing layer growth agrees well with the experimentally measured growth rate before and after reshock. The post-reshock growth rate is also in good agreement with the prediction of the Mikaelian model. A parametric study of the sensitivity of the layer growth to the choice of amplitudes of the short and long wavelength initial interfacial perturbation is also presented. Finally, the amplification effects of reshock are quantified using the evolution of the turbulent kinetic energy and turbulent enstrophy spectra, as well as the evolution of the baroclinic enstrophy production, buoyancy production, and shear production terms in the enstrophy and turbulent kinetic transport equations.

  20. Time-dependent modeling of oscillatory instability of three-dimensional natural convection of air in a laterally heated cubic box

    NASA Astrophysics Data System (ADS)

    Gelfgat, Alexander Yu.

    2017-08-01

    Transition from steady to oscillatory buoyancy convection of air in a laterally heated cubic box is studied numerically by straight-forward time integration of Boussinesq equations using a series of gradually refined finite volume grids. Horizontal and spanwise cube boundaries are assumed to be either perfectly thermally conducting or perfectly thermally insulated, which results in four different sets of thermal boundary conditions. Critical Grashof numbers are obtained by interpolation of numerically extracted growth/decay rates of oscillation amplitude to zero. Slightly supercritical flow regimes are described by time-averaged flows, snapshots, and spatial distribution of the oscillation amplitude. Possible similarities and dissimilarities with two-dimensional instabilities in laterally heated square cavities are discussed. Break of symmetries and sub- or supercritical character of bifurcations are examined. Three consequent transitions from steady to the oscillatory regime, from the oscillatory to the steady regime, and finally to the oscillatory flow, are found in the case of perfectly insulated horizontal and spanwise boundaries. Arguments for grid and time-step independence of the results are given.

  1. What drives gravitational instability in nearby star-forming spirals? The impact of CO and H i velocity dispersions

    NASA Astrophysics Data System (ADS)

    Romeo, Alessandro B.; Mogotsi, Keoikantse Moses

    2017-07-01

    The velocity dispersion of cold interstellar gas, σ, is one of the quantities that most radically affect the onset of gravitational instabilities in galaxy discs, and the quantity that is most drastically approximated in stability analyses. Here we analyse the stability of a large sample of nearby star-forming spirals treating molecular gas, atomic gas and stars as three distinct components, and using radial profiles of σCO and σ _{H I} derived from HERA CO-Line Extragalactic Survey (HERACLES) and The H i Nearby Galaxy Survey (THINGS) observations. We show that the radial variations of σCO and σ _{H I} have a weak effect on the local stability level of galaxy discs, which remains remarkably flat and well above unity, but is low enough to ensure (marginal) instability against non-axisymmetric perturbations and gas dissipation. More importantly, the radial variation of σCO has a strong impact on the size of the regions over which gravitational instabilities develop, and results in a characteristic instability scale that is one order of magnitude larger than the Toomre length of molecular gas. Disc instabilities are driven, in fact, by the self-gravity of stars at kiloparsec scales. This is true across the entire optical disc of every galaxy in the sample, with a few exceptions. In the linear phase of the disc-instability process, stars and molecular gas are strongly coupled, and it is such a coupling that ultimately triggers local gravitational collapse/fragmentation in the molecular gas.

  2. Dixdc1 is a critical regulator of DISC1 and embryonic cortical development

    PubMed Central

    Singh, Karun K.; Ge, Xuecai; Mao, Yingwei; Drane, Laurel; Meletis, Konstantinos; Samuels, Benjamin A.; Tsai, Li-Huei

    2010-01-01

    Summary The psychiatric illness risk gene Disrupted in Schizophrenia-1 (DISC1) plays an important role in brain development, however, it is unclear how DISC1 is regulated during cortical development. Here, we report that DISC1 is regulated during embryonic neural progenitor proliferation and neuronal migration through an interaction with DIX domain containing-1 (Dixdc1), the third mammalian gene discovered to contain a Disheveled-Axin (DIX) domain. We determined that Dixdc1 functionally interacts with DISC1 to regulate neural progenitor proliferation by co-modulating Wnt-GSK3β/β-catenin signaling. However, DISC1 and Dixdc1 do not regulate migration via this pathway. During neuronal migration, we discovered that phosphorylation of Dixdc1 by cyclin-dependent kinase 5 (Cdk5) facilitates its interaction with the DISC1-binding partner Ndel1. Furthermore, Dixdc1 phosphorylation and its interaction with DISC1/Ndel1 in vivo is required for neuronal migration. Together, these data reveal that Dixdc1 integrates DISC1 into Wnt-GSK3β/β-catenin-dependent and -independent signaling pathways during cortical development, and further delineate how DISC1 contributes to neuropsychiatric disorders. PMID:20624590

  3. Disc-protoplanet interaction. Influence of circumprimary radiative discs on self-gravitating protoplanetary bodies in binary star systems

    NASA Astrophysics Data System (ADS)

    Gyergyovits, M.; Eggl, S.; Pilat-Lohinger, E.; Theis, Ch.

    2014-06-01

    depend strongly on the state of the disc (i.e. quiet or dynamically evolving) - according to encounter-probability distributions, planet formation can be strongly altered if there is a dynamically evolving gas disc - and also on the smoothing parameter.

  4. Carbon, Nitrogen And α-Element Abundances Determine The Formation Sequence Of The Galactic Thick And Thin Discs

    NASA Astrophysics Data System (ADS)

    Gilmore, Gerry

    2016-09-01

    Using the DR12 public release of APOGEE data, we show that the thin and thick discs separate very well in the space defined by [α/Fe], [Fe/H] and [C/N]. Thick disc giants have both higher [C/N] and higher [α/Fe] than do thin disc stars with similar [Fe/H]. We deduce that the thick disc is composed of lower mass stars than the thin disc. Considering the fact that at a given metallicity there is a one-to-one relation between stellar mass and age, we are then able to infer the chronology of disc formation. Both the thick and the thin discs - defined by [α/Fe] - converge in their dependence on [C/N] and [C+N/Fe] at [Fe/H]≍-0.7. We conclude that (1) the majority of thick disc stars formed earlier than did the thin disc stars, (2) the formation histories of the thin and thick discs diverged early on, even when the [Fe/H] abundances are similar and (3) that the star formation rate in the thin disc has been lower than in the thick disc, at all metallicities.

  5. The effect of sustained compression on oxygen metabolic transport in the intervertebral disc decreases with degenerative changes.

    PubMed

    Malandrino, Andrea; Noailly, Jérôme; Lacroix, Damien

    2011-08-01

    Intervertebral disc metabolic transport is essential to the functional spine and provides the cells with the nutrients necessary to tissue maintenance. Disc degenerative changes alter the tissue mechanics, but interactions between mechanical loading and disc transport are still an open issue. A poromechanical finite element model of the human disc was coupled with oxygen and lactate transport models. Deformations and fluid flow were linked to transport predictions by including strain-dependent diffusion and advection. The two solute transport models were also coupled to account for cell metabolism. With this approach, the relevance of metabolic and mechano-transport couplings were assessed in the healthy disc under loading-recovery daily compression. Disc height, cell density and material degenerative changes were parametrically simulated to study their influence on the calculated solute concentrations. The effects of load frequency and amplitude were also studied in the healthy disc by considering short periods of cyclic compression. Results indicate that external loads influence the oxygen and lactate regional distributions within the disc when large volume changes modify diffusion distances and diffusivities, especially when healthy disc properties are simulated. Advection was negligible under both sustained and cyclic compression. Simulating degeneration, mechanical changes inhibited the mechanical effect on transport while disc height, fluid content, nucleus pressure and overall cell density reductions affected significantly transport predictions. For the healthy disc, nutrient concentration patterns depended mostly on the time of sustained compression and recovery. The relevant effect of cell density on the metabolic transport indicates the disturbance of cell number as a possible onset for disc degeneration via alteration of the metabolic balance. Results also suggest that healthy disc properties have a positive effect of loading on metabolic transport. Such

  6. Curveballs in protoplanetary discs - the effect of the Magnus force on planet formation

    NASA Astrophysics Data System (ADS)

    Forbes, John C.

    2015-10-01

    Spinning planetesimals in a gaseous protoplanetary disc may experience a hydrodynamical force perpendicular to their relative velocities. We examine the effect this force has on the dynamics of these objects using analytical arguments based on a simple laminar disc model and numerical integrations of the equations of motion for individual grains. We focus in particular on metre-sized boulders traditionally expected to spiral in to the central star in as little as 100 years from 1 au We find that there are plausible scenarios in which this force extends the lifetime of these solids in the disc by a factor of several. More importantly the velocities induced by the Magnus force can prevent the formation of planetesimals via gravitational instability in the inner disc if the size of the dust particles is larger than of the order of 10 cm. We find that the fastest growing linear modes of the streaming instability may still grow despite the diffusive effect of the Magnus force, but it remains to be seen how the Magnus force will alter the non-linear evolution of these instabilities.

  7. Zonal flow evolution and overstability in accretion discs

    NASA Astrophysics Data System (ADS)

    Vanon, R.; Ogilvie, G. I.

    2017-04-01

    This work presents a linear analytical calculation on the stability and evolution of a compressible, viscous self-gravitating (SG) Keplerian disc with both horizontal thermal diffusion and a constant cooling time-scale when an axisymmetric structure is present and freely evolving. The calculation makes use of the shearing sheet model and is carried out for a range of cooling times. Although the solutions to the inviscid problem with no cooling or diffusion are well known, it is non-trivial to predict the effect caused by the introduction of cooling and of small diffusivities; this work focuses on perturbations of intermediate wavelengths, therefore representing an extension to the classical stability analysis on thermal and viscous instabilities. For density wave modes, the analysis can be simplified by means of a regular perturbation analysis; considering both shear and thermal diffusivities, the system is found to be overstable for intermediate and long wavelengths for values of the Toomre parameter Q ≲ 2; a non-SG instability is also detected for wavelengths ≳18H, where H is the disc scale-height, as long as γ ≲ 1.305. The regular perturbation analysis does not, however, hold for the entropy and potential vorticity slow modes as their ideal growth rates are degenerate. To understand their evolution, equations for the axisymmetric structure's amplitudes in these two quantities are analytically derived and their instability regions obtained. The instability appears boosted by increasing the value of the adiabatic index and of the Prandtl number, while it is quenched by efficient cooling.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  9. Instability of rectangular jets

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Thies, Andrew T.

    1992-01-01

    The instability of rectangular jets is investigated using a vortex sheet model. It is shown that such jets support four linearly independent families of instability waves. Within each family there are infinitely many modes. A way to classify these modes according to the characteristics of their mode shapes or eigenfunctions is proposed. A parametric study of the instability wave characteristics has been carried out. A sample of the numerical results is reported here. It is found that the first and third modes of each instability wave family are corner modes. The pressure fluctuations associated with these instability waves are localized near the corners of the jet. The second mode, however, is a center mode with maximum fluctuations concentrated in the central portion of the jet flow. The center mode has the largest spatial growth rate. It is anticipated that as the instability waves propagate downstream the center mode would emerge as the dominant instability of the jet.

  10. Instability of rectangular jets

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Thies, Andrew T.

    1992-01-01

    The instability of rectangular jets is investigated using a vortex sheet model. It is shown that such jets support four linearly independent families of instability waves. Within each family there are infinitely many modes. A way to classify these modes according to the characteristics of their mode shapes or eigenfunctions is proposed. A parametric study of the instability wave characteristics has been carried out. A sample of the numerical results is reported here. It is found that the first and third modes of each instability wave family are corner modes. The pressure fluctuations associated with these instability waves are localized near the corners of the jet. The second mode, however, is a center mode with maximum fluctuations concentrated in the central portion of the jet flow. The center mode has the largest spatial growth rate. It is anticipated that as the instability waves propagate downstream the center mode would emerge as the dominant instability of the jet.

  11. Evolution of inclined planets in three-dimensional radiative discs

    NASA Astrophysics Data System (ADS)

    Bitsch, B.; Kley, W.

    2011-06-01

    Context. While planets in the solar system only have a low inclination with respect to the ecliptic there is mounting evidence that in extrasolar systems the inclination can be very high, at least for close-in planets. One process to alter the inclination of a planet is through planet-disc interactions. Recent simulations considering radiative transport have shown that the evolution of migration and eccentricity can strongly depend on the thermodynamic state of the disc. So far, this process has only been studied for a few selected planet masses using isothermal discs. Aims: We extend previous studies to investigate the planet-disc interactions of fixed and moving planets on inclined and eccentric orbits. We also analyse the effect of the disc's thermodynamic properties on the orbital evolution of embedded planets in detail. Methods: The protoplanetary disc is modelled as a viscous gas where the internally produced dissipation is transported by radiation. To solve the equations we use an explicit three-dimensional (3D) hydrodynamical code NIRVANA that includes full tensor viscosity, as well as implicit radiation transport in the flux-limited diffusion approximation. To speed up the simulations we apply the FARGO-algorithm in a 3D context. Results: For locally isothermal discs, we confirm previous results and find inclination damping and inward migration for planetary cores. For low inclinations (i ≲ 2H/r), the damping is exponential, while it follows di/dt ∝ i-2 for larger i. For radiative discs, the planetary migration is very limited, as long as their inclination exceeds a certain threshold. If the inclination is damped below this threshold, planetary cores with a mass up to ≈33 MEarth start to migrate outwards, while larger cores migrate inwards right from the start. The inclination is damped for all analysed planet masses. Conclusions: In a viscous disc an initial inclination of embedded planets will be damped for all planet masses. This damping occurs on

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

    NASA Astrophysics Data System (ADS)

    Ferreira, Jonathan; Petrucci, Pierre-Olivier; Garnier, Quentin

    2013-12-01

    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 different jet morphologies in the two cases.

  13. Nonlinear Dynamics of Single Bunch Instability

    SciTech Connect

    Stupakov, G.V.; Breizman, B.N.; Pekker, M.S.; /Texas U.

    2011-09-09

    A nonlinear equation is derived that governs the evolution of the amplitude of unstable oscillations with account of quantum diffusion effects due to the synchrotron radiation. Numerical solutions to this equation predict a variety of possible scenarios of nonlinear evolution of the instability some of which are in good qualitative agreement with experimental observations. Microwave single bunch instability in circular accelerators has been observed in many machines. The instability usually arises when the number of particles in the bunch exceeds some critical value, Nc, which varies depending on the parameters of the accelerating regime. Recent observations on the SLC damping rings at SLAC with a new low-impedance vacuum chamber revealed new interesting features of the instability. In some cases, after initial exponential growth, the instability eventually saturated at a level that remained constant through the accumulation cycle. In other regimes, relaxation-type oscillations were measured in nonlinear phase of the instability. In many cases, the instability was characterized by a frequency close to the second harmonic of the synchrotron oscillations. Several attempts have been made to address the nonlinear stage of the instability based on either computer simulations or some specific assumptions regarding the structure of the unstable mode. An attempt of a more general consideration of the problem is carried out in this paper. We adopt an approach recently developed in plasma physics for analysis of nonlinear behavior of weakly unstable modes in dynamic systems. Assuming that the growth rate of the instability is much smaller than its frequency, we find a time dependent solution to Vlasov equation and derive an equation for the complex amplitude of the oscillations valid in the nonlinear regime. Numerical solutions to this equation predict a variety of possible scenarios of nonlinear evolution of the instability some of which are in good qualitative agreement

  14. Hydrogel discs for digital microfluidics

    PubMed Central

    Fiddes, Lindsey K.; Luk, Vivienne N.; Au, Sam H.; Ng, Alphonsus H. C.; Luk, Victoria; Kumacheva, Eugenia; Wheeler, Aaron R.

