WorldWideScience

Sample records for intrapapillary disc colobomata

  1. Broken discs: warp propagation in accretion discs

    OpenAIRE

    Nixon, Chris; King, Andrew

    2012-01-01

    We simulate the viscous evolution of an accretion disc around a spinning black hole. In general any such disc is misaligned, and warped by the Lense-Thirring effect. Unlike previous studies we use effective viscosities constrained to be consistent with the internal fluid dynamics of the disc. We find that nonlinear fluid effects, which reduce the effective viscosities in warped regions, can promote the breaking of the disc into two distinct planes. This occurs when the Shakura & Sunyaev dimen...

  2. Dynamos in accretion discs

    OpenAIRE

    Brandenburg, A.; von Rekowski, B.

    2007-01-01

    It is argued that accretion discs in young stellar objects may have hot coronae that are heated by magnetic reconnection. This is a consequence of the magneto-rotational instability driving turbulence in the disc. Magnetic reconnection away from the midplane leads to heating of the corona which, in turn, contributes to driving disc winds.

  3. Black hole accretion discs

    CERN Document Server

    Lasota, Jean-Pierre

    2015-01-01

    This is an introduction to models of accretion discs around black holes. After a presentation of the non-relativistic equations describing the structure and evolution of geometrically thin accretion discs we discuss their steady-state solutions and compare them to observation. Next we describe in detail the thermal-viscous disc instability model and its application to dwarf novae for which it was designed and its X-ray irradiated-disc version which explains the soft X--ray transients, i.e. outbursting black-hole low-mass X-ray binaries. We then turn to the role of advection in accretion flow onto black holes illustrating its action and importance with a toy model describing both ADAFs and slim discs. We conclude with a presentation of the general-relativistic formalism describing accretion discs in the Kerr space-time.

  4. MHD disc winds

    CERN Document Server

    Ferreira, J

    2006-01-01

    This is a doctorate level lecture on the physics of accretion discs driving magnetically self-confined jets, usually referred to in the literature as disc winds. I will first review the governing magnetohydrodynamic equations and then discuss their physical content. At that level, necessary conditions to drive jets from keplerian accretion discs can already be derived. These conditions are validated with self-similar calculations of accretion-ejection structures. In a second part, I will critically discuss the biases introduced when using self-similarity as well as some other questions such as: Are these systems really unstable? Can a standard accretion disc provide the conditions to launch jets in its innermost parts? What is the difference between X-winds and disc-winds? Finally, the magnetic interaction between a protostar and its circumstellar disc will be discussed with a focus on stellar spin down.

  5. Black hole accretion discs

    OpenAIRE

    Lasota, Jean-Pierre

    2015-01-01

    This is an introduction to models of accretion discs around black holes. After a presentation of the non-relativistic equations describing the structure and evolution of geometrically thin accretion discs we discuss their steady-state solutions and compare them to observation. Next we describe in detail the thermal-viscous disc instability model and its application to dwarf novae for which it was designed and its X-ray irradiated-disc version which explains the soft X--ray transients, i.e. ou...

  6. Optic disc oedema

    DEFF Research Database (Denmark)

    Nielsen, Marianne Kromann; Hamann, Steffen

    2014-01-01

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

  7. Artificial Disc Replacement

    Science.gov (United States)

    ... Strengthening Strengthen Your Core! Stretching/Flexibility Aerobic Exercise Cervical ... disc is the soft cushioning structure located between the individual bones of the spine, called “vertebra.” It is made of cartilage-like tissue and ...

  8. Innervation of ''painful'' lumbar discs

    NARCIS (Netherlands)

    Coppes, MH; Marani, E; Thomeer, RTWM; Groen, GJ

    1997-01-01

    Study Design. The authors investigated the innervation of discographically confirmed degenerated and ''painful'' human intervertebral discs. Objective. To determine the type and distribution patterns of nerve fibers present in degenerated human intervertebral discs. Summary of Background Data. The i

  9. How do accretion discs break?

    Science.gov (United States)

    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.

  10. Tracing Planets in Circumstellar Discs

    Directory of Open Access Journals (Sweden)

    Uribe Ana L.

    2013-04-01

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

  11. Evolution of Protoplanetary Discs with Magnetically Driven Disc Winds

    CERN Document Server

    Suzuki, Takeru K; Morbidelli, Alessandro; Crida, Aurélien; Guillot, Tristan

    2016-01-01

    Aims: We investigate the evolution of protoplanetary discs (PPDs hereafter) with magnetically driven disc winds and viscous heating. Methods: We consider an initially massive disc with ~0.1 Msun to track the evolution from the early stage of PPDs. We solve the time evolution of surface density and temperature by taking into account viscous heating and the loss of the mass and the angular momentum by the disc winds within the framework of a standard alpha model for accretion discs. Our model parameters, turbulent viscosity, disc wind mass loss, and disc wind torque, which are 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 remaining, surface densities show a large variety, depending on the combinatio...

  12. Counter-Rotating Accretion Discs

    OpenAIRE

    Dyda, Sergei; Lovelace, Richard V. E.; Ustyugova, Galina V.; Romanova, Marina M.; Koldoba, Alexander V.

    2014-01-01

    Counter-rotating discs can arise from the accretion of a counter-rotating gas cloud onto the surface of an existing co-rotating disc or from the counter-rotating gas moving radially inward to the outer edge of an existing disc. At the interface, the two components mix to produce gas or plasma with zero net angular momentum which tends to free-fall towards the disc center. We discuss high-resolution axisymmetric hydrodynamic simulations of a viscous counter-rotating disc for cases where the tw...

  13. Vibration analysis of atomising discs

    Energy Technology Data Exchange (ETDEWEB)

    Deng, H; Ouyang, H, E-mail: H.Ouyang@liverpool.ac.u [Department of Engineering, University of Liverpool, Liverpool L69 3GH (United Kingdom)

    2009-08-01

    The centrifugal atomisation of metallic melts using a spinning disc is an important process for powder production and spray deposition. In the manufacturing process the high-temperature melt flows down to the surface of the atomising disc spinning at very high speed. It is observed that there is a hydraulic jump of the melt flow prior to atomisation. In this paper, the dynamic model of the atomising disc as a spinning Kirchhoff plate with this hydraulic jump is established. The flowing melt is modelled as moving mass and weight force in the radial direction. Using a Galerkin method, it is found that the vibration properties of the atomising disc vary with the disc clamping ratio. The amplitude of the vibration is largely raised when the clamping ratio is smaller than the critical jump radius ratio. It is also found that the disc vibration is non-stationary before becoming steady and the amplitude decreases with increasing disc speed.

  14. Discs in misaligned binary systems

    CERN Document Server

    Rawiraswattana, Krisada; Goodwin, Simon P

    2016-01-01

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

  15. Cervical Total Disc Arthroplasty

    OpenAIRE

    Basho, Rahul; Hood, Kenneth A.

    2012-01-01

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

  16. Accretion Discs in Blazars

    OpenAIRE

    Jolley, E. J. D.; Kuncic, Z.; Bicknell, G. V.; Wagner, S.(Max-Planck-Institut für Kernphysik, 69117, Heidelberg, Germany)

    2009-01-01

    The characteristic properties of blazars (rapid variability, strong polarization, high brightness) are widely attributed to a powerful relativistic jet oriented close to our line of sight. Despite the spectral energy distributions (SEDs) being strongly jet-dominated, a "big blue bump" has been recently detected in sources known as flat spectrum radio quasars (FSRQs). These new data provide a unique opportunity to observationally test coupled jet-disc accretion models in these extreme sources....

  17. Total disc replacement.

    Science.gov (United States)

    Vital, J-M; Boissière, L

    2014-02-01

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

  18. Apsidal precession, disc breaking and viscosity in warped discs

    CERN Document Server

    Nealon, Rebecca; Price, Daniel J; King, Andrew

    2015-01-01

    We demonstrate the importance of general relativistic apsidal precession in warped black hole accretion discs by comparing three - dimensional smoothed particle hydrodynamic simulations in which this effect is first neglected, and then included. If apsidal precession is neglected, we confirm the results of an earlier magnetohydrodynamic simulation which made this assumption, showing that at least in this case the $\\alpha$ viscosity model produces very similar results to those of simulations where angular momentum transport is due to the magnetorotational instability. Including apsidal precession significantly changes the predicted disc evolution. For moderately inclined discs thick enough that tilt is transported by bending waves, we find a disc tilt which is nonzero at the inner disc edge and oscillates with radius, consistent with published analytic results. For larger inclinations we find disc breaking.

  19. Mechanics of Actuated Disc Cutting

    Science.gov (United States)

    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.

  20. Estrogens and the intervertebral disc.

    Science.gov (United States)

    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.

  1. Heat distribution in disc brake

    Science.gov (United States)

    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.

  2. Dynamics of warped accretion discs

    OpenAIRE

    Tremaine, Scott; Davis, Shane W.

    2013-01-01

    Accretion discs are present around both stellar-mass black holes in X-ray binaries and supermassive black holes in active galactic nuclei. A wide variety of circumstantial evidence implies that many of these discs are warped. The standard Bardeen--Petterson model attributes the shape of the warp to the competition between Lense--Thirring torque from the central black hole and viscous angular-momentum transport within the disc. We show that this description is incomplete, and that torques from...

  3. Numbered nasal discs for waterfowl

    Science.gov (United States)

    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.

  4. Optic disc drusen

    DEFF Research Database (Denmark)

    Fledelius, Hans C

    2017-01-01

    PURPOSE: To examine long-term data on optic disc drusen (ODD) from an outpatient hospital series that indicated more cases with advanced visual field constriction than is apparent from other clinical reports. The underlying pathophysiology is discussed, also with regard to enlarged blind spot...... neurosurgery for an arachnoid cyst. CONCLUSIONS: We found more cases of marked visual field constriction than reported in other clinical series. A few such cases appeared acute and vascular, but the main trend was clinically quiet over time. All 49 patients could manage visually in daily life....

  5. [Temporomandibular joint disc surgery].

    Science.gov (United States)

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

    2016-09-01

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

  6. Relativistic Disc lines

    CERN Document Server

    Fabian, A C; Parker, M L

    2014-01-01

    Broad emission lines, particularly broad iron-K lines, are now commonly seen in the X-ray spectra of luminous AGN and Galactic black hole binaries. Sensitive NuSTAR spectra over the energy range of 3-78 keV and high frequency reverberation spectra now confirm that these are relativistic disc lines produced by coronal irradiation of the innermost accretion flow around rapidly spinning black holes. General relativistic effects are essential in explaining the observations. Recent results are briefly reviewed here.

  7. Accretion discs trapped near corotation

    NARCIS (Netherlands)

    D'Angelo, C.R.; Spruit, H.C.

    2012-01-01

    We show that discs accreting on to the magnetosphere of a rotating star can end up in a trapped state, in which the inner edge of the disc stays near the corotation radius, even at low and varying accretion rates. The accretion in these trapped states can be steady or cyclic; we explore these states

  8. Intraoral micro-identification discs.

    Science.gov (United States)

    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.

  9. Evolution of protoplanetary discs with magnetically driven disc winds

    Science.gov (United States)

    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 migration of protoplanets. Conclusions: The variety of our calculated PPDs should yield a wide variety of exoplanet systems.

  10. Coevolution of Binaries and Gaseous Discs

    CERN Document Server

    Fleming, David P

    2016-01-01

    The recent discoveries of circumbinary planets by $\\it Kepler$ 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 that 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 (SPH) simulations of gaseous protoplanetary discs surrounding binaries based on Kepler 38 were run for $10^4$ 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 eccentri...

  11. Accretion discs trapped near corotation

    OpenAIRE

    D'Angelo, C.R.; Spruit, H.C.

    2012-01-01

    We show that discs accreting on to the magnetosphere of a rotating star can end up in a trapped state, in which the inner edge of the disc stays near the corotation radius, even at low and varying accretion rates. The accretion in these trapped states can be steady or cyclic; we explore these states over a wide range of parameter space. We find two distinct regions of instability: one related to the buildup and release of mass in the disc outside corotation, and the other to mass storage with...

  12. Eclipse mapping of accretion discs

    CERN Document Server

    Baptista, R

    2000-01-01

    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 through 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.

  13. Vortex migration in protoplanetary discs

    Directory of Open Access Journals (Sweden)

    Papaloizou John C. B.

    2013-04-01

    Full Text Available Vortices embedded in protoplanetary discs can act as obstacles to the unperturbed disc flow. The resulting velocity perturbations propagate away from the vortex in the form of density waves that transport angular momentum. Any asymmetry between the inner and the outer density wave means that the region around the vortex has to change its angular momentum. We find that this leads to orbital migration of the vortex. Asymmetric waves always arise except in the case of a disc with constant pressure, for isothermal as well as non-isothermal discs. Depending on the size and strength of the vortex, the resulting migration time scales can be as short as a few thousand orbits.

  14. Modelling Neutral Hydrogen Discs of Spiral Galaxies

    Institute of Scientific and Technical Information of China (English)

    林伟鹏; 洪碧海

    2002-01-01

    We present an analytical model of a neutral hydrogen disc in a spiral galaxy. The gas disc of the spiral galaxy isassumed to have an exponential surface density profile and to be ionized by the cosmic ultraviolet background.To compare with observations, we consider the disc position angle and inclination angle for a line of sight goingthrough the galaxy disc. The HI column densities depend on the strength of ionizing field and disc position andinclination. The model was applied to NGC 3198 and the results were compared with observational data. TheHI disc profile at large disc radii can be tested by further HI observations using radio telescopes with a largeraperture than the present facilities. This HI disc model can be used to predict quasar absorption line systems bygalaxy discs if quasar lines of sight go through the discs.

  15. Debris disc formation induced by planetary growth

    CERN Document Server

    Kobayashi, Hiroshi

    2014-01-01

    Several hundred stars older than 10 million years have been observed to have infrared excesses. These observations are explained by dust grains formed by the collisional fragmentation of hidden planetesimals. Such dusty planetesimal discs are known as debris discs. In a dynamically cold planetesimal disc, collisional coagulation of planetesimals produces planetary embryos which then stir the surrounding leftover planetesimals. Thus, the collisional fragmentation of planetesimals that results from planet formation forms a debris disc. We aim to determine the properties of the underlying planetesimals in debris discs by numerically modelling the coagulation and fragmentation of planetesimal populations. The brightness and temporal evolution of debris discs depend on the radial distribution of planetesimal discs, the location of their inner and outer edges, their total mass, and the size of planetesimals in the disc. We find that a radially narrow planetesimal disc is most likely to result in a debris disc that ...

  16. Photon Bubbles in Accretion Discs

    OpenAIRE

    Gammie, Charles F.

    1998-01-01

    We show that radiation dominated accretion discs are likely to suffer from a ``photon bubble'' instability similar to that described by Arons in the context of accretion onto neutron star polar caps. The instability requires a magnetic field for its existence. In an asymptotic regime appropriate to accretion discs, we find that the overstable modes obey the remarkably simple dispersion relation \\omega^2 = -i g k F(B,k). Here g is the vertical gravitational acceleration, B the magnetic field, ...

  17. Self-gravitating accretion discs

    OpenAIRE

    Lodato, G.

    2008-01-01

    I review recent progresses in the dynamics and the evolution of self-gravitating accretion discs. Accretion discs are a fundamental component of several astrophysical systems on very diverse scales, and can be found around supermassive black holes in Active Galactic Nuclei (AGN), and also in our Galaxy around stellar mass compact objects and around young stars. Notwithstanding the specific differences arising from such diversity in physical extent, all these systems share a common feature whe...

  18. Disc piezoelectric ceramic transformers.

    Science.gov (United States)

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

    2013-08-01

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

  19. Resonances in retrograde circumbinary discs

    CERN Document Server

    Nixon, Chris

    2015-01-01

    We analyse the interaction of an eccentric binary with a circular coplanar circumbinary disc that rotates in a retrograde sense with respect to the binary. In the circular binary case, no Lindblad resonances lie within the disc and no Lindblad resonant torques are produced, as was previously known. By analytic means, we show that when the binary orbit is eccentric, there exist components of the gravitational potential of the binary which rotate in a retrograde sense to the binary orbit and so rotate progradely with respect to this disc, allowing a resonant interaction to occur between the binary and the disc. The resulting resonant torques distinctly alter the disc response from the circular binary case. We describe results of three-dimensional hydrodynamic simulations to explore this effect and categorise the response of the disc in terms of modes whose strengths vary as a function of binary mass ratio and eccentricity. These mode strengths are weak compared to the largest mode strengths expected in the prog...