    2012-01-01

    Hydrogels are networks of hydrophilic polymer chains that are swollen with water, and they are useful for a wide range of applications because they provide stable niches for immobilizing proteins and cells. We report here the marriage of hydrogels with digital microfluidic devices. Until recently, digital microfluidics, a fluid handling technique in which discrete droplets are manipulated electromechanically on the surface of an array of electrodes, has been used only for homogeneous systems involving liquid reagents. Here, we demonstrate for the first time that the cylindrical hydrogel discs can be incorporated into digital microfluidic systems and that these discs can be systematically addressed by droplets of reagents. Droplet movement is observed to be unimpeded by interaction with the gel discs, and gel discs remain stationary when droplets pass through them. Analyte transport into gel discs is observed to be identical to diffusion in cases in which droplets are incubated with gels passively, but transport is enhanced when droplets are continually actuated through the gels. The system is useful for generating integrated enzymatic microreactors and for three-dimensional cell culture. This paper demonstrates a new combination of techniques for lab-on-a-chip systems which we propose will be useful for a wide range of applications. PMID:22662096

  15. Analyses of the temporomandibular disc.

    PubMed

    Jirman, R; Fricová, M; Horák, Z; Krystůfek, J; Konvicková, S; Mazánek, J

    2007-01-01

    This project is the beginning of a large research work with a goal to develop a new total replacement of temporomandibular (TM) joint. First aim of this work was to determine the relative displacement of the TM disc and the mandible during mouth opening. The movement of the TM disc was studied using a magnetic resonance imaging. Sagittal static images in revolved sections of the TM joint were obtained in various positions of jaw opening from 0 to 50 mm. The results provided a description of the TM disc displacements as a function of jaw opening. The displacements of the mandible and TM disc were about 16 mm and 10 mm respectively at mouth opening of 50 mm, maximum rotation of the mandible was 34s. The results of these measurements can be used for clinical diagnostics and also they were used as inputs for the follows finite element analysis (FEA). Second aim of this work was to create stress and strain analysis of TM joint using non-linear FEA. Complex of TM joint consists of mandibular disc, half skull and half mandible during normal jaw opening. The results illustrate the stress distributions in the TMJ during a normal jaw opening.

  16. Evolution over time of the Milky Way's disc shape

    NASA Astrophysics Data System (ADS)

    Amôres, E. B.; Robin, A. C.; Reylé, C.

    2017-06-01

    Context. Galactic structure studies can be used as a path to constrain the scenario of formation and evolution of our Galaxy. The dependence with the age of stellar population parameters would be linked with the history of star formation and dynamical evolution. Aims: We aim to investigate the structures of the outer Galaxy, such as the scale length, disc truncation, warp and flare of the thin disc and study their dependence with age by using 2MASS data and a population synthesis model (the so-called Besançon Galaxy Model). Methods: We have used a genetic algorithm to adjust the parameters on the observed colour-magnitude diagrams at longitudes 80° ≤ ℓ ≤ 280° for | b | ≤ 5.5°. We explored parameter degeneracies and uncertainties. Results: We identify a clear dependence of the thin disc scale length, warp and flare shapes with age. The scale length is found to vary between 3.8 kpc for the youngest to about 2 kpc for the oldest. The warp shows a complex structure, clearly asymmetrical with a node angle changing with age from approximately 165° for old stars to 195° for young stars. The outer disc is also flaring with a scale height that varies by a factor of two between the solar neighbourhood and a Galactocentric distance of 12 kpc. Conclusions: We conclude that the thin disc scale length is in good agreement with the inside-out formation scenario and that the outer disc is not in dynamical equilibrium. The warp deformation with time may provide some clues to its origin.

  17. Numerical Modeling of Tidal Effects in Polytropic Accretion Discs

    NASA Technical Reports Server (NTRS)

    Godon, P.

    1996-01-01

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

  18. Conditions for circumstellar disc formation - II. Effects of initial cloud stability and mass accretion rate

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  19. Ranges of Cervical Intervertebral Disc Deformation during an In-Vivo Dynamic Flexion-Extension of the Neck.

    PubMed

    Yu, Yan; Mao, Haiqing; Li, Jing-Sheng; Tsai, Tsung-Yuan; Cheng, Liming; Wood, Kirkham B; Li, Guoan; Cha, Thomas D

    2017-03-23

    While abnormal loading is widely believed to cause cervical spine disc diseases, in-vivo cervical disc deformation during dynamic neck motion has not been well delineated. This study investigated the range of cervical disc deformation during an in-vivo functional flexion-extension of the neck. Ten asymptomatic human subjects were tested using a combined dual fluoroscopic imaging system and MRI based 3D modeling technique. Overall disc deformation was determined using the changes of the space geometry between upper and lower endplates of each intervertebral segment (C3/4, C4/5, C5/6 and C6/7). Five points (anterior, center, posterior, left and right) of each disc were analyzed to examine the disc deformation distributions. The data indicated that between the functional maximum flexion and extension of the neck, the anterior points of the discs experienced large changes of distraction/compression deformation and shear deformation. The higher level discs experienced higher ranges of disc deformation. No significant difference was found in deformation ranges at posterior points of all discs. The data indicated that the range of disc deformation is disc level dependent and the anterior region experienced larger changes of deformation than the center and posterior regions, except for the C6/7 disc. The data obtained from this study could serve as baseline knowledge for the understanding of the cervical spine disc biomechanics and for investigation of the biomechanical etiology of disc diseases. These data could also provide insights for development of motion preservation surgeries for cervical spine.

  20. Atomic gas in debris discs

    NASA Astrophysics Data System (ADS)

    Hales, Antonio S.; Barlow, M. J.; Crawford, I. A.; Casassus, S.

    2017-04-01

    We have conducted a search for optical circumstellar absorption lines in the spectra of 16 debris disc host stars. None of the stars in our sample showed signs of emission line activity in either Hα, Ca II or Na I, confirming their more evolved nature. Four stars were found to exhibit narrow absorption features near the cores of the photospheric Ca II and Na I D lines (when Na I D data were available). We analyse the characteristics of these spectral features to determine whether they are of circumstellar or interstellar origins. The strongest evidence for circumstellar gas is seen in the spectrum of HD 110058, which is known to host a debris disc observed close to edge-on. This is consistent with a recent ALMA detection of molecular gas in this debris disc, which shows many similarities to the β Pictoris system.

  1. Formation of discs around super-massive black hole binaries

    NASA Astrophysics Data System (ADS)

    Goicovic, Felipe G.; Cuadra, Jorge; Sesana, Alberto

    2016-02-01

    We model numerically the evolution of 104 M ⊙ turbulent molecular clouds in near-radial infall onto 106 M ⊙, equal-mass supermassive black hole binaries, using a modified version of the SPH code gadget-3. We investigate the different gas structures formed depending on the relative inclination between the binary and the cloud orbits. Our first results indicate that an aligned orbit produces mini-discs around each black hole, almost aligned with the binary; a perpendicular orbit produces misaligned mini-discs; and a counter-aligned orbit produces a circumbinary, counter-rotating ring.

  2. Imaging of post-operative spine in intervertebral disc pathology.

    PubMed

    Splendiani, A; D'Orazio, F; Patriarca, L; Arrigoni, F; Caranci, F; Fonio, P; Brunese, L; Barile, A; Di Cesare, E; Masciocchi, C

    2017-03-01

    This work is an imaging review of spine after surgery with special regard to imaging modality in intervertebral disc pathology. Advances in imaging technology can be evaluated. Depending on the clinical question is asked to the radiologist, it is possible to evaluate post-operative patients with conventional radiology (X-ray), computed tomography and magnetic resonance. Main indications for each technique are analysed. Imaging is important in the diagnosis of many forms of spine pathology and plays a fundamental role in evaluating post-surgical effects of treatments, according to the imaging method which is used, both on spine and on its surrounding tissues (intervertebral discs, spinal cord, muscles and vessels).

  3. Size-dependent axial instability of microtubules surrounded by cytoplasm of a living cell based on nonlocal strain gradient elasticity theory.

    PubMed

    Sahmani, S; Aghdam, M M

    2017-06-07

    Microtubules including tubulin heterodimers arranging in a parallel shape of cylindrical hollow plays an important role in the mechanical stiffness of a living cell. In the present study, the nonlocal strain gradient theory of elasticity including simultaneously the both nonlocality and strain gradient size dependency is put to use within the framework of a refined orthotropic shell theory with hyperbolic distribution of shear deformation to analyze the size-dependent buckling and postbuckling characteristics of microtubules embedded in cytoplasm under axial compressive load. The non-classical governing differential equations are deduced via boundary layer theory of shell buckling incorporating the nonlinear prebuckling deformation and microtubule-cytoplasm interaction in the living cell environment. Finally, with the aid of a two-stepped perturbation solution methodology, the explicit analytical expressions for nonlocal strain gradient stability paths of axially loaded microtubules are achieved. It is illustrated that by taking the nonlocal size effect into consideration, the critical buckling load of microtubule and its maximum deflection associated with the minimum postbuckling load decreases, while the strain gradient size dependency causes to increase them. Copyright © 2017 Elsevier Ltd. All rights reserved.

  4. Migrational Instabilities in Particle Suspensions

    NASA Technical Reports Server (NTRS)

    Goddard, Joe D.

    1996-01-01

    This work deals with an instability arising from the shear-induced migration of particles in dense suspensions coupled with a dependence of viscosity on particle concentration. The analysis summarized here treats the inertialess (Re = O) linear stability of homogeneous simple shear flows for a Stokesian suspension model of the type proposed by Leighton and Acrivos (1987). Depending on the importance of shear-induced migration relative to concentration-driven diffusion, this model admits short-wave instability arising from wave-vector stretching by the base flow and evolving into particle-depleted shear bands. Moreover, this instability in the time-dependent problem corresponds to loss of ellipticity in the associated static problem (Re = O, Pe = O). While the isotropic version of the Leighton-Acrivos model is found to be stable with their experimentally determined parameters for simple shear, it is known that the stable model does not give a good quantitative description of particle clustering in the core of pipe flow (Nott and Brady 1994). This leads to the conjecture that an appropriate variant on the above model could explain such clustering as a two-phase bifurcation in the base flow.

  5. Free motion around black holes with discs or rings: between integrability and chaos - IV

    NASA Astrophysics Data System (ADS)

    Witzany, V.; Semerák, O.; Suková, P.

    2015-08-01

    The dynamical system studied in previous papers of this series, namely a bound time-like geodesic motion in the exact static and axially symmetric space-time of an (originally) Schwarzschild black hole surrounded by a thin disc or ring, is considered to test whether the often employed `pseudo-Newtonian' approach (resorting to Newtonian dynamics in gravitational potentials modified to mimic the black hole field) can reproduce phase-space properties observed in the relativistic treatment. By plotting Poincaré surfaces of section and using two recurrence methods for similar situations as in the relativistic case, we find similar tendencies in the evolution of the phase portrait with parameters (mainly with mass of the disc/ring and with energy of the orbiters), namely those characteristic to weakly non-integrable systems. More specifically, this is true for the Paczyński-Wiita and a newly suggested logarithmic potential, whereas the Nowak-Wagoner potential leads to a different picture. The potentials and the exact relativistic system clearly differ in delimitation of the phase-space domain accessible to a given set of particles, though this mainly affects the chaotic sea whereas not so much the occurrence and succession of discrete dynamical features (resonances). In the pseudo-Newtonian systems, the particular dynamical features generally occur for slightly smaller values of the perturbation parameters than in the relativistic system, so one may say that the pseudo-Newtonian systems are slightly more prone to instability. We also add remarks on numerics (a different code is used than in previous papers), on the resemblance of dependence of the dynamics on perturbing mass and on orbital energy, on the difference between the Newtonian and relativistic Bach-Weyl rings, and on the relation between Poincaré sections and orbital shapes within the meridional plane.

  6. Quantification of stochastic fragmentation of self-gravitating discs

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Using 2D smoothed particle hydrodynamics, we investigate the distribution of wait times between strong shocks in a turbulent, self-gravitating accretion disc. We show that the resulting distributions do not depend strongly on the cooling time or resolution of the disc and that they are consistent with the predictions of earlier work. We use the distribution of wait times between shocks to estimate the likelihood of stochastic fragmentation by gradual contraction of shear-resistant clumps on the cooling time-scale. We conclude that the stochastic fragmentation mechanism cannot change the radius at which fragmentation is possible by more than ˜20 per cent, restricting direct gravitational collapse as a mechanism for giant planet formation to the outer regions of protoplanetary discs.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    We report the analysis of 22 B-band light curves of the dwarf nova V4140 Sgr obtained with SOAR Optical Imager (SOI)/SOAR during two nights along the decline of a superoutburst in 2006 September 12-24 and in quiescence over 50 d following the superoutburst. 3D eclipse mapping of the outburst light curves indicates that the accretion disc is elliptical (eccentricity e = 0.13) and that superhump maximum occurs when the mass donor star is aligned with the bulge of the elliptical disc. The accretion disc is geometrically thin both in outburst and in quiescence; it fills the primary Roche lobe in the outburst and shrinks to about half this size in quiescence. The stability of the eclipse shape, width and depth along quiescence and the derived disc surface brightness distribution indicate that the quiescent accretion disc is in a high-viscosity, steady-state. Flickering mapping of the quiescent data reveals that the low-frequency flickering arises from an azimuthally extended stream-disc impact region at disc rim and from the innermost disc region, whereas the high-frequency flickering originates in the accretion disc. Assuming the disc-related flickering to be caused by fluctuations in the energy dissipation rate induced by magnetohydrodynamic turbulence (Geertsema & Achterberg), we find that the quiescent disc viscosity parameter is large, α ≃ 0.2-0.4, at all radii. The high-viscosity quiescent disc and the inferred low disc temperatures in superoutburst are inconsistent with expectations of the disc-instability model, and lead to the conclusion that the outbursts of V4140 Sgr are powered by mass transfer bursts from its donor star.