  20. Lumbar disc excision through fenestration

    Directory of Open Access Journals (Sweden)

    Sangwan S

    2006-01-01

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

  1. Counter-Rotating Accretion Discs

    CERN Document Server

    Dyda, Sergei; Ustyugova, Galina V; Romanova, Marina M; Koldoba, Alexander V

    2014-01-01

    Counter-rotating discs can arise from the accretion of a counter-rotating gas cloud onto the surface of an existing co-rotating disc or from the counter-rotating gas moving radially inward to the outer edge of an existing disc. At the interface, the two components mix to produce gas or plasma with zero net angular momentum which tends to free-fall towards the disc center. We discuss high-resolution axisymmetric hydrodynamic simulations of a viscous counter-rotating disc for cases where the two components are vertically separated and radially separated. The viscosity is described by an isotropic $\\alpha-$viscosity including all terms in the viscous stress tensor. For the vertically separated components a shear layer forms between them. The middle of this layer free-falls to the disk center. The accretion rates are increased by factors $\\sim 10^2-10^4$ over that of a conventional disc rotating in one direction with the same viscosity. The vertical width of the shear layer and the accretion rate are strongly dep...

  2. Prosthetic Lumbar disc replacement for degenerative disc disease

    Directory of Open Access Journals (Sweden)

    Kulkarni Arvind

    2005-01-01

    Full Text Available Mechanical articulated device to replace intervertebral disc as a treatment for low back pain secondary to disc degeneration has emerged as a promising tool for selected patients. The potential advantages are prevention of adjacent segment degeneration, maintenance of mobility as well as avoidance of all the complications associated with fusion. The short-term results have been comparable to that of fusion, a few mid-term results have shown mixed outcome, but information on long-term results and performance are not available at present. The rationale for lumbar disc arthroplasty, indications, contraindications, the various artificial devices in the market and the concepts intrinsic to each of them, basic technique of insertion, complications are discussed and a brief summary of our experience with one of the devices is presented.

  3. Analyses of the temporomandibular disc.

    Science.gov (United States)

    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.

  4. Black hole accretion disc impacts

    CERN Document Server

    Pihajoki, Pauli

    2015-01-01

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

  5. Atomic gas in debris discs

    Science.gov (United States)

    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.

  6. Coevolution of binaries and circumbinary gaseous discs

    Science.gov (United States)

    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.

  7. Vertebral osteomyelitis without disc involvement

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-10-01

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

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

    Directory of Open Access Journals (Sweden)

    D’Angelo Caroline

    2014-01-01

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

  9. Photoevaporating transitional discs and molecular cloud cores

    Science.gov (United States)

    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.

  10. Radiation of accretion discs: the eclipses

    Energy Technology Data Exchange (ETDEWEB)

    Schwarzenberg-Czerny, A.

    1984-05-01

    Light curves have been calculated for eclipses of the accretion disc in a cataclysmic binary. The Roche geometry of the cool component was taken into account and the stellar atmospheres were interpolated to provide the local spectrum of the radiation from the disc. The dependence of the light curve on the parameters of the disc is discussed.

  11. Intervertebral disc degeneration in dogs

    NARCIS (Netherlands)

    Bergknut, Niklas

    2011-01-01

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

  12. Electromagnetic Levitation of a Disc

    Science.gov (United States)

    Valle, R.; Neves, F.; de Andrade, R., Jr.; Stephan, R. M.

    2012-01-01

    This paper presents a teaching experiment that explores the levitation of a disc of ferromagnetic material in the presence of the magnetic field produced by a single electromagnet. In comparison to the classical experiment of the levitation of a sphere, the main advantage of the proposed laboratory bench is that the uniform magnetic field…

  13. Optical Disc Applications in Libraries.

    Science.gov (United States)

    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…

  14. Electromagnetic Levitation of a Disc

    Science.gov (United States)

    Valle, R.; Neves, F.; de Andrade, R., Jr.; Stephan, R. M.

    2012-01-01

    This paper presents a teaching experiment that explores the levitation of a disc of ferromagnetic material in the presence of the magnetic field produced by a single electromagnet. In comparison to the classical experiment of the levitation of a sphere, the main advantage of the proposed laboratory bench is that the uniform magnetic field…

  15. Constraints on Slim Accretion Discs

    Institute of Scientific and Technical Information of China (English)

    CAI Zhen-Yi; GU Wei-Min; LU Ju-Fu

    2008-01-01

    @@ We show that when the gravitational force in the vertical direction is correctly calculated, the well-known Sshaped sequence of thermal equilibrium solutions can be constructed only for small radii of black hole accretion flows, such that slim accretion discs can possibly exist only in the inner regions of these flows.

  16. Magnetorotational instability in protoplanetary discs

    CERN Document Server

    Salmeron, Roberto Aureliano; Salmeron, Raquel; Wardle, Mark

    2004-01-01

    We investigate the linear growth and vertical structure of the magnetorotational instability (MRI) in weakly ionised, stratified accretion discs. The magnetic field is initially vertical and dust grains are assumed to have settled towards the midplane, so charges are carried by electrons and ions only. Solutions are obtained at representative radial locations from the central protostar for different choices of the initial magnetic field strength, sources of ionisation, and disc surface density. The MRI is active over a wide range of magnetic field strengths and fluid conditions in low conductivity discs. For the minimum-mass solar nebula model, incorporating cosmic ray ionisation, perturbations grow at 1 AU for B < 8 G. For a significant subset of these strengths (0.2 - 5 G), the growth rate is of order the ideal MHD rate (0.75 Omega). Similarly, when cosmic rays are assumed to be excluded from the disc by the winds emitted by the magnetically active protostar, unstable modes grow at this radius for B less...

  17. Medium-term outcomes of artificial disc replacement for severe cervical disc narrowing

    Directory of Open Access Journals (Sweden)

    Chao-Hung Yeh

    2014-01-01

    Conclusions: Acceptable clinical outcome for treatment of severe cervical disc narrowing with cervical disc replacement technique has been performed in current study. Most patients maintained good postoperative mobility and no significant adjacent level degeneration were found. Cervical disc replacement may be applicable in treatment of severe cervical disc narrowing; however, longer follow-ups are required for ensuring the long-term efficacy of cervical disc replacement.

  18. Intervertebral disc calcifications in children.

    Science.gov (United States)

    Beluffi, G; Fiori, P; Sileo, C

    2009-03-01

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

  19. Disc degeneration: current surgical options

    Directory of Open Access Journals (Sweden)

    C Schizas

    2010-10-01

    Full Text Available Chronic low back pain attributed to lumbar disc degeneration poses a serious challenge to physicians. Surgery may be indicated in selected cases following failure of appropriate conservative treatment. For decades, the only surgical option has been spinal fusion, but its results have been inconsistent. Some prospective trials show superiority over usual conservative measures while others fail to demonstrate its advantages. In an effort to improve results of fusion and to decrease the incidence of adjacent segment degeneration, total disc replacement techniques have been introduced and studied extensively. Short-term results have shown superiority over some fusion techniques. Mid-term results however tend to show that this approach yields results equivalent to those of spinal fusion. Nucleus replacement has gained some popularity initially, but evidence on its efficacy is scarce. Dynamic stabilisation, a technique involving less rigid implants than in spinal fusion and performed without the need for bone grafting, represents another surgical option. Evidence again is lacking on its superiority over other surgical strategies and conservative measures. Insertion of interspinous devices posteriorly, aiming at redistributing loads and relieving pain, has been used as an adjunct to disc removal surgery for disc herniation. To date however, there is no clear evidence on their efficacy. Minimally invasive intradiscal thermocoagulation techniques have also been tried, but evidence of their effectiveness is questioned. Surgery using novel biological solutions may be the future of discogenic pain treatment. Collaboration between clinicians and basic scientists in this multidisciplinary field will undoubtedly shape the future of treating symptomatic disc degeneration.

  20. Planetary migration in weakly magnetized turbulent discs

    Science.gov (United States)

    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.

  1. Radiation from optically thin accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Tylenda, R. (Polska Akademia Nauk, Torun. Pracownia Astrofizyki)

    1981-01-01

    Accretion discs in cataclysmic variables with low rates of mass transfer, M < or approx. 10/sup 16/g s/sup -1/, have outer regions optically thin in continuum. A simple approach that allows one to calculate the radiation spectra from such discs is presented. A great number of disc models has been obtained in order to study the influence of various parameters (accretion rate, outer radius of the disc, inclination angle, mass of the accreting degenerate dwarf, viscosity parameter) of discs on the outgoing continuous spectra, emission lines and the UBV colours.

  2. The artificial disc: theory, design and materials.

    Science.gov (United States)

    Bao, Q B; McCullen, G M; Higham, P A; Dumbleton, J H; Yuan, H A

    1996-06-01

    Low back pain is one of the most common medical conditions in the Western world. Disc degeneration, an inevitable process of aging, of variable rate and degree, is one of the major causes of low back pain. Currently, there are two major surgical interventions for treating conditions related to the degenerative disc: discectomy and fusion. Although discectomy and fusion produce a relatively good short-term clinical result in relieving pain, both these surgical treatments alter the biomechanics of the spine, possibly leading to further degeneration of the surrounding tissues and the discs at adjacent levels. Over the past 35 years, a tremendous effort has been made to develop an artificial disc to replace the degenerated disc. The goal is the restoration of the natural biomechanics of the segment after disc excision, thus relieving pain and preventing further degeneration at adjacent segments. However, the artificial disc faces a complex biomechanical environment which makes replication of the biomechanics difficult and long-term survival challenging to designs and materials. The purpose of this article is to examine the factors of importance in designing a disc replacement. Topics covered include the structure and function of the natural disc, the changes that occur with disc degeneration and existing methods of treatment for the degenerative spine. The progress in achieving a functional, long-lasting disc replacement is outlined.

  3. The properties of external accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Pringle, J.E. (Space Telescope Science Inst., Baltimore, MD (USA))

    1991-02-15

    The properties of external accretion discs (discs with a central source of angular momentum) are explored both analytically and numerically. An illustrative example of the effect of a disc of material around a binary star on the stellar separation is considered. We consider a Greens-function-type solution in which an initial ring of matter is put in orbit around the central binary. We find that the solution splits temporally into three parts. First, the disc evolves as a standard accretion disc unaware of the inner boundary condition. Secondly, the disc interacts with the inner boundary and changes its character to become, thirdly, an outflowing disc which is propelled outwards by the source of angular momentum at the centre. (author).

  4. Twisted accretion discs: Pt. 5; Viscous evolution

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, S. (Max-Planck-Institut fuer Physik und Astrophysik, Garching (Germany, F.R.). Inst. fuer Astrophysik)

    1990-08-15

    The time-dependence of accretion discs with orbits tilted out of the symmetry plane is studied. The effects of mass inflow modulation, and tilt variation at the disc outer edge, are examined for both circumbinary discs and for discs around compact objects. The appendices extend the numerical work to some analytic examples of tilt diffusion and external forcing effects. It is also shown that the disc must not be treated as a rigid tilted object if global angular momentum is to be conserved. These results are relevant to the problem of long-term periodicities of the light curves in Her X1 and {epsilon} Aur, the S-type symmetry of radio jets, warped gas discs in galaxies and polar rings in Neptune. Twisted discs may also arise in star-forming regions. (author).

  5. Three-level cervical disc herniation

    Directory of Open Access Journals (Sweden)

    St. Iencean Andrei

    2015-09-01

    Full Text Available Multilevel cervical degenerative disc disease is well known in the cervical spine pathology, with radicular syndromes or cervical myelopathy. One or two level cervical herniated disc is common in adult and multilevel cervical degenerative disc herniation is common in the elderly, with spinal stenosis, and have the same cause: the gradual degeneration of the disc. We report the case of a patient with two level cervical disc herniation (C4 – C5 and C5 – C6 treated by anterior cervical microdiscectomy both levels and fusion at C5 – C6; after five years the patient returned with left C7 radiculopathy and MRI provided the image of a left C6 – C7 disc herniation, he underwent an anterior microsurgical discectomy with rapid relief of symptoms. Three-level cervical herniated disc are rare in adults, and the anterior microdiscectomy with or without fusion solve this pathology.

  6. Centrifugally exhausting discs: an inverse process of disc-like accretion

    Energy Technology Data Exchange (ETDEWEB)

    Kaburaki, O.

    1989-03-01

    A disc-like mass-loss process from rapidly rotating, highly magnetized objects is investigated. Such a disc may be considered as an inverse-type of magnetized accretion discs. The disc plasma flows out radially with the Alfven velocity while it rotates, in the main part of the disc, with Keplerian velocity. The magnetic stress transfers angular momentum from the central spinner to the disc. A considerable fraction of the rotational energy extracted in association with the angular momentum is liberated in the disc through the (effective) Joule dissipation. An almost self-consistent set of analytic expressions is proposed as a solution to the steady-state, resistive MHD equations which are fairly simplified by the assumption of thin disc. The possibility of finding such discs around young neutron stars is briefly discussed with reference to SN 1987A.

  7. Grain charging in protoplanetary discs

    CERN Document Server

    Ilgner, Martin

    2011-01-01

    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 MHD (magnetohydrodynamic) turbulence and grain growth which are coupled in a two-way process. 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 D_f = 2. 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. The results show that the adsorption/desorption of neutral gas-phase heavy metals, such as magnesium, effects the ...

  8. Superhumps, resonances and accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Whitehurst, R.; King, A. (Leicester Univ. (UK). Dept. of Astronomy)

    1991-03-01

    The structure of accretion discs within binary systems is shown to be influenced by the excitation of resonances within the disc. Of particular importance is that near the 3:1 commensurability with the stars' orbit. This can be used to explain the superhump phenomenon of SU Ursae Majoris dwarf novae in superoutburst. This resonance can only appear for mass ratios which satisfy M{sub 2}/M{sub 1} < {approx equal} 0.25-0.33: for larger mass ratios the available resonances are weaker and of the wrong form to produce the superhump phenomenon. The mass-transfer stream is shown to be an important contributor to the growth rate of the resonance. (author).

  9. Eclipse mapping of accretion discs

    OpenAIRE

    Baptista, Raymundo

    2000-01-01

    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 dist...

  10. The dispersal of protoplanetary discs

    Directory of Open Access Journals (Sweden)

    Ercolano Barbara

    2013-04-01

    Full Text Available Protoplanetary discs are a natural consequence of the star formation process and as such are ubiquitous around low-mass stars. They are fundamental to planet formation as they hold the reservoir of material from which planets form. Their evolution and final dispersal and the timescales that regulate these process are therefore of particular interest. In this contribution I will review the observational evidence for the dispersal of discs being dominated by two timescales and for the final dispersal to occur quickly and from the inside out. I will discuss the current theoretical models, including X-ray photoevaporation, showing that the latter provides a natural explanation to the observed behaviour and review supporting and contrasting evidence. I will finally introduce a new mechanism based on the interaction between planet formation and photoevaporation that may explain a particular class of transition discs with large inner holes and high accretion rates that are problematic for photoevaporation models and planet formation models alone.

  11. Biomechanical study of intervertebral disc degeneration

    OpenAIRE

    González Guitiérrez, Ramiro Arturo

    2012-01-01

    Degeneration and age affect the biomechanics of the intervertebral disc, by reducing its stiffness, flexibility and shock absorption capacities against daily movement and spinal load. The biomechanical characterization of intervertebral discs is achieved by conducting mechanical testing to vertebra-disc-vertebra segments and applying axial, shear, bend and torsion loads, statically or dynamically, with load magnitudes corresponding to the physiological range. However, traditional testing does...