  8. Joint Instability and Osteoarthritis

    PubMed Central

    Blalock, Darryl; Miller, Andrew; Tilley, Michael; Wang, Jinxi

    2015-01-01

    Joint instability creates a clinical and economic burden in the health care system. Injuries and disorders that directly damage the joint structure or lead to joint instability are highly associated with osteoarthritis (OA). Thus, understanding the physiology of joint stability and the mechanisms of joint instability-induced OA is of clinical significance. The first section of this review discusses the structure and function of major joint tissues, including periarticular muscles, which play a significant role in joint stability. Because the knee, ankle, and shoulder joints demonstrate a high incidence of ligament injury and joint instability, the second section summarizes the mechanisms of ligament injury-associated joint instability of these joints. The final section highlights the recent advances in the understanding of the mechanical and biological mechanisms of joint instability-induced OA. These advances may lead to new opportunities for clinical intervention in the prevention and early treatment of OA. PMID:25741184

  9. 21 CFR 866.1620 - Antimicrobial susceptibility test disc.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... of antimicrobic-impregnated paper discs used to measure by a disc-agar diffusion technique or a disc... antimicrobial agents. In the disc-agar diffusion technique, bacterial susceptibility is ascertained by directly...

  10. 21 CFR 866.1620 - Antimicrobial susceptibility test disc.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... of antimicrobic-impregnated paper discs used to measure by a disc-agar diffusion technique or a disc... antimicrobial agents. In the disc-agar diffusion technique, bacterial susceptibility is ascertained by directly...

  11. 21 CFR 866.1620 - Antimicrobial susceptibility test disc.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... of antimicrobic-impregnated paper discs used to measure by a disc-agar diffusion technique or a disc... antimicrobial agents. In the disc-agar diffusion technique, bacterial susceptibility is ascertained by directly...

  12. 21 CFR 866.1620 - Antimicrobial susceptibility test disc.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... of antimicrobic-impregnated paper discs used to measure by a disc-agar diffusion technique or a disc... antimicrobial agents. In the disc-agar diffusion technique, bacterial susceptibility is ascertained by directly...

  13. The effects of anterior vacuum disc on surgical outcomes of degenerative versus spondylolytic spondylolisthesis: at a minimum two-year follow-up.

    PubMed

    Lin, Tung-Yi; Liao, Jen-Chung; Tsai, Tsung-Ting; Lu, Meng-Ling; Niu, Chi-Chien; Chen, Wen-Jer; Chen, Lih-Hui

    2014-10-02

    The vacuum phenomenon within the intervertebral disc usually represents disc degeneration. There are no reports in the English literature that focus on the effect of an anterior vacuum disc on surgical outcome of same-segment spondylolisthesis. Patients with degenerative spondylolisthesis (DS) or isthmic spondylolisthesis (IS) who underwent a spinal surgery between January 2005 and December 2006 were reviewed. Patients who met certain criteria, including (1) only mono-segment spondylolisthesis, (2) gas air within the disc space of the spondylolisthesis segment on preoperative radiographs, (3) having received posterior decompression, posterior pedicle screw fixation, and posterolateral fusion, and (4) at least 12 months of follow-up radiographs available to define the posterolateral fusion rate, were enrolled into the study. Four radiographic parameters (disc height, translation, intradiscal angle, segmental angle) were assessed. Two-year postoperative radiographs were used to determine whether the posterolateral segment was fused or not. Clinical outcome and complications during the follow-up period were documented. Incidence of the disc vacuum phenomenon was significantly higher in the IS group than in the DS group (p < 0.001). The IS group had more listhesis and a narrower disc height on preoperative static radiographs; however, the DS group had a more prominent angle and listhesis change in preoperative dynamic variables. The posterolateral fusion rate was significantly higher in the IS group (p = 0.019). The preoperative Oswestry Disability Index (ODI) score, the final ODI, and the ODI difference were similar between groups. More excellent and good results were seen in the IS group. Besides, better final ODI and results were seen in the bilateral fusion group than in the nonfusion group. The disc vacuum phenomenon is not equal to anterior instability absolutely. Determination of stability or instability in a vacuum disc should be considered by a

  14. Soft-tissue damage and segmental instability in adult patients with cervical spinal cord injury without major bone injury.

    PubMed

    Maeda, Takeshi; Ueta, Takayoshi; Mori, Eiji; Yugue, Itaru; Kawano, Osamu; Takao, Tsuneaki; Sakai, Hiroaki; Okada, Seiji; Shiba, Keiichiro

    2012-12-01

    A retrospective imaging and clinical study. To evaluate the extraneural soft-tissue damage and its clinical relevance in patients with traumatic cervical spinal cord injury (SCI) without major bone injury. To date, various kinds of cervical discoligamentous injuries have been demonstrated on magnetic resonance images in patients with SCI without bony injury. However, it has not been clear whether these magnetic resonance imaging abnormalities are actually related to spinal segmental instability and the patients' neurological status. Eighty-eight adult patients with acute traumatic cervical SCI without major bone injury were examined by flexion-extension lateral radiographs and magnetic resonance images within 2 days after trauma. We excluded patients with flexion recoil injury; therefore, most of the patients included were considered to have sustained a hyperextension injury. Instability of the injured cervical segment was defined when there was more than 3.5-mm posterior translation and/or more than a 11° difference in the intervertebral angle between the site of interest and adjacent segments. The neurological status was evaluated according to the American Spinal Injury Association motor score. On magnetic resonance images, the damage to the anterior longitudinal ligament and intervertebral disc were apparent in 44 and 37 patients, respectively. Various degrees of prevertebral fluid collection (prevertebral hyperintensity) were demonstrated in 76 patients. These magnetic resonance imaging abnormalities were significantly associated with initial cervical segmental instability as judged by flexion-extension radiographs. Interestingly, the American Spinal Injury Association motor score had a significant association with either magnetic resonance imaging abnormalities or segmental instability but not with the cervical canal diameter. A considerable proportion of the patients with traumatic cervical SCI without major bone injury were shown to have various types of

  15. Radiative heat transport instability in a laser produced inhomogeneous plasma

    SciTech Connect

    Bychenkov, V. Yu.; Rozmus, W.

    2015-08-15

    A laser produced high-Z plasma in which an energy balance is achieved due to radiation emission and radiative heat transfer supports ion acoustic instability. A linear dispersion relation is derived, and instability is compared to the radiation cooling instability [R. G. Evans, Plasma Phys. Controlled Fusion 27, 751 (1985)]. Under conditions of indirect drive fusion experiments, the driving term for the instability is the radiative heat flux and, in particular, the density dependence of the radiative heat conductivity. A specific example of thermal Bremsstrahlung radiation source has been considered. This instability may lead to plasma jet formation and anisotropic x-ray generation, thus affecting inertial confinement fusion related experiments.

  16. Drift Kelvin-Helmholtz instabilities in space plasmas

    NASA Technical Reports Server (NTRS)

    Sharma, Avadhesh C.; Srivastava, Krishna M.

    1992-01-01

    Drift Kelvin-Helmholtz instabilities of a finite-beta plasma in equilibrium electric and magnetic fields which are perpendicular to each other are studied using two fluid equations. Three types of these instabilities are considered including the magnetosonic instability of a finite beta-homogeneous plasma, the electrostatic drift instability of an inhomogeneous low-beta plasma, and the magneto-acoustic instability of a high-beta inhomogeneous isothermal plasma. It is shown that the electric field has either stabilizing or destabilizing effect depending on conditions under consideration.

  17. Ordinary electromagnetic mode instability

    NASA Technical Reports Server (NTRS)

    Cheng, C. Z.

    1974-01-01

    The instability of the ordinary electromagnetic mode propagating perpendicular to an external magnetic field is studied for a single-species plasma with ring velocity distribution. The marginal instability boundaries for both the purely growing mode and the propagating growing modes are calculated from the instability criteria. The dispersion characteristics for various sets of plasma parameters are also given. The typical growth rates are of the order of the cyclotron frequency.

  18. Instability in Rotating Machinery

    NASA Technical Reports Server (NTRS)

    1985-01-01

    The proceedings contain 45 papers on a wide range of subjects including flow generated instabilities in fluid flow machines, cracked shaft detection, case histories of instability phenomena in compressors, turbines, and pumps, vibration control in turbomachinery (including antiswirl techniques), and the simulation and estimation of destabilizing forces in rotating machines. The symposium was held to serve as an update on the understanding and control of rotating machinery instability problems.

  19. Generalities on combustion instabilities

    NASA Astrophysics Data System (ADS)

    Kuentzmann, Paul

    The main manifestations of combustion instabilities are reviewed, and the specific characteristics of instabilities in solid-propellant rocket engines are analyzed, with the Minuteman III third-stage engine and the SRB engine of Titan 34 D considered as examples. The main approaches for predicting combustion instabilities are discussed, including the linear approach based on the acoustic balance, the nonlinear mode-coupling approach, and the nonlinear approach using numerical calculation. Projected directions for future research are also examined.

  20. Cervical Disc Deformation During Flexion–Extension in Asymptomatic Controls and Single-Level Arthrodesis Patients

    PubMed Central

    Anderst, William; Donaldson, William; Lee, Joon; Kang, James

    2016-01-01

    The aim of this study was to characterize cervical disc deformation in asymptomatic subjects and single-level arthrodesis patients during in vivo functional motion. A validated model-based tracking technique determined vertebral motion from biplane radiographs collected during dynamic flexion–extension. Level-dependent differences in disc compression–distraction and shear deformation were identified within the anterior and posterior annulus (PA) and the nucleus of 20 asymptomatic subjects and 15 arthrodesis patients using a mixed-model statistical analysis. In asymptomatic subjects, disc compression and shear deformation per degree of flexion–extension progressively decreased from C23 to C67. The anterior and PA experienced compression–distraction deformation of up to 20%, while the nucleus region was compressed between 0% (C67) and 12% (C23). Peak shear deformation ranged from 16% (at C67) to 33% (at C45). In the C5–C6 arthrodesis group, C45 discs were significantly less compressed than in the control group in all disc regions (all p ≤ 0.026). In the C6–C7 arthrodesis group, C56 discs were significantly less compressed than the control group in the nucleus (p = 0.023) and PA (p = 0.014), but not the anterior annulus (AA; p = 0.137). These results indicate in vivo disc deformation is level-dependent, and single-level anterior arthrodesis alters the compression–distraction deformation in the disc immediately superior to the arthrodesis. PMID:23861160

  1. Jeans instability in a quantum dusty magnetoplasma

    SciTech Connect

    Salimullah, M.; Jamil, M.; Shah, H. A.; Murtaza, G.

    2009-01-15

    Jeans instability in a homogeneous cold quantum dusty plasma in the presence of the ambient magnetic field and the quantum effect arising through the Bohm potential has been examined using the quantum magnetohydrodynamic model. It is found that the Jeans instability is significantly reduced by the presence of the dust-lower-hybrid wave and the ion quantum effect. The minimum wavenumber for Jeans stability depends clearly on ion quantum effect and the dust-lower-hybrid frequency also.

  2. Electromechanical instability in suspended carbon nanotubes.

    PubMed

    Jonsson, L Magnus; Gorelik, Leonid Y; Shekhter, Robert I; Jonson, Mats

    2005-06-01

    We have theoretically investigated electromechanical properties of freely suspended carbon nanotubes when a current is injected into the tubes using a scanning tunneling microscope. We show that a shuttle-like electromechanical instability can occur if the bias voltage exceeds a dissipation-dependent threshold value. An instability results in large amplitude vibrations of the carbon nanotube bending mode, which modify the current-voltage characteristics of the system.

  3. What powers the starburst activity of NGC 1068? Star-driven gravitational instabilities caught in the act

    NASA Astrophysics Data System (ADS)

    Romeo, Alessandro B.; Fathi, Kambiz

    2016-08-01

    We explore the role that gravitational instability plays in NGC 1068, a nearby Seyfert galaxy that exhibits unusually vigorous starburst activity. For this purpose, we use the Romeo-Falstad disc instability diagnostics and data from the BIMA Survey of Nearby Galaxies, the Sloan Digital Sky Survey and the Spectrographic Areal Unit for Research on Optical Nebulae. Our analysis illustrates that NGC 1068 is a gravitationally unstable `monster'. Its starburst disc is subject to unusually powerful instabilities. Several processes, including feedback from the active galactic nucleus and starburst activity, try to quench such instabilities from inside out by depressing the surface density of molecular gas across the central kpc, but they do not succeed. Gravitational instability `wins' because it is driven by the stars via their much higher surface density. In this process, stars and molecular gas are strongly coupled, and it is such a coupling that ultimately triggers local gravitational collapse/fragmentation in the molecular gas.

  4. 26 CFR 1.246-4 - Dividends from a DISC or former DISC.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 3 2010-04-01 2010-04-01 false Dividends from a DISC or former DISC. 1.246-4... TAX (CONTINUED) INCOME TAXES Special Deductions for Corporations § 1.246-4 Dividends from a DISC or former DISC. The deduction provided in section 243 (relating to dividends received by corporations) is...

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Rotational support of giant clumps in high-z disc galaxies

    NASA Astrophysics Data System (ADS)

    Ceverino, Daniel; Dekel, Avishai; Mandelker, Nir; Bournaud, Frederic; Burkert, Andreas; Genzel, Reinhard; Primack, Joel

    2012-03-01

    We address the internal support against total free-fall collapse of the giant clumps that form by violent gravitational instability in high-z disc galaxies. Guidance is provided by an analytic model, where the protoclumps are cut from a rotating disc and collapse to equilibrium while preserving angular momentum. This model predicts prograde clump rotation, which dominates the support if the clump has contracted to a surface density contrast ≳10. This is confirmed in hydro adaptive mesh refinement zoom-in simulations of galaxies in a cosmological context. In most high-z clumps, the centrifugal force dominates the support, ?, where Vrot is the rotation velocity and the circular velocity Vcirc measures the potential well. The clump spin indeed tends to be in the sense of the global disc angular momentum, but substantial tilts are frequent, reflecting the highly warped nature of the high-z discs. Most clumps are in Jeans equilibrium, with the rest of the support provided by turbulence, partly driven by the gravitational instability itself. The general agreement between model and simulations indicates that angular momentum loss or gain in most clumps is limited to a factor of 2. Simulations of isolated gas-rich discs that resolve the clump substructure reveal that the cosmological simulations may overestimate ? by ˜30 per cent, but the dominance of rotational support at high z is not a resolution artefact. In turn, isolated gas-poor disc simulations produce at z= 0 smaller gaseous non-rotating transient clouds, indicating that the difference in rotational support is associated with the fraction of cold baryons in the disc. In our current cosmological simulations, the clump rotation velocity is typically more than twice the disc dispersion, Vrot˜ 100 km s-1, but when beam smearing of ≥0.1 arcsec is imposed, the rotation signal is reduced to a small gradient of ≤30 km s-1 kpc-1 across the clump. The velocity dispersion in the simulated clumps is comparable to the

  7. Magnetically elevated accretion discs in active galactic nuclei: broad emission-line regions and associated star formation

    NASA Astrophysics Data System (ADS)

    Begelman, Mitchell C.; Silk, Joseph

    2017-01-01

    We propose that the accretion discs fueling active galactic nuclei (AGN) are supported vertically against gravity by a strong toroidal (φ-direction) magnetic field that develops naturally as the result of an accretion disc dynamo. The magnetic pressure elevates most of the gas carrying the accretion flow at R to large heights z ≳ 0.1R and low densities, while leaving a thin dense layer containing most of the mass - but contributing very little accretion - around the equator. We show that such a disc model leads naturally to the formation of a broad emission-line region through thermal instability. Extrapolating to larger radii, we demonstrate that local gravitational instability and associated star formation are strongly suppressed compared to standard disc models for AGN, although star formation in the equatorial zone is predicted for sufficiently high mass supply rates. This new class of accretion disc models thus appears capable of resolving two longstanding puzzles in the theory of AGN fueling: the formation of broad emission-line regions and the suppression of fragmentation thought to inhibit accretion at the required rates. We show that the disc of stars that formed in the Galactic Center a few million years ago could have resulted from an episode of magnetically elevated accretion at ≳ 0.1 of the Eddington limit.

  8. Photoevaporating transitional discs and molecular cloud cores

    NASA Astrophysics Data System (ADS)

    Li, Min; Sui, Ning

    2017-04-01

    We investigate the evolution of photoevaporating protoplanetary discs including mass influx from molecular cloud cores. We examine the influence of cloud core properties on the formation and evolution of transitional discs. We use one-dimensional thin disc assumption and calculate the evolution of the protoplanetary disc. The effects of X-ray photoevaporation are also included. Our calculations suggest that most discs should experience the transitional disc phase within 10 Myr. The formation time of a gap and its initial location are functions of the properties of the cloud cores. In some circumstances, discs can open two gaps by photoevaporation alone. The two gaps form when the gas in the disc can expand to large radius and if the mass at large radius is sufficiently small. The surface density profile of the disc determines whether the two gaps can form. Since the structure of a disc is determined by the properties of a molecular cloud core, the core properties determine the formation of two gaps in the disc. We further find that even when the photoevaporation rate is reduced to 10 per cent of the standard value, two gaps can still form in the disc. The only difference is that the formation time is delayed.

  9. Electromagnetic Levitation of a Disc

    ERIC Educational Resources Information Center

    Valle, R.; Neves, F.; de Andrade, R., Jr.; Stephan, R. M.

    2012-01-01

    This paper presents a teaching experiment that explores the levitation of a disc of ferromagnetic material in the presence of the magnetic field produced by a single electromagnet. In comparison to the classical experiment of the levitation of a sphere, the main advantage of the proposed laboratory bench is that the uniform magnetic field…

  10. Optical Disc Applications in Libraries.

    ERIC Educational Resources Information Center

    Andre, Pamela Q. J.

    1989-01-01

    Discusses a variety of library applications of optical disc storage technology, including CD-ROM, digital videodisc, and WORM. Research and development projects at the Library of Congress, National Library of Medicine, and National Agricultural Library are described, products offered by library networks are reviewed, and activities in academic and…

  11. Electromagnetic Levitation of a Disc

    ERIC Educational Resources Information Center

    Valle, R.; Neves, F.; de Andrade, R., Jr.; Stephan, R. M.

    2012-01-01

    This paper presents a teaching experiment that explores the levitation of a disc of ferromagnetic material in the presence of the magnetic field produced by a single electromagnet. In comparison to the classical experiment of the levitation of a sphere, the main advantage of the proposed laboratory bench is that the uniform magnetic field…

  12. Twin Disc Gear Tooth Simulator

    DTIC Science & Technology

    1994-05-01

    temperature testing, i.e., aluminum, titanium alloys, or magnesium with Krytox . * Use adequate forced-draft ventilation. * Prior to conducting any...ultrasonic cleaner charged with Stoddard solvent. 2. Prior to installation, wipe all disc surfaces with a lint-free cloth dampened with Stoddard solvent

  13. Intervertebral disc calcifications in children.

    PubMed

    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.

  14. The relationship between quantitative measures of disc height and disc signal intensity with Pfirrmann score of disc degeneration.

    PubMed

    Salamat, Sara; Hutchings, John; Kwong, Clemens; Magnussen, John; Hancock, Mark J

    2016-01-01

    To assess the relationship between quantitative measures of disc height and signal intensity with the Pfirrmann disc degeneration scoring system and to test the inter-rater reliability of the quantitative measures. Participants were 76 people who had recently recovered from their last episode of acute low back pain and underwent MRI scan on a single 3T machine. At all 380 lumbar discs, quantitative measures of disc height and signal intensity were made by 2 independent raters and compared to Pfirrmann scores from a single radiologist. For quantitative measures of disc height and signal intensity a "raw" score and 2 adjusted ratios were calculated and the relationship with Pfirrmann scores was assessed. The inter-tester reliability of quantitative measures was also investigated. There was a strong linear relationship between quantitative disc signal intensity and Pfirrmann scores for grades 1-4, but not for grades 4 and 5. For disc height only, Pfirrmann grade 5 had significantly reduced disc height compared to all other grades. Results were similar regardless of whether raw or adjusted scores were used. Inter-rater reliability for the quantitative measures was excellent (ICC > 0.97). Quantitative measures of disc signal intensity were strongly related to Pfirrmann scores from grade 1 to 4; however disc height only differentiated between grade 4 and 5 Pfirrmann scores. Using adjusted ratios for quantitative measures of disc height or signal intensity did not significantly alter the relationship with Pfirrmann scores.

  15. Mre11 deficiency in Arabidopsis is associated with chromosomal instability in somatic cells and Spo11-dependent genome fragmentation during meiosis.

    PubMed

    Puizina, Jasna; Siroky, Jiri; Mokros, Petr; Schweizer, Dieter; Riha, Karel

    2004-08-01

    The Mre11/Rad50/Nbs1 complex is involved in many aspects of chromosome metabolism. Aberrant function of the complex is associated with defects in the DNA checkpoint, double-strand break repair, meiosis, and telomere maintenance. In this article, we report the consequences of Mre11 dysfunction for the stability of mitotic and meiotic chromosomes in Arabidopsis thaliana. Although plants homozygous for a T-DNA insertion in a conserved region of the MRE11 gene are viable, they exhibit growth defects and are infertile. Analysis of mitotic chromosomes prepared from the mutant plants revealed abundant dicentric chromosomes and chromosomal fragments. Fluorescence in situ hybridization showed that anaphase bridges are often formed by homologous chromosome arms. The frequency of chromosome fusions was not reduced in mre11 ku70 double mutants, suggesting that plants possess DNA end-joining activities independent of the Ku70/80 and Mre11 complexes. Cytogenetic examination of pollen mother cells revealed massive chromosome fragmentation and the absence of synapsis in the initial stages of meiosis. The fragmentation was substantially suppressed in mre11 spo11-1 double mutants, indicating that Mre11 is required for repair but not for the induction of Spo11-dependent meiotic DNA breaks in Arabidopsis.

  16. Instability of colliding metastable strings

    NASA Astrophysics Data System (ADS)

    Hiramatsu, Takashi; Eto, Minoru; Kamada, Kohei; Kobayashi, Tatsuo; Ookouchi, Yutaka

    2014-01-01

    The breaking of U(1) R symmetry plays a crucial role in modeling the breaking of supersymmetry (SUSY). In the models that possess both SUSY preserving and SUSY breaking vacua, tube-like cosmic strings called R-tubes, whose surfaces are constituted by domain walls interpolating a false and a true vacuum with some winding numbers, can exist. Their (in)stability can strongly constrain SUSY breaking models theirselves. In the present study, we investigate the dynamical (in)stability of two colliding metastable tube-like strings by field-theoretic simulations. From them, we find that the strings become unstable, depending on the relative collision angle and speed of two strings, and the false vacuum is eventually filled out by the true vacuum owing to rapid expansion of the strings or unstable bubbles created as remnants of the collision.

  17. Research on aviation fuel instability

    NASA Technical Reports Server (NTRS)

    Baker, C. E.; Bittker, D. A.; Cohen, S. M.; Seng, G. T.

    1984-01-01

    Current aircraft turbine fuels do not present a significant problem with fuel thermal stability. However, turbine fuels with broadened properties or nonpetroleum derived fuels may have reduced thermal stability because of their higher content of olefins, heteroatoms, and trace metals. Moreover, advanced turbine engines will increase the thermal stress on fuels because of their higher pressure ratios and combustion temperature. In recognition of the importance of this problem, NASA Lewis is currently engaged in a broadly based research effort to better understand the underlying causes of fuel thermal degradation. The progress and status of our various activities in this area are discussed. Topics covered include: nature of fuel instability and its temperature dependence, methods of measuring the instability, chemical mechanisms involved in deposit formation, and instrumental methods for characterizing fuel deposits. Finally, some preliminary thoughts on design approaches for minimizing the effects of lowered thermal stability are briefly discussed.

  18. Hagedorn instability in dimensionally reduced large-N gauge theories as Gregory-Laflamme and Rayleigh-Plateau instabilities.

    PubMed

    Azuma, Takehiro; Morita, Takeshi; Takeuchi, Shingo

    2014-08-29

    It is expected that the Gregory-Laflamme (GL) instability in the black string in gravity is related to the Rayleigh-Plateau instability in fluid mechanics. Especially, the orders of the phase transitions associated with these instabilities depend on the number of the transverse space dimensions, and they are of first and second order below and above the critical dimension. Through the gauge-gravity correspondence, the GL instability is conjectured to be thermodynamically related to the Hagedorn instability in large-N gauge theories, and it leads to a prediction that the order of the confinement-deconfinement transition associated with the Hagedorn instability may depend on the transverse dimension. We test this conjecture in the D-dimensional bosonic D0-brane model using numerical simulation and the 1/D expansion, and confirm the expected D dependence.

  19. Expression of DISC1-Interactome Members Correlates with Cognitive Phenotypes Related to Schizophrenia

    PubMed Central

    Rampino, Antonio; Walker, Rosie May; Torrance, Helen Scott; Anderson, Susan Maguire; Fazio, Leonardo; Di Giorgio, Annabella; Taurisano, Paolo; Gelao, Barbara; Romano, Raffaella; Masellis, Rita; Ursini, Gianluca; Caforio, Grazia; Blasi, Giuseppe; Millar, J. Kirsty; Porteous, David John; Thomson, Pippa Ann; Bertolino, Alessandro; Evans, Kathryn Louise

    2014-01-01

    Cognitive dysfunction is central to the schizophrenia phenotype. Genetic and functional studies have implicated Disrupted-in-Schizophrenia 1 (DISC1), a leading candidate gene for schizophrenia and related psychiatric conditions, in cognitive function. Altered expression of DISC1 and DISC1-interactors has been identified in schizophrenia. Dysregulated expression of DISC1-interactome genes might, therefore, contribute to schizophrenia susceptibility via disruption of molecular systems required for normal cognitive function. Here, the blood RNA expression levels of DISC1 and DISC1-interacting proteins were measured in 63 control subjects. Cognitive function was assessed using neuropsychiatric tests and functional magnetic resonance imaging was used to assess the activity of prefrontal cortical regions during the N-back working memory task, which is abnormal in schizophrenia. Pairwise correlations between gene expression levels and the relationship between gene expression levels and cognitive function and N-back-elicited brain activity were assessed. Finally, the expression levels of DISC1, AKAP9, FEZ1, NDEL1 and PCM1 were compared between 63 controls and 69 schizophrenic subjects. We found that DISC1-interactome genes showed correlated expression in the blood of healthy individuals. The expression levels of several interactome members were correlated with cognitive performance and N-back-elicited activity in the prefrontal cortex. In addition, DISC1 and NDEL1 showed decreased expression in schizophrenic subjects compared to healthy controls. Our findings highlight the importance of the coordinated expression of DISC1-interactome genes for normal cognitive function and suggest that dysregulated DISC1 and NDEL1 expression might, in part, contribute to susceptibility for schizophrenia via disruption of prefrontal cortex-dependent cognitive functions. PMID:24940743

  20. Global evolution of the magnetic field in a thin disc and its consequences for protoplanetary systems

    NASA Astrophysics Data System (ADS)

    Guilet, Jérôme; Ogilvie, Gordon I.

    2014-06-01

    The strength and structure of the large-scale magnetic field in protoplanetary discs are still unknown, although they could have important consequences for the dynamics and evolution of the disc. Using a mean-field approach in which we model the effects of turbulence through enhanced diffusion coefficients, we study the time-evolution of the large-scale poloidal magnetic field in a global model of a thin accretion disc, with particular attention to protoplanetary discs. With the transport coefficients usually assumed, the magnetic field strength does not significantly increase radially inwards, leading to a relatively weak magnetic field in the inner part of the disc. We show that with more realistic transport coefficients that take into account the vertical structure of the disc and the back-reaction of the magnetic field on the flow as obtained by Guilet & Ogilvie, the magnetic field can significantly increase radially inwards. The magnetic field profile adjusts to reach an equilibrium value of the plasma β parameter (the ratio of mid-plane thermal pressure to magnetic pressure) in the inner part of the disc. This value of β depends strongly on the aspect ratio of the disc and on the turbulent magnetic Prandtl number, and lies in the range 104-107 for protoplanetary discs. Such a magnetic field is expected to affect significantly the dynamics of protoplanetary discs by increasing the strength of magnetohydrodynamic turbulence and launching an outflow. We discuss the implications of our results for the evolution of protoplanetary discs and for the formation of powerful jets as observed in T-Tauri star systems.

  1. Treatment of hip instability.

    PubMed

    Robbins, G M; Masri, B A; Garbuz, D S; Greidanus, N; Duncan, C P

    2001-10-01

    Instability after total hip arthroplasty is a major source of patient morbidity, second only to aseptic loosening. Certain patient groups have been identified as having a greater risk of instability, including patients undergoing revision arthroplasty as early or late treatment for proximal femoral fractures.

  2. Peripheral Disc Margin Shape and Internal Disc Derangement: Imaging Correlation in Significantly Painful Discs Identified at Provocation Lumbar Discography

    PubMed Central

    Bartynski, W.S.; Rothfus, W.E.

    2012-01-01

    Summary Annular margin shape is used to characterize lumbar disc abnormality on CT/MR imaging studies. Abnormal discs also have internal derangement including annular degeneration and radial defects. The purpose of this study was to evaluate potential correlation between disc-margin shape and annular internal derangement on post-discogram CT in significantly painful discs encountered at provocation lumbar discography (PLD). Significantly painful discs were encountered at 126 levels in 86 patients (47 male, 39 female) studied by PLD where no prior surgery had been performed and response to intradiscal lidocaine after provocation resulted in either substantial/total relief or no improvement after lidocaine administration. Post-discogram CT and discogram imaging was evaluated for disc-margin characteristics (bulge/protrusion), features of disc internal derangement (radial annular defect [RD: radial tear/fissure/annular gap], annular degeneration) and presence/absence of discographic contrast leakage. In discs with focal protrusion, 50 of 63 (79%) demonstrated Grade 3 RD with 13 (21%) demonstrating severe degenerative change only. In discs with generalized-bulge-only, 48 of 63 (76%) demonstrated degenerative change only (primarily Dallas Grade 3) with 15 of 63 (24%) demonstrating a RD (Dallas Grade 3). Differences were highly statistically significant (p<0.001). Pain elimination with intra-discal lidocaine correlated with discographic contrast leakage (p<0.001). Disc-margin shape correlates with features of internal derangement in significantly painful discs encountered at PLD. Discs with focal protrusion typically demonstrate RD while generalized bulging discs typically demonstrated degenerative changes only (p<0.001). Disc-margin shape may provide an important imaging clue to the cause of chronic discogenic low back pain. PMID:22681741

  3. Termination of the magnetorotational instability via parasitic instabilities in core-collapse supernovae

    NASA Astrophysics Data System (ADS)

    Rembiasz, T.; Obergaulinger, M.; Cerdá-Durán, P.; Müller, E.; Aloy, M. A.