  12. DSC Study of Collagen in Disc Disease

    OpenAIRE

    S. Skrzyński; Sionkowska, A.; Marciniak, A.

    2009-01-01

    Differential scanning calorimetry (DSC) has been used to estimate the effect of disc disease on the collagen helix-coil transition and morphology for tissue extracted from patients during surgical operation. Forty discs were obtained from patients with degenerative disc disease undergoing surgery for low back pain. The patients were in the age between 20 and 70 years old. The specimens were kept wet during DSC experiment. The data allow the comparison between thermal stability of collagen ti...

  13. Biomechanical study of intervertebral disc degeneration

    OpenAIRE

    González Guitiérrez, Ramiro Arturo

    2012-01-01

    Degeneration and age affect the biomechanics of the intervertebral disc, by reducing its stiffness, flexibility and shock absorption capacities against daily movement and spinal load. The biomechanical characterization of intervertebral discs is achieved by conducting mechanical testing to vertebra-disc-vertebra segments and applying axial, shear, bend and torsion loads, statically or dynamically, with load magnitudes corresponding to the physiological range. However, traditional testing does...

  14. The Roles of Discs for Planetary Systems

    CERN Document Server

    Yeh, L C; Yeh, Li-Chin; Jiang, Ing-Guey

    2007-01-01

    It is known that the discs are detected for some of the extra-solar planetary systems. It is also likely that there was a disc mixing with planets and small bodies while our Solar System was forming. From our recent results, we conclude that the discs play two roles: the gravity makes planetary systems more chaotic and the drag makes planetary systems more resonant.

  15. DISC1 genetics, biology and psychiatric illness

    OpenAIRE

    2013-01-01

    Psychiatric disorders are highly heritable, and in many individuals likely arise from the combined effects of genes and the environment. A substantial body of evidence points towards DISC1 being one of the genes that influence risk of schizophrenia, bipolar disorder and depression, and functional studies of DISC1 consequently have the potential to reveal much about the pathways that lead to major mental illness. Here, we review the evidence that DISC1 influences disease risk through effects u...

  16. The quiescent phase of galactic disc growth

    Science.gov (United States)

    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.

  17. Accretion Discs Show Their True Colours

    Science.gov (United States)

    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

  18. DSC Study of Collagen in Disc Disease

    Directory of Open Access Journals (Sweden)

    S. Skrzyński

    2009-01-01

    Full Text Available Differential scanning calorimetry (DSC has been used to estimate the effect of disc disease on the collagen helix-coil transition and morphology for tissue extracted from patients during surgical operation. Forty discs were obtained from patients with degenerative disc disease undergoing surgery for low back pain. The patients were in the age between 20 and 70 years old. The specimens were kept wet during DSC experiment. The data allow the comparison between thermal stability of collagen tissue from healthy patients and from patients suffering from disc disease. In the paper the comparison between thermal helix-coil transition for collagen fibers from patients suffering from disc disease and collagen fibers from healthy organisms has been discussed. The heating rate has an influence on the position on denaturation temperatures of collagen in disc tissues. Higher helix-coil transition temperature of collagen in degenerated disc suggests that additional intermolecular cross linking of collagen fibers occurs. Denaturation temperatures of collagen in degenerated male disc possess smaller values than in female ones. Disc disease induces changes in collagen structure and leads to formation of additional crosslinks between collagen fibers.

  19. Computing Decoupled Residuals for Compact Disc Players

    DEFF Research Database (Denmark)

    Odgaard, Peter Fogh; Stoustrup, Jakob; Andersen, Palle

    2006-01-01

    In order to improve Compact Disc Players playability regarding playing Compact Discs with surface faults, like scratches and fingerprints etc, the attention has been put on fault tolerant control schemes. Almost every of those methods are based on fault detection. The standard approach is to use...... a pair of residuals generated by Compact Disc Player. However, these residuals depend on the performance of position servos in the Compact Disc Player. In other publications of the same authors a pair of decoupled residuals is derived. However, the computation of these alternative residuals has been...

  20. Evolution of linear warps in accretion discs and applications to protoplanetary discs in binaries

    CERN Document Server

    Foucart, Francois

    2014-01-01

    The existence of warped accretion discs is expected in a wide variety of astrophysical systems, including circumstellar discs in binaries and discs around binary protostars. A common feature of these discs is that they are perturbed by a misaligned external potential. In this paper, we study the long-term evolution of the disc warp and precession in the case of thick discs (with the dimensionless thickness $H/r$ larger than the viscosity parameter $\\alpha$) in which bending waves can propagate. For small warps, such discs undergo approximately rigid-body precession with a coherent global frequency. We derive the analytical expressions for the warp/twist profiles of the disc and the alignment timescale for a variety of disc models/parameters. Applying our results to circumbinary discs, we find that these discs align with the orbital plane of the binary on a timescale comparable to the global precession time of the disc, and typically much smaller than its viscous timescale. The development of parametric instab...

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

    Science.gov (United States)

    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.

  2. [Standardized terminology for disc disease].

    Science.gov (United States)

    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.

  3. Minimum weight design of inhomogeneous rotating discs

    Energy Technology Data Exchange (ETDEWEB)

    Jahed, Hamid [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of); Farshi, Behrooz [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of)]. E-mail: farshi@iust.ac.ir; Bidabadi, Jalal [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of)

    2005-01-01

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

  4. Methodology for optic disc localization

    Directory of Open Access Journals (Sweden)

    Marcos A. Leiva-Vasconcellos

    2014-04-01

    Full Text Available The use of digital images in many areas of society is an activity that has reached a remarkable growth in recent years mainly due to the great development that has occurred in technology around the world. These images have a great use in many branches of medicine because they facilitate the diagnosis by specialists and thus help patients to be diagnosed long before symptoms of the disease begin to manifest. For Ophthalmology, one of the most used images are the digital retinography, If it is used properly will allow the occurrence of eye diseases such as glaucoma and diabetic retinopathy. One of the main elements shown on retinal images are the optic disc, the location and detection is of vital importance for working with different parts of the structure o f the eye. This paper proposes two techniques for locating the optic disc in retinal images based on the combination of multiple filters and applying logical operators. To test the algorithms diaretDB0v11 and DRIVE database were used , as a result of the tests are correctly located the 99.091 % of the images from both repo sitories, and were successfully detected 85 % and 87.143 % of images of DRIVE database and diaretDB0v11 respectively.

  5. A Simulation Model of Focus and Radial Servos in Compact Disc Players with Disc Surface Defects

    DEFF Research Database (Denmark)

    Odgaard, Peter Fogh; Stoustrup, Jakob; Andersen, Palle

    2004-01-01

    Compact Disc players have been on the market in more than two decades.As a consequence most of the control servo problems have been solved. A large remaining problem to solve is the handling of Compact Discs with severe surface defects like scratches and fingerprints. This paper introduces a method...... for making the design of controllers handling surface defects easier. A simulation model of Compact Disc players playing discs with surface defects is presented. The main novel element in the model is a model of the surface defects. That model is based on data from discs with surface defects. This model...

  6. Post-Main Sequence Evolution of Debris Discs

    OpenAIRE

    Bonsor, Amy; Wyatt, Mark

    2010-01-01

    The population of debris discs on the main sequence is well constrained, however very little is known about debris discs around evolved stars. In this work we provide a theoretical framework that considers the effects of stellar evolution on debris discs; firstly considering the evolution of an individual disc from the main sequence through to the white dwarf phase, then extending this to the known population of debris discs around main sequence A stars. It is found that discs around evolved ...

  7. Thin, thick and dark discs in LCDM

    CERN Document Server

    Read, J I; Agertz, O; Debattista, Victor P

    2008-01-01

    In a LCDM cosmology, the Milky Way accretes satellites into the stellar disc. We use cosmological simulations to assess the frequency of near disc plane and higher inclination accretion events, and collisionless simulations of satellite mergers to quantify the final state of the accreted material and the effect on the thin disc. On average, a Milky Way-sized galaxy has 1.5 subhalos with vmax>80km/s; 5 with vmax>60km/s; and 13 with vmax>40km/s merge at redshift z>1. A third of these merge at an impact angle 20 degrees) are twice as likely as low inclination ones. These lead to structures that closely resemble the recently discovered inner/outer stellar halos. They also do more damage to the Milky Way stellar disc creating a more pronounced flare, and warp; both long-lived and consistent with current observations. The most massive mergers (vmax > 80km/s) heat t he thin disc enough to produce a thick disc. These heated thin disc stars are essential for obtaining a thick disc as massive as that seen in the Milky ...