    2016-03-01

    The magnetorotational instability (MRI) can be a powerful mechanism amplifying the magnetic field in core-collapse supernovae. Whether initially weak magnetic fields can be amplified by this instability to dynamically relevant strengths is still a matter of debate. One of the main uncertainties concerns the process that terminates the growth of the instability. Parasitic instabilities of both Kelvin-Helmholtz and tearing-mode type have been suggested to play a crucial role in this process, disrupting MRI channel flows and quenching magnetic field amplification. We perform two-dimensional and three-dimensional sheering-disc simulations of a differentially rotating protoneutron star layer in non-ideal magnetohydrodynamics with unprecedented high numerical accuracy, finding that Kelvin-Helmholtz parasitic modes dominate tearing modes in the regime of large hydrodynamic and magnetic Reynolds numbers, as encountered close to the surface of protoneutron stars. They also determine the maximum magnetic field stress achievable during the exponential growth of the MRI. Our results are consistent with the theory of parasitic instabilities based on a local stability analysis. To simulate the Kelvin-Helmholtz instabilities properly, a very high numerical resolution is necessary. Using ninth-order spatial reconstruction schemes, we find that at least eight grid zones per MRI channel are necessary to simulate the growth phase of the MRI and reach an accuracy of ˜10 per cent in the growth rate, while more than ˜60 zones per channel are required to achieve convergent results for the value of the magnetic stress at MRI termination.

  4. [Optic disc granuloma secondary to sarcoidosis].

    PubMed

    Qu-Knafo, L; Auregan-Giocanti, A

    2017-02-01

    We report a case of optic disc granuloma due to sarcoidosis. A 64-year-old, caucasian female with a history of pulmonary sarcoidosis presented with a vision loss on her left eye. The ophthalmologic examination revealed a discrete optic disc infiltrate compatible with the diagnosis of optic disc granuloma. Fluorescein angiography showed diffusion and impregnation of the granuloma without vascularitis. The optical coherence tomography demonstrated a homogenous and isoreflective lesion at the optic disc. The patient recovered her visual acuity after systemic corticosteroid treatment. Isolated optic disc granuloma is a rare condition of ocular sarcoidosis.

  5. Sealing arrangement with annular flexible disc

    DOEpatents

    Pennell, William E.; Honigsberg, Charles A.

    1983-01-01

    Fluid sealing arrangements including an annular shaped flexible disc having enlarged edges disposed within channel-shaped annular receptacles which are spaced from one another. The receptacles form an annular region for contacting and containing the enlarged edges of the disc, and the disc is preloaded to a conical configuration. The disc is flexibly and movably supported within the receptacles so that unevenly distributed relative motion between the components containing the receptacles is accommodated without loss of sealing contact between the edges of the disc and the walls of the receptacles.

  6. Carbon, nitrogen and α-element abundances determine the formation sequence of the Galactic thick and thin discs

    NASA Astrophysics Data System (ADS)

    Masseron, T.; Gilmore, G.

    2015-10-01

    Using the DR12 public release of APOGEE data, we show that the thin and thick discs separate very well in the space defined by [α/Fe], [Fe/H] and [C/N]. Thick disc giants have both higher [C/N] and higher [α/Fe] than do thin disc stars with similar [Fe/H]. We deduce that the thick disc is composed of lower mass stars than the thin disc. Considering the fact that at a given metallicity there is a one-to-one relation between stellar mass and age, we are then able to infer the chronology of disc formation. Both the thick and the thin discs - defined by [α/Fe] - converge in their dependence on [C/N] and [C+N/Fe] at [Fe/H]≈-0.7. We conclude that (1) the majority of thick disc stars formed earlier than did the thin disc stars, (2) the formation histories of the thin and thick discs diverged early on, even when the [Fe/H] abundances are similar and (3) that the star formation rate in the thin disc has been lower than in the thick disc, at all metallicities. Although these general conclusions remain robust, we also show that current stellar evolution models cannot reproduce the observed C/N ratios for thick disc stars. Unexpectedly, reduced or inhibited canonical extra mixing is very common in field stars. While subject to abundance calibration zero-point uncertainties, this implies a strong dependence of non-canonical extra mixing along the red giant branch on the initial composition of the star and in particular on the α-elemental abundance.

  7. The Transition between the Inner Disc and the Innermost Galactic Regions

    NASA Astrophysics Data System (ADS)

    Bono, G.; Genovali, K.; Lemasle, B.; Romaniello, M.; Nonino, M.; Bergemann, M.; Buonanno, R.; Fabrizio, M.; François, P.; Inno, L.; Laney, C.; Matsunaga, N.; Pedicelli, S.; Primas, F.; Thévenin, F.

    2015-05-01

    We discuss the iron and the α-element gradients in the Galactic disc and in the innermost Galactic regions (bulge, bar, nuclear bulge). Accurate spectroscopic measurements of young stellar tracers show a well defined iron gradient between the inner and the outer disc. The same outcome applies to light, α, and heavy elements. Moreover, the [α/Fe] ratio attains solar values over a significant fraction of the disc, in the bar and in the nuclear bulge. Thus suggesting that the slopes of iron and α-elements attain quite similar values. There is evidence of a mild enhancement in the outer disc, but this is the consequence of the steady decrease in iron abundance. Current findings do not allow us to constrain whether the chemical enrichment in the nuclear bulge and in the bar is currently driven by bar instabilities. The recent results by the ARGOS spectroscopic survey of intermediate-age stellar tracers (red clump) suggest that the metal-rich stellar components associated with the boxy/peanut bulge show evidence of a mild iron gradient, while the metal-poor component associated with the thick disc/halo shows a flat iron distribution across the bulge. The [α/Fe] ratio of the metal-rich components is slightly enhanced in the bulge, but attains a solar value in the disc. On the other hand, the metal-poor component is α-enhanced both in the bulge and at larger Galactocentric distances. The chemical enrichment history of the bulge supports N-body simulations suggesting that the bulge formed via a bar-forming and bar-buckling instabilities (Ness et al. 2013a,b).

  8. DISC1 is associated with cortical thickness and neural efficiency

    PubMed Central

    Brauns, Stefan; Gollub, Randy L.; Roffman, Joshua L.; Yendiki, Anastasia; Ho, Beng-Choon; Wassink, Thomas H.; Heinz, Andreas; Ehrlich, Stefan

    2011-01-01

    Background Disrupted in schizophrenia 1 (DISC1) is known to play a major role during brain development and is a candidate gene for schizophrenia. Cortical thickness is highly heritable and several MRI studies have shown widespread reductions of cortical thickness in patients with schizophrenia. Here, we investigated the effects of variation in DISC1 on cortical thickness. In a subsequent analysis we tested whether the identified DISC1 risk variant is also associated with neural activity during working memory functioning. Methods We acquired structural MRI (sMRI), functional MRI (fMRI) and genotype data from 96 healthy volunteers. Separate cortical statistical maps for five single nucleotide polymorphisms (SNP) of DISC1 were generated to detect differences of cortical thickness in genotype groups across the entire cortical surface. Working-memory related load-dependent activation was measured during the Sternberg Item Recognition Paradigm and analyzed using a region-of-interest approach. Results Phe allele carriers of the DISC1 SNP Leu607Phe had significantly reduced cortical thickness in the left supramarginal gyrus compared to Leu/Leu homozygotes. Neural activity in the left dorsolateral prefrontal cortex (DLPFC) during working memory task was increased in Phe allele carriers, whereas working memory performance did not differ between genotype groups. Conclusions This study provides convergent evidence for the effect of DISC1 risk variants on two independent brain-based intermediate phenotypes of schizophrenia. The same risk variant was associated with cortical thickness reductions and signs of neural inefficiency during a working memory task. Our findings provide further evidence for a neurodevelopmental model of schizophrenia. PMID:21642004

  9. On the chiral imbalance and Weibel instabilities

    NASA Astrophysics Data System (ADS)

    Kumar, Avdhesh; Bhatt, Jitesh R.; Kaw, P. K.

    2016-06-01

    We study the chiral-imbalance and the Weibel instabilities in presence of the quantum anomaly using the Berry-curvature modified kinetic equation. We argue that in many realistic situations, e.g. relativistic heavy-ion collisions, both the instabilities can occur simultaneously. The Weibel instability depends on the momentum anisotropy parameter ξ and the angle (θn) between the propagation vector and the anisotropy direction. It has maximum growth rate at θn = 0 while θn = π / 2 corresponds to a damping. On the other hand the pure chiral-imbalance instability occurs in an isotropic plasma and depends on difference between the chiral chemical potentials of right and left-handed particles. It is shown that when θn = 0, only for a very small values of the anisotropic parameter ξ ∼ξc, growth rates of the both instabilities are comparable. For the cases ξc < ξ ≪ 1 or ξ ≳ 1 at θn = 0, the Weibel modes dominate over the chiral-imbalance instability if μ5 / T ≤ 1. However, when μ5 / T ≥ 1, it is possible to have dominance of the chiral-imbalance modes at certain values of θn for an arbitrary ξ.

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

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Johansen, Anders

    2016-05-01

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

  11. Composition of early planetary atmospheres - II. Coupled Dust and chemical evolution in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Cridland, A. J.; Pudritz, Ralph E.; Birnstiel, Tilman; Cleeves, L. Ilsedore; Bergin, Edwin A.

    2017-08-01

    We present the next step in a series of papers devoted to connecting the composition of the atmospheres of forming planets with the chemistry of their natal evolving protoplanetary discs. The model presented here computes the coupled chemical and dust evolution of the disc and the formation of three planets per disc model. Our three canonical planet traps produce a Jupiter near 1 AU, a Hot Jupiter and a Super-Earth. We study the dependence of the final orbital radius, mass, and atmospheric chemistry of planets forming in disc models with initial disc masses that vary by 0.02 M⊙ above and below our fiducial model (M_{disc,0} = 0.1 M_{⊙}). We compute C/O and C/N for the atmospheres formed in our three models and find that C/Oplanet ˜ C/O_{disc}, which does not vary strongly between different planets formed in our model. The nitrogen content of atmospheres can vary in planets that grow in different disc models. These differences are related to the formation history of the planet, the time and location that the planet accretes its atmosphere, and are encoded in the bulk abundance of NH3. These results suggest that future observations of atmospheric NH3 and an estimation of the planetary C/O and C/N can inform the formation history of particular planetary systems.

  12. Secondary Instability in 3-D Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Wang, X.; Lin, Y.; Chen, L.

    2016-12-01

    3-D magnetic reconnection is investigated using the gyrokinetic-electron and fully-kinetic ion (GeFi) particle simulation model. The simulation is carried out in the force free current sheet for cases with a strong guide field BG as occurring in the solar and laboratory plasmas. It is found that, following the growth of the primary reconnection, a secondary instability is excited in the separatrix region, which leads to the electron heating and acceleration in the direction parallel to the magnetic field. The instability is due to the 3-D physics associated with a finite kz, where kz is the wave number along the guide field direction. Dependences of the growth rate of the secondary instability on the electron-ion resistivity, the ion-to-electron mass ratio mi/me, beta values, and the half-width of the current sheet are investigated. It is demonstrated that the secondary instability is of the magnetohydrodynamic (MHD) kink type.

  13. Parametric instability of two coupled nonlinear oscillators

    NASA Astrophysics Data System (ADS)

    Denardo, Bruce; Earwood, John; Sazonova, Vera

    1999-03-01

    One of the two normal modes of a system of two coupled nonlinear oscillators is subject to an instability. Several demonstration apparatus of weakly coupled oscillators that exhibit the instability are described. The effect is due to one normal mode parametrically driving the other, and occurs for the broad range of systems where the nonlinearity has a cubic contribution to the restoring force of each oscillator, which includes pendulums. The instability has an amplitude threshold that increases as the coupling is increased. A naive physical approach predicts that the mode opposite to that observed should be unstable. This is resolved by a weakly nonlinear analysis which reveals that the nonlinearity causes the linear frequency of a normal mode to depend upon the finite amplitude of the other mode. Numerical simulations confirm the theory, and extend the existence of the instability and the accuracy of the theoretical amplitude threshold beyond the regime of weak nonlinearity and weak coupling.

  14. Thermochemical modelling of brown dwarf discs

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

    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 discs are similar to scaled-down T Tauri discs is currently unknown, and this work is a step towards establishing a relationship through the eventual modelling of future observations. We use observations of the brown dwarf disc ρ Oph 102 to infer a fiducial model around which we build a small grid of brown dwarf disc models, in order to model the CO, HCN, and HCO+ line fluxes and the chemistry which drives their abundances. These are the first brown dwarf models to be published which relate detailed, 2D radiation thermochemical disc models to observational data. We predict that moderately extended ALMA antenna configurations will spatially resolve CO line emission around brown dwarf discs, and that HCN and HCO+ will be detectable in integrated flux, following our conclusion that the flux ratios of these molecules to CO emission are comparable to that of T Tauri discs. These molecules have not yet been observed in sub-mm wavelengths in a brown dwarf disc, yet they are crucial tracers of the warm surface-layer gas and of ionization in the outer parts of the disc. We present the prediction that if the physical and chemical processes in brown dwarf discs are similar to those that occur in T Tauri discs - as our models suggest - then the same diagnostics that are used for T Tauri discs can be used for brown dwarf discs (such as HCN and HCO+ lines that have not yet been observed in the sub-mm), and that these lines should be observable with ALMA. Through future observations, either confirmation (or refutation) of these ideas about brown dwarf disc chemistry will have strong implications for our understanding of disc chemistry, structure, and subsequent planet formation in brown

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  16. Highly inclined and eccentric massive planets. II. Planet-planet interactions during the disc phase

    NASA Astrophysics Data System (ADS)

    Sotiriadis, Sotiris; Libert, Anne-Sophie; Bitsch, Bertram; Crida, Aurélien

    2017-02-01

    produced by orbital instability and/or planet-planet scattering. When considering the long-term evolution over 100 Myr, destabilization of the resonant systems is common, and the percentage of highly mutually inclined systems still evolving in resonance drops to 30%. Finally, the parameters of the final system configurations are in very good agreement with the semi-major axis and eccentricity distributions in the observations, showing that planet-planet interactions during the disc phase could have played an important role in sculpting planetary systems.

  17. A self-consistent model for the evolution of the gas produced in the debris disc of β Pictoris

    NASA Astrophysics Data System (ADS)

    Kral, Q.; Wyatt, M.; Carswell, R. F.; Pringle, J. E.; Matrà, L.; Juhász, A.

    2016-09-01

    This paper presents a self-consistent model for the evolution of gas produced in the debris disc of β Pictoris. Our model proposes that atomic carbon and oxygen are created from the photodissociation of CO, which is itself released from volatile-rich bodies in the debris disc due to grain-grain collisions or photodesorption. While the CO lasts less than one orbit, the atomic gas evolves by viscous spreading resulting in an accretion disc inside the parent belt and a decretion disc outside. The temperature, ionization fraction and population levels of carbon and oxygen are followed with the photodissociation region model CLOUDY, which is coupled to a dynamical viscous α model. We present new gas observations of β Pic, of C I observed with Atacama Pathfinder EXperiment and O I observed with Herschel, and show that these along with published C II and CO observations can all be explained with this new model. Our model requires a viscosity α > 0.1, similar to that found in sufficiently ionized discs of other astronomical objects; we propose that the magnetorotational instability is at play in this highly ionized and dilute medium. This new model can be tested from its predictions for high-resolution ALMA observations of C I. We also constrain the water content of the planetesimals in β Pic. The scenario proposed here might be at play in all debris discs and this model could be used more generally on all discs with C, O or CO detections.

  18. Buckling instability in arteries.

    PubMed

    Vandiver, Rebecca M

    2015-04-21

    Arteries can become tortuous in response to abnormal growth stimuli, genetic defects and aging. It is suggested that a buckling instability is a mechanism that might lead to artery tortuosity. Here, the buckling instability in arteries is studied by examining asymmetric modes of bifurcation of two-layer cylindrical structures that are residually stressed. These structures are loaded by an axial force, internal pressure and have nonlinear, anisotropic, hyperelastic responses to stresses. Strain-softening and reduced opening angle are shown to lower the critical internal pressure leading to buckling. In addition, the ratio of the media thickness to the adventitia thickness is shown to have a dramatic impact on arterial instability.

  19. Accretion disc flows around FU Orionis stars

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    The accretion disk model of FU Orionis systems in outburst is investigated by examining the time-dependent behavior of a disk around a low-mass protostar that accretes at 0.00001-0.0001 solar masses/yr. It is found that the disk may be stabilized against the thermal ionization instability by the effect of advective heat transport and that it may therefore exist in the quasi-steady-state observed in post-outburst FU Orionis systems. The disk models are used to discuss the cosmochemical consequences of possible FU Ori events during the evolution of the primordial solar nebula.

  20. Effect of frozen storage on the creep behavior of human intervertebral discs.

    PubMed

    Dhillon, N; Bass, E C; Lotz, J C

    2001-04-15

    A biomechanical study of the compressive creep behavior of the human intervertebral disc before and after frozen storage. To determine whether frozen storage alters the time-dependent response of the intact human intervertebral disc. The biomechanical properties of the intervertebral disc are generally determined using specimens that have been previously frozen. Although it is well established that freezing does not alter the elastic response of the disc, recent data demonstrate that freezing permanently alters the time-dependent mechanical behavior of porcine discs. Twenty lumbar motion segments from 10 human spines were harvested between 12 and 36 hours postmortem. The specimens were randomly assigned to one of two groups: Group 1 was tested promptly, stored frozen for 3 weeks, then thawed, and tested a second time; Group 2 was stored frozen for 3 weeks, thawed, and then tested. Each specimen was subjected to 5 cycles of compressive creep under 1 MPa for 20 minutes, followed by a 40-minute recovery under no load. After testing each specimen was graded on a degeneration scale. A fluid transport model was used to parameterize the creep data. There was no statistically significant effect of freezing on the elastic or creep response of the discs. The degree of pre-existing degeneration had a significant effect on the creep response, with the more degenerated discs appearing more permeable. Frozen storage for a reasonable time with a typical method does not significantly alter the creep response of human lumbar discs. Freezing may produce subtle effects, but these potential artifacts do not appear to alter the discs' time-dependent behavior in any consequential way. These results may not apply to tissue kept frozen for long durations and with poor packaging.

  1. Nanodomain organization of rhodopsin in native human and murine rod outer segment disc membranes

    PubMed Central

    Whited, Allison M.; Park, Paul S.-H.

    2014-01-01

    Biological membranes display distinct domains that organize membrane proteins and signaling molecules to facilitate efficient and reliable signaling. The organization of rhodopsin, a G protein-coupled receptor, in native rod outer segment disc membranes was investigated by atomic force microscopy. Atomic force microscopy revealed that rhodopsin is arranged into domains of variable size, which we refer to herein as nanodomains, in native membranes. Quantitative analysis of 150 disc membranes revealed that the physical properties of nanodomains are conserved in humans and mice and that the properties of individual disc membranes can be variable. Examining the variable properties of disc membranes revealed some of the factors contributing to the size of rod outer segment discs and the formation of nanodomains in the membrane. The diameter of rod outer segment discs was dependent on the number of rhodopsin molecules incorporated into the membrane but independent of the spatial density of rhodopsin. The number of nanodomains present in a single disc was also dependent on the number of rhodopsin molecules incorporated into the membrane. The size of the nanodomains was largely independent of the number or spatial density of rhodopsin in the membrane. PMID:25305340

  2. Rayleigh-Taylor instability in an equal mass plasma

    SciTech Connect

    Adak, Ashish; Ghosh, Samiran; Chakrabarti, Nikhil

    2014-09-15

    The Rayleigh-Taylor (RT) instability in an inhomogeneous pair-ion plasma has been analyzed. Considering two fluid model for two species of ions (positive and negative), we obtain the possibility of the existence of RT instability. The growth rate of the RT instability as usual depends on gravity and density gradient scale length. The results are discussed in context of pair-ion plasma experiments.

  3. Quantification of intervertebral disc volume properties below spine fusion, using magnetic resonance imaging, in adolescent idiopathic scoliosis surgery.

    PubMed

    Violas, Philippe; Estivalezes, Erik; Briot, Jérome; Sales de Gauzy, Jérome; Swider, Pascal

    2007-07-01

    Prospective clinical study. A quantification of volume and hydration variation of the intervertebral discs, using magnetic resonance imaging (MRI), in the lumbar spine before and after surgery performed in adolescent idiopathic scoliosis (AIS). To evaluate an objective quantification of volume and hydration of intervertebral discs below spine fusion in scoliosis surgery. Repercussion of long spine fusion on the free lower lumbar spine is one of the major concerns of scoliosis surgery. However, the evolution of lumbar intervertebral disc below thoracolumbar fusions remains unknown. MRI performed in the clinical protocol, concerned 28 patients having an idiopathic scoliosis. They underwent posterior instrumentations. MRI was obtained before surgery, after surgery at 3 months and for 15 patients at 1 year. MRI data were posttreated using a custom-made image processing software to semiautomatically derive volume properties of disc, anulus fibrosus, and nucleus pulposus. The nucleus-disc volume ratio was also an indicator of the hydration level. The reliability of the three-dimensional reconstruction process was initially verified using an intraoperator reproducibility test. Original preoperative data on disc volume properties were then derived. Postoperative volume variations were quantified in discs below spine fusion taking into account the level of the arthrodesis and the disc location. It showed that the postoperative volume criteria increased significantly for nucleus, disc, and nucleus-disc volume ratio and some magnitude modulation could be conditioned by the location of surgical instrumentation. Some stabilization or reduction depending on disc level and arthrodesis size between 3 months and 1 year is observed in the follow-up. It tended to prove that the recovery of balance physiologic positioning and inherent biomechanical loads could induce a restored hydration of disc, which should favor the remodeling of free segments. This work was the first report

  4. Wet disc contraction to galactic blue nuggets and quenching to red nuggets

    NASA Astrophysics Data System (ADS)

    Dekel, A.; Burkert, A.

    2014-02-01

    We study the origin of high-redshift, compact, quenched spheroids (red nuggets) through the dissipative shrinkage of gaseous discs into compact star-forming systems (blue nuggets). The discs, fed by cold streams, undergo violent disc instability that drives gas into the centre (along with mergers). The inflow is dissipative when its time-scale is shorter than the star formation time-scale. This implies a threshold of ˜0.28 in the cold-to-total mass ratio within the disc radius. For the typical gas fraction ˜0.5 at z ˜ 2, this threshold is traced back to a maximum spin parameter of ˜0.05, implying that ˜half the star-forming galaxies contract to blue nuggets, while the rest form extended stellar discs. Thus, the surface density of blue galaxies is expected to be bimodal about ˜109 M⊙ kpc-2, slightly increasing with mass. The blue nuggets are expected to be rare at low z when the gas fraction is low. The blue nuggets quench to red nuggets by complementary internal and external mechanisms. Internal quenching by a compact bulge, in a fast mode and especially at high z, may involve starbursts, stellar and active galactic nucleus feedback, or Q-quenching. Quenching due to hot-medium haloes above 1012 M⊙ provides maintenance and a slower mode at low redshift. These predictions are confirmed in simulations and are consistent with observations at z = 0-3.

  5. Lumbar disc herniation: Is there an association between histological and magnetic resonance imaging findings?

    PubMed Central

    Majeed, Shiju A; Seshadrinath, N Arun Kumar; Binoy, Kavitha Ravi; Raji, Laila

    2016-01-01

    Background: Although validated radiological scoring systems and histological scoring system of surgically removed degenerated disc are used in assessment of progression of intervertebral disc degeneration, there have not been many studies that integrate these two aspects of assessments. The data available in this respect are very limited. This clinical study was designed to find the correlation between quantitative radiological score (Pfirmann grading system and Modic changes [MC]) and quantitative histological degeneration score (HDS). Materials and Methods: A cohort of 77 patients (45 males, 32 females; mean age of 38 years [range 18–58 years]) who presented with complaints of discogenic pain or radiculopathy at single level were assessed radiologically. They were graded according to the radiological pattern. The surgically excised disc specimen was graded according to HDS. The degree of radiological changes were correlated with the degree of histological changes. Results: Though the overall HDS (0–15) did not show statistically significant correlation with Pfirmann grading system, there were positive association found between mucoid degeneration, chondrocyte proliferation with the Pfirmann grading and mucoid degeneration, which were statistically significant. Female sex also had a higher association with instability pattern. Conclusion: The study shows that the Pfirmann grading system, MCs and HDS can reliably be used as scoring systems for assessing lumbar disc degeneration. The radiological assessment can be used as a noninvasive tool to assess the probable change in content rather than the microstructure of a disc undergoing degeneration. PMID:27293282

  6. Novel Human Intervertebral Disc Strain Template to Quantify Regional Three-Dimensional Strains in a Population and Compare to Internal Strains Predicted by a Finite Element Model

    PubMed Central

    Showalter, Brent L.; DeLucca, John F.; Peloquin, John M.; Cortes, Daniel H.; Yoder, Jonathon H.; Jacobs, Nathan T.; Wright, Alexander C.; Gee, James C.; Vresilovic, Edward J.; Elliott, Dawn M.

    2017-01-01

    Tissue strain is an important indicator of mechanical function, but is difficult to noninvasively measure in the intervertebral disc. The objective of this study was to generate a disc strain template, a 3D average of disc strain, of a group of human L4–L5 discs loaded in axial compression. To do so, magnetic resonance images of uncompressed discs were used to create an average disc shape. Next, the strain tensors were calculated pixel-wise by using a previously developed registration algorithm. Individual disc strain tensor components were then transformed to the template space and averaged to create the disc strain template. The strain template reduced individual variability while highlighting group trends. For example, higher axial and circumferential strains were present in the lateral and posterolateral regions of the disc, which may lead to annular tears. This quantification of group-level trends in local 3D strain is a significant step forward in the study of disc biomechanics. These trends were compared to a finite element model that had been previously validated against the disc-level mechanical response. Depending on the strain component, 81–99% of the regions within the finite element model had calculated strains within one standard deviation of the template strain results. The template creation technique provides a new measurement technique useful for a wide range of studies, including more complex loading conditions, the effect of disc pathologies and degeneration, damage mechanisms, and design and evaluation of treatments. PMID:26694516

  7. Chronic Ankle Instability

    MedlinePlus

    ... Risk for Newly Active Baby Boomers The American College of Foot and Ankle Surgeons has a valuable lesson for Baby Boomers now getting back into fitness and sports: Get your ankles checked for chronic instability caused ...

  8. Evaporatively driven morphological instability

    NASA Astrophysics Data System (ADS)

    Style, Robert W.; Wettlaufer, J. S.

    2007-07-01

    Simple observations of evaporating solutions reveal a complex hierarchy of spatiotemporal instabilities. We analyze one such instability suggested by the qualitative observations of Du and Stone and find that it is driven by a variant of the classical morphological instability in alloy solidification. In the latter case a moving solid-liquid interface is accompanied by a solutally enriched boundary layer that is thermodynamically metastable due to constitutional supercooling. Here, we consider the evaporation of an impure film adjacent to a solid composed of the nonvolatile species. In this case, constitutional supercooling within the film is created by evaporation at the solution-vapor interface and this drives the corrugation of the solid-solution interface across the thickness of the film. The principal points of this simple theoretical study are to suggest an instability mechanism that is likely operative across a broad range of technological and natural systems and to focus future quantitative experimental searches.

  9. Bacterial Genome Instability

    PubMed Central

    Darmon, Elise

    2014-01-01

    SUMMARY Bacterial genomes are remarkably stable from one generation to the next but are plastic on an evolutionary time scale, substantially shaped by horizontal gene transfer, genome rearrangement, and the activities of mobile DNA elements. This implies the existence of a delicate balance between the maintenance of genome stability and the tolerance of genome instability. In this review, we describe the specialized genetic elements and the endogenous processes that contribute to genome instability. We then discuss the consequences of genome instability at the physiological level, where cells have harnessed instability to mediate phase and antigenic variation, and at the evolutionary level, where horizontal gene transfer has played an important role. Indeed, this ability to share DNA sequences has played a major part in the evolution of life on Earth. The evolutionary plasticity of bacterial genomes, coupled with the vast numbers of bacteria on the planet, substantially limits our ability to control disease. PMID:24600039

  10. Evaluation of canine intervertebral disc degeneration in colour-coded computed tomography.

    PubMed

    Harder, Lisa K; Galindo-Zamora, Vladimir; Beyerbach, Martin; Nolte, Ingo; Wefstaedt, Patrick

    2015-01-01

    Canine intervertebral disc degeneration can lead to intervertebral disc disease. Mild degenerative changes in the structure of the canine intervertebral disc can be identified in magnetic resonance images, whereas these changes are not visible in computed tomographic images. Therefore, one aim of this study was to detect whether colour-coded computed tomography enhances the visibility of mild degenerative changes in the canine disc structure compared to non-contrast computed tomography. Furthermore, the study aimed to detect if intervertebral disc degeneration could be classified with a higher reliability in colour-coded images than in non-contrast images. Computed tomographic image studies of 144 canine intervertebral discs were coloured using three different lookup tables. Canine intervertebral disc degeneration was evaluated by three observers using a 5-grade classification system and compared to the evaluation of non-contrast CT and MRI images. A moderate to almost perfect intraobserver and a moderate to substantial interobserver agreement were found depending on the used colour code. On comparing non-contrast and colour-coded CT significant differences were found by one observer only. Significant differences in evaluation were found in grading intervertebral disc degeneration in MRI and colour-coded CT. Intervertebral disc degeneration could not be classified with a higher reliability on colour-coded images compared to non-contrast images. Furthermore, colour-coded CT did not enhance the visibility of mild degenerative changes in disc structure compared to non-contrast CT. However, the better intraobserver agreement and the subjective impression of the observers highlighted that the usage of colour encoded CT data sets with a wide range of tonal values of few primary and secondary colours may facilitate evaluation.