  8. Hygroviscoelasticity of the Human Intervertebral Disc.

    Science.gov (United States)

    1980-07-01

    hernia - tion with age depends on the biochemical changes that occur in the material of the disc during its maturation process. However, a careful machanics...EFFORT One of the recurring pieces of information required in disc response is the intra- discal pressure when the spine is loaded axially. This

  9. Hydromagnetic Flow between Two Rotating Coaxial Discs

    Directory of Open Access Journals (Sweden)

    Abdul Aleem Khan

    1970-01-01

    Full Text Available This paper relates to the steady flow of an electrically incompressible viscous fluid between two parallel coaxial rotating discs with a transverse magnetic field when the discs are rotating in the same direction with the same velocity and there is a source at the centre.

  10. Genetic association studies in lumbar disc degeneration

    DEFF Research Database (Denmark)

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

    2012-01-01

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

  11. Requirements for an artificial intervertebral disc

    NARCIS (Netherlands)

    Eijkelkamp, MF; van Donkelaar, CC; Veldhuizen, AG; van Horn, [No Value; Huyghe, JM; Verkerke, GJ

    Intervertebral disc degeneration is an important social and economic problem. Presently available artificial intervertebral discs (AIDs) are insufficient and the main surgical intervention is still spinal fusion. The objective of the present study is to present a list of requirements for the

  12. Feature Based Control of Compact Disc Players

    DEFF Research Database (Denmark)

    Odgaard, Peter Fogh

    Two servo control loops are used to keep the Optical Pick-up Unit focused and radially on the information track of the Compact Disc. These control servos have problems handling surface faults on the Compact Disc. In this Ph.D thesis a method is proposed to improve the handling of these surface...

  13. The inner cavity of the circumnuclear disc

    Science.gov (United States)

    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.

  14. The maximum rotation of a galactic disc

    NARCIS (Netherlands)

    Bottema, R

    1997-01-01

    The observed stellar velocity dispersions of galactic discs show that the maximum rotation of a disc is on average 63% of the observed maximum rotation. This criterion can, however, not be applied to small or low surface brightness (LSB) galaxies because such systems show, in general, a continuously

  15. On the reliability of protostellar disc mass measurements and the existence of fragmenting discs

    CERN Document Server

    Dunham, Michael M; Arce, Héctor G

    2014-01-01

    We couple non-magnetic, hydrodynamical simulations of collapsing protostellar cores with radiative transfer evolutionary models to generate synthetic observations. We then use these synthetic observations to investigate the extent to which a simple method for measuring protostellar disc masses used in the literature recovers the intrinsic masses of the discs formed in the simulations. We evaluate the effects of contamination from the surrounding core, partially resolving out the disc, optical depth, fixed assumed dust temperatures, inclination, and the dust opacity law. We show that the combination of these effects can lead to disc mass underestimates by up to factors of 2-3 at millimeter wavelengths and up to an order of magnitude or larger at submillimeter wavelengths. The optically thin portions of protostellar discs are generally cooler in the Class I stage than the Class 0 stage since Class I discs are typically larger and more optically thick, and thus more shielded. The observed disc mass distribution ...

  16. Twisted accretion discs: Pt. 4. Alignment in polytropic discs and low. cap alpha. limit

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, S.

    1988-07-01

    Twisted thin accretion discs are of interest in explaining long-term periodicities in X-ray binaries, the eclipse in Epsilon Aurigae, and perhaps precessing radio jets and possible warped molecular outflows in star-forming regions. Earlier results used isothermal discs to determine the alignment radius, Rsub(a). Now we see how polytropic discs effect earlier results for discs around compact objects and around close binaries. We find that Rsub(a) for polytropic discs can be up to an order of magnitude larger, depending on the polytropic index, the viscosity parameter and the precession mechanism. There is little change in the earlier conclusion that the case for alignment in Her X-1 is marginal, while there is substantial alignment in epsilon Aur. A lower limit is put on ..cap alpha.. for isothermal discs, which is expected to hold for polytropic discs as well. A bound is put on the energy of the perturbed flows.

  17. About detection of precessing circumpulsar discs

    Science.gov (United States)

    Grimani, Catia

    2016-08-01

    Detections of circumpulsar discs and planetary systems through electromagnetic observations appear quite rare. In the case of PSR 1931+24 and B0656+14, the hypothesis of a precessing disc penetrating the pulsar light cylinder is found consistent with radio and gamma observations from these stars. Disc self-occultation and precession may affect electromagnetic measurements. We investigate here under which conditions gravitational waves generated by circumpulsar disc precession may be detected by the proposed second-generation space interferometers DECI-hertz Interferometer Gravitational Wave Observatory and Big Bang Observer. The characteristics of circumpulsar detectable precessing discs are estimated as a function of distance from the Solar system. Speculations on detection rates are presented.

  18. The formation of planets by disc fragmentation

    Directory of Open Access Journals (Sweden)

    Stamatellos Dimitris

    2013-04-01

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

  19. Lumbar disc cyst with contralateral radiculopathy

    Directory of Open Access Journals (Sweden)

    Kishore Tourani

    2012-08-01

    Full Text Available Disc cysts are uncommon intraspinal cystic lesions located in the ventrolateral epidural space. They communicate with the nucleus pulposus of the intervertebral disc and cause symptoms by radicular compression. We report a unique case of lumbar disc cyst that was associated with disc herniation and contralateral radiculopathy. A 22 year old male presented with one month history of back-ache radiating to the left leg. Magnetic Resonance Imaging (MRI showed L3-L4 disc herniation with annular tear and cystic lesion in the extradural space anterior to the thecal sac on right side, which increased in size over a period of 3 weeks. L3 laminectomy and bilateral discectomy and cyst excision was done with partial improvement of patients symptoms.

  20. Strongly magnetized accretion discs require poloidal flux

    Science.gov (United States)

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

    2016-08-01

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

  1. Strongly magnetized accretion discs require poloidal flux

    CERN Document Server

    Salvesen, Greg; Simon, Jacob B; Begelman, Mitchell C

    2016-01-01

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

  2. Magnetic resonance imaging of intervertebral disc degeneration

    Energy Technology Data Exchange (ETDEWEB)

    Maeda, Hiroshi; Noguchi, Masao (Kitakyushu City Yahata Hospital, Fukuoka (Japan)); Kira, Hideaki; Fujiki, Hiroshi; Shimokawa, Isao; Hinoue, Kaichi

    1993-02-01

    The aim of this study was to correlate the degree of lumbar intervertebral disc degeneration with findings of magnetic resonance imaging (MRI). Seventeen autopsied (from 7 patients) and 21 surgical (from 20 patients) intervertebral discs were used as specimens for histopathological examination. In addition, 21 intervertebral discs were examined on T2-weighted images. Histopathological findings from both autopsied and surgical specimens were well correlated with MRI findings. In particular, T2-weighted images reflected increased collagen fibers and rupture within the fibrous ring accurately. However, when severely degenerated intervertebral discs and hernia protruding the posterior longitudinal ligament existed, histological findings were not concordant well with T2-weighted images. Morphological appearances of autopsy specimens, divided into four on T2-weighted images, were well consistent with histological degeneration. This morphological classification, as shown on T2-weighted images, could also be used in the evaluation of intervertebral disc degeneration. (N.K.).

  3. Lumbar Epidural Varix Mimicking Disc Herniation.

    Science.gov (United States)

    Bursalı, Adem; Akyoldas, Goktug; Guvenal, Ahmet Burak; Yaman, Onur

    2016-07-01

    Lumbar radiculopathy is generally caused by such well-recognized entity as lumbar disc herniation in neurosurgical practice; however rare pathologies such as thrombosed epidural varix may mimic them by causing radicular symptoms. In this case report, we present a 26-year-old man with the complaint of back and right leg pain who was operated for right L4-5 disc herniation. The lesion interpreted as an extruded disc herniation preoperatively was found to be a thrombosed epidural varix compressing the nerve root preoperatively. The nerve root was decompressed by shrinking the lesion with bipolar thermocoagulation and excision. The patient's complaints disappeared in the postoperative period. Thrombosed lumbar epidural varices may mimic lumbar disc herniations both radiologically and clinically. Therefore, must be kept in mind in the differential diagnosis of lumbar disc herniations. Microsurgical techniques are mandatory for the treatment of these pathologies and decompression with thermocoagulation and excision is an efficient method.