  11. Black hole mergers: can gas discs solve the `final parsec' problem?

    NASA Astrophysics Data System (ADS)

    Lodato, G.; Nayakshin, S.; King, A. R.; Pringle, J. E.

    2009-09-01

    We compute the effect of an orbiting gas disc in promoting the coalescence of a central supermassive black hole binary. Unlike earlier studies, we consider a finite mass of gas with explicit time dependence: we do not assume that the gas necessarily adopts a steady state or a spatially constant accretion rate, i.e. that the merging black hole was somehow inserted into a pre-existing accretion disc. We consider the tidal torque of the binary on the disc, and the binary's gravitational radiation. We study the effects of star formation in the gas disc in a simple energy feedback framework. The disc spectrum differs in detail from that found before. In particular, tidal torques from the secondary black hole heat the edges of the gap, creating bright rims around the secondary. These rims do not in practice have uniform brightness either in azimuth or time, but can on average account for as much as 50 per cent of the integrated light from the disc. This may lead to detectable high-photon-energy variability on the relatively long orbital time-scale of the secondary black hole, and thus offer a prospective signature of a coalescing black hole binary. We also find that the disc can drive the binary to merger on a reasonable time-scale only if its mass is at least comparable with that of the secondary black hole, and if the initial binary separation is relatively small, i.e. a0 <~ 0.05 pc. Star formation complicates the merger further by removing mass from the disc. In the feedback model we consider, this sets an effective limit to the disc mass. As a result, binary merging is unlikely unless the black hole mass ratio is <~0.001. Gas discs thus appear not to be an effective solution to the `last parsec' problem for a significant class of mergers.

  12. Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles

    PubMed Central

    Wu, Liang; Jackson, George; Müller, Erich A.

    2013-01-01

    We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids. PMID:23965962

  13. Dynamic Instability of Barlike Modes

    NASA Astrophysics Data System (ADS)

    Durisen, Richard H.; Pickett, Brian K.; Bate, Matthew R.; Imamura, James N.; Brandl, Andreas; Sterzik, Michael F.

    Numerical simulations during the 1980's established that prompt binary formation (or ``fission'') through dynamic growth of barlike modes is aborted by gravitational torques. Because these instabilities may occur during star formation and because their outcome over long times is still uncertain, we have combined various linear analyses with simulations by hydrodynamics codes to refine our understanding. We show that it is in fact the torques which cause nonlinear saturation of the mode amplitude. Excellent agreement for the early nonlinear phase is obtained using radically different hydrodynamics codes. However, the ultimate outcome is sensitive to assumptions about dissipative heating and is also somewhat code-dependent.

  14. Rotor internal friction instability

    NASA Technical Reports Server (NTRS)

    Bently, D. E.; Muszynska, A.

    1985-01-01

    Two aspects of internal friction affecting stability of rotating machines are discussed. The first role of internal friction consists of decreasing the level of effective damping during rotor subsynchronous and backward precessional vibrations caused by some other instability mechanisms. The second role of internal frication consists of creating rotor instability, i.e., causing self-excited subsynchronous vibrations. Experimental test results document both of these aspects.

  15. State Instability and Terrorism

    DTIC Science & Technology

    2010-01-01

    terrorism is a form ( Durkheim , 1930 [1951]; Useem, 1998). In addition, different types of instability ought to invite different levels of terrorism...society. The effects of the disruption in controls should be to increase levels of nonroutine collective action, of which terrorism is a form ( Durkheim ...instability at the country-level using a modified breakdown theoretical framework. This framework is based especially upon the work of Emile Durkheim

  16. Prediction of Algebraic Instabilities

    NASA Astrophysics Data System (ADS)

    Zaretzky, Paula; King, Kristina; Hill, Nicole; Keithley, Kimberlee; Barlow, Nathaniel; Weinstein, Steven; Cromer, Michael

    2016-11-01

    A widely unexplored type of hydrodynamic instability is examined - large-time algebraic growth. Such growth occurs on the threshold of (exponentially) neutral stability. A new methodology is provided for predicting the algebraic growth rate of an initial disturbance, when applied to the governing differential equation (or dispersion relation) describing wave propagation in dispersive media. Several types of algebraic instabilities are explored in the context of both linear and nonlinear waves.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  18. [Polish nomenclature of lumbar disc disease].

    PubMed

    Radło, Paweł; Smetkowski, Andrzej; Tesiorowski, Maciej

    2014-01-01

    Lumbar disc herniation is one of the most common damage of musculoskeletal system. The incidence of pain of lumbosacral spine is estimated approximately on 60-90% in general population, whereas the incidence of disc herniation in patients experiencing low back pain is about 91%. Despite the high incidence and uncomplicated pathogenesis of disc disease there is a problem with the nomenclature. In the vast majority of cases, the naming confusion stems from ignorance of the etiology of low back pain. Different terminologies: morphological, topographical, Radiological and Clinical are used interchangeably. In addition, diagnosis is presented in a variety of languages: Polish, English and Latin. Moreover, the medical and traditional language are used alternately. The authors found in Polish literature more, than 20 terms to describe lumbar disc herniation. All of these terms in the meaning of the authors are used to determine one pathology--mechanical damage to the intervertebral disc and moving the disc material beyond the anatomical area.

  19. Turing instabilities on Cartesian product networks

    PubMed Central

    Asllani, Malbor; Busiello, Daniel M.; Carletti, Timoteo; Fanelli, Duccio; Planchon, Gwendoline

    2015-01-01

    The problem of Turing instabilities for a reaction-diffusion system defined on a complex Cartesian product network is considered. To this end we operate in the linear regime and expand the time dependent perturbation on a basis formed by the tensor product of the eigenvectors of the discrete Laplacian operators, associated to each of the individual networks that build the Cartesian product. The dispersion relation which controls the onset of the instability depends on a set of discrete wavelengths, the eigenvalues of the aforementioned Laplacians. Patterns can develop on the Cartesian network, if they are supported on at least one of its constitutive sub-graphs. Multiplex networks are also obtained under specific prescriptions. In this case, the criteria for the instability reduce to compact explicit formulae. Numerical simulations carried out for the Mimura-Murray reaction kinetics confirm the adequacy of the proposed theory. PMID:26245138

  20. Studies of eRHIC coherent instabilities

    SciTech Connect

    Wang G.; Blaskiewicz, M.

    2012-05-20

    In the presence of an effective coherent electron cooling, the rms ion bunch length in eRHIC will be kept at 8.3 cm for 250 GeV protons, which is much shorter than the current RHIC 45 cm rms bunch length. Together with the increased bunch intensity and total bunch number, coherent instabilities could be a potential limitation for achieving desired machine performance. In this study, we use the tracking code TRANFT to find thresholds and growth rates for single bunch and coupled bunch instabilities with linear chromaticity and amplitude dependent tune shift taken into account. Based on the simulation results, requirements of machine parameters such as rf voltage, linear chromaticity, and tune dependence of betatron amplitude are specified to suppress these instabilities.

  1. Anterior instability in the throwing shoulder.

    PubMed

    Savoie, Felix H; O'Brien, Michael J

    2014-06-01

    The disabled throwing shoulder is a multifactorial problem. Laxity of the glenohumeral joint is necessary to achieve a satisfactory velocity. Normal wear and tear with throwing may convert this normal amount of excessive translation into instability. Instability in the throwing athlete manifests itself in 2 forms: traumatic anterior instability that happens to occur in a throwing athlete and excessive anterior subluxation because of overuse that occurs in conjunction with the disabled throwing shoulder. In most cases, it is difficult to determine by physical examination or imaging how much laxity is too much; therefore, the managing physician should always err on the side of caution. A trial of rest and rehabilitation should always be attempted before any consideration of surgery. The multifactorial issues in the disabled throwing athlete should be corrected during this phase of treatment, including assessment and treatment of hip abnormalities, restoration of satisfactory core strength, correction of scapular dyskinesis, and an evaluation and correction of any biomechanical abnormalities in the throwing mechanism. Surgical management of anterior instability in the throwing shoulder depends on the mechanism of injury. The traumatic anterior instability patient is managed by acute surgical repair without a shift, utilizing mattress sutures to prevent suture chondromalacia on the humeral head or glenoid. The anterior laxity management centers on the posterior superior labrum, although occasionally the anterior labrum or capsule may be involved as well. Overall, symptomatic anterior instability is less common in the throwing shoulder. Jobe and colleagues are credited with the first successful technique for the correction of anterior instability in the throwing athlete, the anterior capsulolabral reconstruction by a subscapularis split. The success of this technique paved the way for the adoption of the current arthroscopic techniques that are utilized to correct

  2. Factors that influence recurrent lumbar disc herniation.

    PubMed

    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 (P<0.001) and higher body mass index (P=0.042) might be risk factors for recurrence. Modic endplate changes were statistically significantly greater in the recurrent group than in the non-recurrent group (P=0.032). Our study suggests that patients who had recurrent lumbar disc 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.

  3. Disc repositioning: does it really work?

    PubMed

    Gonçalves, João Roberto; Cassano, Daniel Serra; Rezende, Luciano; Wolford, Larry M

    2015-02-01

    Although limited, there is evidence to support the assumption that temporomandibular joint (TMJ) articular disc repositioning indeed works; to date, there is no evidence that TMJ articular disc repositioning does not work. Despite the controversy among professionals in private practice and academia, TMJ articular disc repositioning is a procedure based on (still limited) evidence; the opposition is based solely on clinical preference and influenced by the ability to perform it or not. Copyright © 2015 Elsevier Inc. All rights reserved.

  4. Propagating Instabilities in Solids

    NASA Astrophysics Data System (ADS)

    Kyriakides, Stelios

    1998-03-01

    Instability is one of the factors which limit the extent to which solids can be loaded or deformed and plays a pivotal role in the design of many structures. Such instabilities often result in localized deformation which precipitates catastrophic failure. Some materials have the capacity to recover their stiffness following a certain amount of localized deformation. This local recovery in stiffness arrests further local deformation and spreading of the instability to neighboring material becomes preferred. Under displacement controlled loading the propagation of the transition fronts can be achieved in a steady-state manner at a constant stress level known as the propagation stress. The stresses in the transition fronts joining the highly deformed zone to the intact material overcome the instability nucleation stresses and, as a result, the propagation stress is usually much lower than the stress required to nucleate the instability. The classical example of this class of material instabilities is L/"uders bands which tend to affect mild steels and other metals. Recent work has demonstrated that propagating instabilities occur in several other materials. Experimental and analytical results from four examples will be used to illustrate this point: First the evolution of L=FCders bands in mild steel strips will be revisited. The second example involves the evolution of stress induced phase transformations (austenite to martensite phases and the reverse) in a shape memory alloy under displacement controlled stretching. The third example is the crushing behavior of cellular materials such as honeycombs and foams made from metals and polymers. The fourth example involves the axial broadening/propagation of kink bands in aligned fiber/matrix composites under compression. The microstructure and, as a result, the micromechanisms governing the onset, localization, local arrest and propagation of instabilities in each of the four materials are vastly different. Despite this

  5. Mechanical Characterization of the Human Lumbar Intervertebral Disc Subjected to Impact Loading Conditions

    NASA Astrophysics Data System (ADS)

    Jamison, David, IV

    Low back pain is a large and costly problem in the United States. Several working populations, such as miners, construction workers, forklift operators, and military personnel, have an increased risk and prevalence of low back pain compared to the general population. This is due to exposure to repeated, transient impact shocks, particularly while operating vehicles or other machinery. These shocks typically do not cause acute injury, but rather lead to pain and injury over time. The major focus in low back pain is often the intervertebral disc, due to its role as the major primary load-bearing component along the spinal column. The formation of a reliable standard for human lumbar disc exposure to repeated transient shock could potentially reduce injury risk for these working populations. The objective of this project, therefore, is to characterize the mechanical response of the lumbar intervertebral disc subjected to sub-traumatic impact loading conditions using both cadaveric and computational models, and to investigate the possible implications of this type of loading environment for low back pain. Axial, compressive impact loading events on Naval high speed boats were simulated in the laboratory and applied to human cadaveric specimen. Disc stiffness was higher and hysteresis was lower than quasi-static loading conditions. This indicates a shift in mechanical response when the disc is under impact loads and this behavior could be contributing to long-term back pain. Interstitial fluid loss and disc height changes were shown to affect disc impact mechanics in a creep study. Neutral zone increased, while energy dissipation and low-strain region stiffness decreased. This suggests that the disc has greater clinical instability during impact loading with progressive creep and fluid loss, indicating that time of day should be considered for working populations subjected to impact loads. A finite element model was developed and validated against cadaver specimen

  6. Multi stage three-dimensional sweeping and annealing of disc galaxies in clusters

    NASA Astrophysics Data System (ADS)

    Schulz, Steven; Struck, Curtis

    2001-11-01

    We present new three-dimensional, hydrodynamic simulations of the ram pressure stripping of disc galaxies via interaction with a hot intracluster medium (ICM). The simulations were carried with the smoothed-particle hydrodynamics, adaptive mesh `hydra' code (SPH-AP3M), with model galaxies consisting of gas and stellar disc components and dark haloes. The simulations also include radiative cooling, which is important for keeping the warm, diffuse gas of moderate density from being unrealistically heated by the ICM. We examine the role that wind velocity, density and galaxy tilt play in gas stripping. We include cases with lower ram pressures than other recent studies. In accord with previous studies, we find that low column density gas is promptly removed from the outer disc. However, we also find that not all of the gas stripped from the disc escapes immediately from the halo, some of material can linger for times of order 108yr. We use a simple analytic model to demonstrate that gas elements in the ICM wind feel an effective potential with a minimum displaced downstream from the halo centre. The onset of the ICM wind has a profound effect on the disc gas that is not immediately stripped. This remnant disc is displaced relative to the halo centre and compressed. This can trigger gravitational instability and the formation of numerous flocculent spirals. These waves transport angular momentum outward, resulting in further compression of the inner disc and the formation of a prominent gas ring. This `annealing' process makes the inner disc, which contains much of the total gas mass, resistant to further stripping, but presumably susceptible to global starbursts. Spirals in the outer disc stretch, shear and are eventually stripped on time-scales of a few times 108yr, after which time, mass and angular momentum loss effectly cease. For inclined galaxies, these effects are considerably modified over the same time-scale. The amount of mass loss is reduced. In addition

  7. On the dynamics of planetesimals embedded in turbulent protoplanetary discs with dead zones

    NASA Astrophysics Data System (ADS)

    Gressel, Oliver; Nelson, Richard P.; Turner, Neal J.