  4. Angular momentum transport in protostellar discs

    CERN Document Server

    Salmeron, Roberto Aureliano; Wardle, M; Salmeron, Raquel; Konigl, Arieh; Wardle, Mark

    2006-01-01

    Angular momentum transport in protostellar discs can take place either radially, through turbulence induced by the magnetorotational instability (MRI), or vertically, through the torque exerted by a large-scale magnetic field that threads the disc. Using semi-analytic and numerical results, we construct a model of steady-state discs that includes vertical transport by a centrifugally driven wind as well as MRI-induced turbulence. We present approximate criteria for the occurrence of either one of these mechanisms in an ambipolar diffusion-dominated disc. We derive ``strong field'' solutions in which the angular momentum transport is purely vertical and ``weak field'' solutions that are the stratified-disc analogues of the previously studied MRI channel modes; the latter are transformed into accretion solutions with predominantly radial angular-momentum transport when we implement a turbulent-stress prescription based on published results of numerical simulations. We also analyze ``intermediate field strength'...

  5. Gravitoturbulence in magnetised protostellar discs

    CERN Document Server

    Riols, A

    2016-01-01

    Gravitational instability (GI) features in several aspects of protostellar disk 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 MHD simulations with an imposed toroidal field. In the regime of moderate plasma beta, we find that the system supports a hot gravito-turbulent state, characterised by considerable magnetic energy and stress and a surprisingly large Toomre parameter $Q~10$. This result has potential implications for disk structure, vertical thickness, ionisation, 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 disk. Though our focus is on...

  6. Lumbar herniated disc: spontaneous regression

    Science.gov (United States)

    Yüksel, Kasım Zafer

    2017-01-01

    Background Low back pain is a frequent condition that results in substantial disability and causes admission of patients to neurosurgery clinics. To evaluate and present the therapeutic outcomes in lumbar disc hernia (LDH) patients treated by means of a conservative approach, consisting of bed rest and medical therapy. Methods This retrospective cohort was carried out in the neurosurgery departments of hospitals in Kahramanmaraş city and 23 patients diagnosed with LDH at the levels of L3−L4, L4−L5 or L5−S1 were enrolled. Results The average age was 38.4 ± 8.0 and the chief complaint was low back pain and sciatica radiating to one or both lower extremities. Conservative treatment was administered. Neurological examination findings, durations of treatment and intervals until symptomatic recovery were recorded. Laségue tests and neurosensory examination revealed that mild neurological deficits existed in 16 of our patients. Previously, 5 patients had received physiotherapy and 7 patients had been on medical treatment. The number of patients with LDH at the level of L3−L4, L4−L5, and L5−S1 were 1, 13, and 9, respectively. All patients reported that they had benefit from medical treatment and bed rest, and radiologic improvement was observed simultaneously on MRI scans. The average duration until symptomatic recovery and/or regression of LDH symptoms was 13.6 ± 5.4 months (range: 5−22). Conclusions It should be kept in mind that lumbar disc hernias could regress with medical treatment and rest without surgery, and there should be an awareness that these patients could recover radiologically. This condition must be taken into account during decision making for surgical intervention in LDH patients devoid of indications for emergent surgery. PMID:28119770

  7. Generation of highly inclined protoplanetary discs through single stellar flybys

    CERN Document Server

    Xiang-Gruess, Meng

    2015-01-01

    We study the three-dimensional evolution of a viscous protoplanetary disc which is perturbed by a passing star on a parabolic orbit. The aim is to test whether a single stellar flyby is capable to excite significant disc inclinations which would favour the formation of so-called misaligned planets. We use smoothed particle hydrodynamics to study inclination, disc mass and angular momentum changes of the disc for passing stars with different masses. We explore different orbital configurations for the perturber's orbit to find the parameter spaces which allow significant disc inclination generation. Prograde inclined parabolic orbits are most destructive leading to significant disc mass and angular momentum loss. In the remaining disc, the final disc inclination is only below $20^\\circ$. This is due to the removal of disc particles which have experienced the strongest perturbing effects. Retrograde inclined parabolic orbits are less destructive and can generate disc inclinations up to $60^\\circ$. The final disc...

  8. Stellar irradiated discs and implications on migration of embedded planets II: accreting-discs

    CERN Document Server

    Bitsch, Bertram; Lega, Elena; Crida, Aurélien

    2014-01-01

    The strength and direction of migration of embedded low mass planets depends on the disc's structure. It has been shown that, in discs with viscous heating and radiative transport, the migration can be directed outwards. In this paper we investigate the influence of a constant dM/dt-flux through the disc, as well as the influence of the disc's metallicity on the disc's thermodynamics. We focus on dM/dt discs, which have a net mass flux through them. Utilizing the resulting disc structure, we determine the regions of outward migration in the disc. We perform numerical hydrosimulations of dM/dt discs with viscous heating, radiative cooling and stellar irradiation in 2D in the r-z-plane. We use 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 is studied by using torque formulae. For a disc of gas surfac...

  9. Autologous adipose stem cells and polylactide discs in the replacement of the rabbit temporomandibular joint disc

    Science.gov (United States)

    Ahtiainen, Katja; Mauno, Jari; Ellä, Ville; Hagström, Jaana; Lindqvist, Christian; Miettinen, Susanna; Ylikomi, Timo; Kellomäki, Minna; Seppänen, Riitta

    2013-01-01

    The temporomandibular joint (TMJ) disc lacks functional replacement after discectomy. We investigated tissue-engineered bilayer polylactide (PLA) discs and autologous adipose stem cells (ASCs) as a potential replacement for the TMJ disc. These ASC discs were pre-cultured either in control or in differentiation medium, including transforming growth factor (TGF)-β1 for one week. Prior to implantation, expression of fibrocartilaginous genes was measured by qRT-PCR. The control and differentiated ASC discs were implanted, respectively, in the right and left TMJs of rabbits for six (n = 5) and 12 months (n = 5). Thereafter, the excised TMJ areas were examined with cone beam computed tomography (CBCT) and histology. No signs of infection, inflammation or foreign body reactions were detected at histology, whereas chronic arthrosis and considerable condylar hypertrophy were observed in all operated joints at CBCT. The left condyle treated with the differentiated ASC discs appeared consistently smoother and more sclerotic than the right condyle. The ASC disc replacement resulted in dislocation and morphological changes in the rabbit TMJ. The ASC discs pre-treated with TGF-β1 enhanced the condylar integrity. While adverse tissue reactions were not shown, the authors suggest that with improved attachment and design, the PLA disc and biomaterial itself would hold potential for TMJ disc replacement. PMID:23720535

  10. The properties of discs around planets and brown dwarfs as evidence for disc fragmentation

    CERN Document Server

    Stamatellos, Dimitris

    2015-01-01

    Direct imaging searches have revealed many very low-mass objects, including a small number of planetary mass objects, as wide-orbit companions to young stars. The formation mechanism of these objects remains uncertain. In this paper we present the predictions of the disc fragmentation model regarding the properties of the discs around such low-mass objects. We find that the discs around objects that have formed by fragmentation in discs hosted by Sun-like stars (referred to as 'parent' discs and 'parent' stars) are more massive than expected from the ${M}_{\\rm disc}-M_*$ relation (which is derived for stars with masses $M_*>0.2 {\\rm M}_{\\odot}$). Accordingly, the accretion rates onto these objects are also higher than expected from the $\\dot{M}_*-M_*$ relation. Moreover there is no significant correlation between the mass of the brown dwarf or planet with the mass of its disc nor with the accretion rate from the disc onto it. The discs around objects that form by disc fragmentation have larger than expected m...