    2011-08-01

    Accretion in protoplanetary discs is thought to be driven by magnetohydrodynamic (MHD) turbulence via the magnetorotational instability. Recent work has shown that a planetesimal swarm embedded in a fully turbulent disc is subject to strong excitation of the velocity dispersion, leading to collisional destruction of bodies with radii Rp < 100 km. Significant diffusion of planetesimal semimajor axes also arises, leading to large-scale spreading of the planetesimal population throughout the inner regions of the protoplanetary disc, in apparent contradiction of constraints provided by the distribution of asteroids within the asteroid belt. In this paper, we examine the dynamics of planetesimals embedded in vertically stratified turbulent discs, with and without dead zones. Our main aims are to examine the turbulent excitation of the velocity dispersion, and the radial diffusion, of planetesimals in these discs. We employ 3D MHD simulations using the shearing box approximation, along with an equilibrium chemistry model that is used to calculate the ionization fraction of the disc gas as a function of time and position. Ionization is assumed to arise because of stellar X-rays, galactic cosmic rays and radioactive nuclei. In agreement with our previous study, we find that planetesimals in fully turbulent discs develop large random velocities that will lead to collisional destruction/erosion for bodies with sizes below 100 km, and undergo radial diffusion on a scale ˜2.5 au over a 5 Myr disc lifetime. But planetesimals in a dead zone experience a much reduced excitation of their random velocities, and equilibrium velocity dispersions lie between the disruption thresholds for weak and strong aggregates for sizes Rp≤ 100 km. We also find that radial diffusion occurs over a much reduced length-scale ˜0.25 au over the disc lifetime, this being consistent with Solar system constraints. We conclude that planetesimal growth via mutual collisions between smaller bodies cannot

  8. The quiescent phase of galactic disc growth

    NASA Astrophysics Data System (ADS)

    Aumer, Michael; Binney, James; Schönrich, Ralph

    2016-07-01

    We perform a series of controlled N-body simulations of growing disc galaxies within non-growing, live dark matter haloes of varying mass and concentration. Our initial conditions include either a low-mass disc or a compact bulge. New stellar particles are continuously added on near-circular orbits to the existing disc, so spiral structure is continuously excited. To study the effect of combined spiral and giant molecular cloud (GMC) heating on the discs, we introduce massive, short-lived particles that sample a GMC mass function. An isothermal gas component is introduced for a subset of the models. We perform a resolution study and vary parameters governing the GMC population, the histories of star formation and radial scale growth. Models with GMCs and standard values for the disc mass and halo density provide the right level of self-gravity to explain the age-velocity dispersion relation of the solar neighbourhood (Snhd). GMC heating generates remarkably exponential vertical profiles with scaleheights that are radially constant and agree with observations of galactic thin discs. GMCs are also capable of significantly delaying bar formation. The amount of spiral-induced radial migration agrees with what is required for the metallicity distribution of the Snhd. However, in our standard models, the outward-migrating populations are not hot enough vertically to create thick discs. Thick discs can form in models with high baryon fractions, but the corresponding bars are too long, the young stellar populations too hot and the discs flare considerably.

  9. Accretion Discs Show Their True Colours

    NASA Astrophysics Data System (ADS)

    2008-07-01

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

  10. Total Disc Replacement in Lumbar Degenerative Disc Diseases

    PubMed Central

    2015-01-01

    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. PMID:26713139

  11. Mitigating the hosing instability in relativistic laser-plasma interactions

    NASA Astrophysics Data System (ADS)

    Ceurvorst, L.; Ratan, N.; Levy, M. C.; Kasim, M. F.; Sadler, J.; Scott, R. H. H.; Trines, R. M. G. M.; Huang, T. W.; Skramic, M.; Vranic, M.; Silva, L. O.; Norreys, P. A.

    2016-05-01

    A new physical model of the hosing instability that includes relativistic laser pulses and moderate densities is presented and derives the density dependence of the hosing equation. This is tested against two-dimensional particle-in-cell simulations. These simulations further examine the feasibility of using multiple pulses to mitigate the hosing instability in a Nd:glass-type parameter space. An examination of the effects of planar versus cylindrical exponential density gradients on the hosing instability is also presented. The results show that strongly relativistic pulses and more planar geometries are capable of mitigating the hosing instability which is in line with the predictions of the physical model.

  12. Beam-Plasma Instabilities in a 2D Yukawa Lattice

    SciTech Connect

    Kyrkos, S.; Kalman, G. J.; Rosenberg, M.

    2009-06-05

    We consider a 2D Yukawa lattice of grains, with a beam of other charged grains moving in the lattice plane. In contrast to Vlasov plasmas, where the electrostatic instability excited by the beam is only longitudinal, here both longitudinal and transverse instabilities of the lattice phonons can develop. We determine and compare the transverse and longitudinal growth rates. The growth rate spectrum in wave number space exhibits remarkable gaps where no instability can develop. Depending on the system parameters, the transverse instability can be selectively excited.

  13. Multiphase Instabilities in Explosive Dispersal of Particles

    NASA Astrophysics Data System (ADS)

    Rollin, Bertrand; Ouellet, Frederick; Annamalai, Subramanian; Balachandar, S. ``Bala''

    2015-11-01

    Explosive dispersal of particles is a complex multiphase phenomenon that can be observed in volcanic eruptions or in engineering applications such as multiphase explosives. As the layer of particles moves outward at high speed, it undergoes complex interactions with the blast-wave structure following the reaction of the energetic material. Particularly in this work, we are interested in the multiphase flow instabilities related to Richmyer-Meshkov (RM) and Rayleigh-Taylor (RM) instabilities (in the gas phase and particulate phase), which take place as the particle layer disperses. These types of instabilities are known to depend on initial conditions for a relatively long time of their evolution. Using a Eulerian-Lagrangian approach, we study the growth of these instabilities and their dependence on initial conditions related to the particulate phase - namely, (i) particle size, (ii) initial distribution, and (iii) mass ratio (particles to explosive). Additional complexities associated with compaction of the layer of particles are avoided here by limiting the simulations to modest initial volume fraction of particles. A detailed analysis of the initial conditions and its effects on multiphase RM/RT-like instabilities in the context of an explosive dispersal of particles is presented. This work was supported by the U.S. Department of Energy, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement under the Predictive Science Academic Alliance Program, Contract No. DE-NA0002378.

  14. [Standardized terminology for disc disease].

    PubMed

    Sánchez Pérez, M; Gil Sierra, A; Sánchez Martín, A; Gallego Gómez, P; Pereira Boo, D

    2012-01-01

    This article reviews the terminology used to describe morphological alterations in the intervertebral discs. Radiologists must be able to communicate information about the type, location, and severity of these alterations to medical and surgical clinicians. It is crucial to use simple, standard, and unified terminology to ensure comprehension not only among radiologists but also with professionals from the different specialties for whom the radiology reports are written (fundamentally traumatologists and neurosurgeons). This terminology will help ensure a more accurate diagnosis and better patient management.

  15. Radiative transfer modelling of parsec-scale dusty warped discs

    NASA Astrophysics Data System (ADS)

    Jud, H.; Schartmann, M.; Mould, J.; Burtscher, L.; Tristram, K. R. W.

    2017-02-01

    Warped discs have been found on (sub-)parsec scale in some nearby Seyfert nuclei, identified by their maser emission. Using dust radiative transfer simulations, we explore their observational signatures in the infrared in order to find out whether they can partly replace the molecular torus. Strong variations of the brightness distributions are found, depending on the orientation of the warp with respect to the line of sight. Whereas images at short wavelengths typically show a disc-like and a point source component, the warp itself only becomes visible at far-infrared wavelengths. A similar variety is visible in the shapes of the spectral energy distributions. Especially for close to edge-on views, the models show silicate feature strengths ranging from deep absorption to strong emission for variations of the lines of sight towards the warp. To test the applicability of our model, we use the case of the Circinus galaxy, where infrared interferometry has revealed a highly elongated emission component matching a warped maser disc in orientation and size. Our model is for the first time able to present a physical explanation for the observed dust morphology as coming from the active galactic nuclei heated dust. As opposed to available torus models, a warped disc morphology produces a variety of silicate feature shapes for grazing lines of sight, close to an edge-on view. This could be an attractive alternative to a claimed change of the dust composition for the case of the nearby Seyfert 2 galaxy NGC 1068, which harbours a warped maser disc as well.

  16. Viscoelastic shear properties of porcine temporomandibular joint disc

    PubMed Central

    Wu, Yongren; Kuo, Jonathan; Wright, Gregory J.; Cisewski, Sarah E.; Wei, Feng; Kern, Michael J.; Yao, Hai

    2016-01-01

    Objectives To investigate the intrinsic viscoelastic shear properties in porcine TMJ discs. Materials and Methods Twelve fresh porcine TMJ discs from young adult pigs (6-8 months) were used. Cylindrical samples (5 mm diameter) with uniform thickness (~1.2 mm) were prepared from five regions of the TMJ disc. Torsional shear tests were performed under 10% compressive strain. Dynamic shear was applied in two methods: (1) a frequency sweep test over the frequency range of 0.01-10 rad/s with a constant shear strain amplitude of 0.025 rad, and (2) a strain sweep test over the range of 0.005-0.05 rad at a constant frequency of 10 rad/s. Transient stress-relaxation tests were also performed to determine the equilibrium shear properties. Results As the frequency increased in the frequency sweep test, the dynamic shear complex modulus increased, with values ranging from 7 to 17 kPa. The phase angle, ranging from 11 to 15 degrees, displayed no pattern of regional variation as the frequency increased. The dynamic shear modulus decreased as the shear strain increased. The equilibrium shear modulus had values ranging from 2 to 4.5 kPa. The posterior region had significantly higher values for dynamic shear modulus than those in the anterior region while no significant regional difference was found for equilibrium shear modulus. Conclusion Our results suggest that the intrinsic region-dependent viscoelastic shear characteristics of TMJ disc may play a crucial role in determining the local strain of the TMJ disc under mechanical loading. PMID:25865544

  17. An interpenetrating network composite for a regenerative spinal disc application.

    PubMed

    Chan, A H; Boughton, P C; Ruys, A J; Oyen, M L

    2017-01-01

    Severe degeneration of the intervertebral disc has an immensely debilitating effect on quality of life that has become a serious health and economic burden throughout the world. The disc plays an integral role in biomechanical movement and support within the spine. The emergence of tissue engineering endeavours to restore the structural characteristics and functionality of the native tissue. Hydrogels have been widely investigated as a candidate for regeneration of the gelatinous nucleus pulposus due to its architectural resemblance and fluid retention characteristics. However, hydrogels are often limited due to small compressive stiffness and tear resistance, leading to extrusion complications. Reinforcement of the hydrogel network using polymeric scaffolds may address these issues of inadequate mechanical properties and implant instability. This study investigates the potential of a carrageenan gel-infused polycaprolactone scaffold for nucleus pulposus tissue engineering. Mechanical properties were characterised using viscoelastic and poroelastic frameworks via microindentation. The incorporation of polymeric reinforcement within the gels increased material stiffness to that comparable to the native nucleus pulposus, however permeability was significantly greater than native values. A preliminary cell evaluation culturing NIH 3T3s over 21 days suggested the incorporation of polymeric networks also enhanced cellular proliferation compared to gels alone.

  18. A strongly truncated inner accretion disc in the Rapid Burster

    NASA Astrophysics Data System (ADS)

    van den Eijnden, J.; Bagnoli, T.; Degenaar, N.; Lohfink, A. M.; Parker, M. L.; in ‘t Zand, J. J. M.; Fabian, A. C.

    2017-03-01

    The neutron star (NS) low-mass X-ray binary (LMXB) the Rapid Burster (RB; MXB 1730-335) uniquely shows both Type I and Type II X-ray bursts. The origin of the latter is ill-understood but has been linked to magnetospheric gating of the accretion flow. We present a spectral analysis of simultaneous Swift, NuSTAR and XMM-Newton observations of the RB during its 2015 outburst. Although a broad Fe K line has been observed before, the high quality of our observations allows us to model this line using relativistic reflection models for the first time. We find that the disc is strongly truncated at 41.8^{+6.7}_{-5.3} gravitational radii (∼87 km), which supports magnetospheric Type II burst models and strongly disfavours models involving instabilities at the innermost stable circular orbit. Assuming that the RB magnetic field indeed truncates the disc, we find B = (6.2 ± 1.5) × 108 G, larger than typically inferred for NS LMXBs. In addition, we find a low inclination (i = 29° ± 2°). Finally, we comment on the origin of the Comptonized and thermal components in the RB spectrum.

  19. Flares in gamma-ray bursts: disc fragmentation and evolution

    NASA Astrophysics Data System (ADS)

    Dall'Osso, Simone; Perna, Rosalba; Tanaka, Takamitsu L.; Margutti, Raffaella

    2017-02-01

    Flaring activity following gamma-ray bursts (GRBs), observed in both long and short GRBs, signals a long-term activity of the central engine. However, its production mechanism has remained elusive. Here, we develop a quantitative model of the idea proposed by Perna et al. of a disc whose outer regions fragment due to the onset of gravitational instability. The self-gravitating clumps migrate through the disc and begin to evolve viscously when tidal and shearing torques break them apart. Our model consists of two ingredients: theoretical bolometric flare light curves whose shape (width, skewness) is largely insensitive to the model parameters, and a spectral correction to match the bandpass of the available observations, that is calibrated using the observed spectra of the flares. This simple model reproduces, with excellent agreement, the empirical statistical properties of the flares as measured by their width-to-arrival time ratio and skewness (ratio between decay and rise time). We present model fits to the observed light curves of two well-monitored flares, GRB 060418 and GRB 060904B. To the best of our knowledge, this is the first quantitative model able to reproduce the flare light curves and explain their global statistical properties.

  20. Mechanosignaling activation of TGFβ maintains intervertebral disc homeostasis

    PubMed Central

    Bian, Qin; Ma, Lei; Jain, Amit; Crane, Janet L; Kebaish, Khaled; Wan, Mei; Zhang, Zhengdong; Edward Guo, X; Sponseller, Paul D; Séguin, Cheryle A; Riley, Lee H; Wang, Yongjun; Cao, Xu

    2017-01-01

    Intervertebral disc (IVD) degeneration is the leading cause of disability with no disease-modifying treatment. IVD degeneration is associated with instable mechanical loading in the spine, but little is known about how mechanical stress regulates nucleus notochordal (NC) cells to maintain IVD homeostasis. Here we report that mechanical stress can result in excessive integrin αvβ6-mediated activation of transforming growth factor beta (TGFβ), decreased NC cell vacuoles, and increased matrix proteoglycan production, and results in degenerative disc disease (DDD). Knockout of TGFβ type II receptor (TβRII) or integrin αv in the NC cells inhibited functional activity of postnatal NC cells and also resulted in DDD under mechanical loading. Administration of RGD peptide, TGFβ, and αvβ6-neutralizing antibodies attenuated IVD degeneration. Thus, integrin-mediated activation of TGFβ plays a critical role in mechanical signaling transduction to regulate IVD cell function and homeostasis. Manipulation of this signaling pathway may be a potential therapeutic target to modify DDD. PMID:28392965