  11. Autologous adipose stem cells and polylactide discs in the replacement of the rabbit temporomandibular joint disc.

    Science.gov (United States)

    Ahtiainen, Katja; Mauno, Jari; Ellä, Ville; Hagström, Jaana; Lindqvist, Christian; Miettinen, Susanna; Ylikomi, Timo; Kellomäki, Minna; Seppänen, Riitta

    2013-08-06

    The temporomandibular joint (TMJ) disc lacks functional replacement after discectomy. We investigated tissue-engineered bilayer polylactide (PLA) discs and autologous adipose stem cells (ASCs) as a potential replacement for the TMJ disc. These ASC discs were pre-cultured either in control or in differentiation medium, including transforming growth factor (TGF)-β1 for one week. Prior to implantation, expression of fibrocartilaginous genes was measured by qRT-PCR. The control and differentiated ASC discs were implanted, respectively, in the right and left TMJs of rabbits for six (n = 5) and 12 months (n = 5). Thereafter, the excised TMJ areas were examined with cone beam computed tomography (CBCT) and histology. No signs of infection, inflammation or foreign body reactions were detected at histology, whereas chronic arthrosis and considerable condylar hypertrophy were observed in all operated joints at CBCT. The left condyle treated with the differentiated ASC discs appeared consistently smoother and more sclerotic than the right condyle. The ASC disc replacement resulted in dislocation and morphological changes in the rabbit TMJ. The ASC discs pre-treated with TGF-β1 enhanced the condylar integrity. While adverse tissue reactions were not shown, the authors suggest that with improved attachment and design, the PLA disc and biomaterial itself would hold potential for TMJ disc replacement.

  12. Minimizing cryopreservation-induced loss of disc cell activity for storage of whole intervertebral discs

    Directory of Open Access Journals (Sweden)

    SCW Chan

    2010-06-01

    Full Text Available Severe intervertebral disc (IVD degeneration often requires disc excision and spinal fusion, which leads to loss of spinal segment mobility. Implantation of an allograft disc or tissue engineered disc construct emerges as an alternative to artificial disc replacement for preserving the motion of the degenerated level. Establishment of a bank of cadaveric or engineered cryopreserved discs enables size matching, and facilitates clinical management. However, there is a lack of understanding of the behaviour of disc cells during cryopreservation, as well as how to maximize their survival, such that disc graft properties can be preserved. Here, we report on the effect of alterations in cooling rates, cryoprotective agents (CPAs, and duration of pre-cryopreservation incubation in CPA on cellular activity in whole porcine lumbar discs. Our results indicated that cooling rates of -0.3°C/min and -0.5°C /min resulted in the least loss of metabolic activity in nucleus pulposus (NP and annulus fibrosus (AF respectively, while metabolic activity is best maintained by using a combination of 10% dimethylsulphoxide (DMSO and 10% propylene-glycol (PG as CPA. By the use of such parameters, metabolic activity of the NP and the AF cells could be maintained at 70% and 45%, respectively, of that of the fresh tissue. Mechanical testing and histological evaluation showed no significant differences in mechanical properties or alterations in disc structure compared to fresh discs. Despite the limitations of the animal model, our findings provide a framework for establishing an applicable cryopreservation protocol for human disc allografts or tissue-engineered disc constructs.

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

    Science.gov (United States)

    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.

  14. Structure of radiation dominated gravitoturbulent quasar discs

    CERN Document Server

    Shadmehri, Mohsen; Dib, Sami

    2016-01-01

    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 like 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....

  15. Chemical separation of disc components using RAVE

    CERN Document Server

    Wojno, Jennifer; Steinmetz, Matthias; McMillan, Paul J; Matijevič, Gal; Binney, James; Wyse, Rosemary F G; Boeche, Corrado; Just, Andreas; Grebel, Eva K; Siebert, Arnaud; Bienaymé, Olivier; Gibson, Brad K; Zwitter, Tomaž; Bland-Hawthorn, Joss; Navarro, Julio F; Parker, Quentin A; Reid, Warren; Seabroke, George; Watson, Fred

    2016-01-01

    We present evidence from the RAdial Velocity Experiment (RAVE) survey of chemically separated, kinematically distinct disc components in the solar neighbourhood. We apply probabilistic chemical selection criteria to separate our sample into $\\alpha$-low (`thin disc') and $\\alpha$-high (`thick disc') components. Using newly derived distances, which will be utilized in the upcoming RAVE DR5, we explore the kinematic trends as a function of metallicity for each of the disc components. For our thin disc stars, we find a negative trend in the mean rotational velocity ($V_{\\mathrm{\\phi}}$) as a function of iron abundance ([Fe/H]). We measure a positive trend in $\\partial V_{\\mathrm{\\phi}}$/$\\partial$[Fe/H] for the thick disc, consistent with results from high-resolution surveys. We also find differences between the chemical thin and thick discs in all three components of velocity dispersion. We discuss the implications of an $\\alpha$-low, metal-rich population originating from the inner Galaxy, where the orbits of ...

  16. Have proto-planetary discs formed planets?

    CERN Document Server

    Greaves, J S

    2010-01-01

    It has recently been noted that many discs around T Tauri stars appear to comprise only a few Jupiter-masses of gas and dust. Using millimetre surveys of discs within six local star-formation regions, we confirm this result, and find that only a few percent of young stars have enough circumstellar material to build gas giant planets, in standard core accretion models. Since the frequency of observed exo-planets is greater than this, there is a `missing mass' problem. As alternatives to simply adjusting the conversion of dust-flux to disc mass, we investigate three other classes of solution. Migration of planets could hypothetically sweep up the disc mass reservoir more efficiently, but trends in multi-planet systems do not support such a model, and theoretical models suggest that the gas accretion timescale is too short for migration to sweep the disc. Enhanced inner-disc mass reservoirs are possible, agreeing with predictions of disc evolution through self-gravity, but not adding to millimetre dust-flux as t...

  17. Stem cells sources for intervertebral disc regeneration

    Institute of Scientific and Technical Information of China (English)

    Gianluca; Vadalà; Fabrizio; Russo; Luca; Ambrosio; Mattia; Loppini; Vincenzo; Denaro

    2016-01-01

    Intervertebral disc regeneration field is rapidly growing since disc disorders represent a major health problem in industrialized countries with very few possible treatments.Indeed, current available therapies are symptomatic, and surgical procedures consist in disc removal and spinal fusion, which is not immune to regardable concerns about possible comorbidities, cost-effectiveness, secondary risks and long-lasting outcomes. This review paper aims to share recent advances in stem cell therapy for the treatment of intervertebral disc degeneration. In literature the potential use of different adult stem cells for intervertebral disc regeneration has already been reported. Bone marrow mesenchymal stromal/stem cells, adipose tissue derived stem cells, synovial stem cells, muscle-derived stem cells, olfactory neural stem cells, induced pluripotent stem cells, hematopoietic stem cells, disc stem cells, and embryonic stem cells have been studied for this purpose either in vitro or in vivo. Moreover, several engineered carriers(e.g., hydrogels), characterized by full biocompatibility and prompt biodegradation, have been designed and combined with different stem cell types in order to optimize the local and controlled delivery of cellular substrates in situ. The paper overviews the literature discussing the current status of our knowledge of the different stem cells types used as a cell-based therapy for disc regeneration.

  18. Optically-thick accretion discs with advection

    Institute of Scientific and Technical Information of China (English)

    陈林红; 吴枚; 尚仁成

    2002-01-01

    The structures of optically-thick accretion discs with radial advection have been investigated by the iteration and integration algorithms. The advective cooling term changes mostly the inner part of disc solution, and even results in an optically-thick advection-dominated accretion flow (ADAF). Three distinct branches-the outer Shakura-Sunyaev disc (SSD), the inner ADAF and the middle transition layer-are found for a super-Eddington disc. The SSD-ADAF transition radius can be estimated as 18(M/ME)RG where RG is the Schwarzschild radius, M is the mass accretion rate and ME is the Eddington accretion rate. SSD solutions calculated with the iteration and integration methods are identical, while ADAF solutions obtained by these two methods differ greatly. Detailed algorithms and their differences have been analysed. The iteration algorithm is not self-consistent, since it implies that the dimensionless advection factor ξ is invariant, but in the inner ADAF region the variation of ξ is not negligible. The integration algorithm is always effective for the whole region of an optically-thick disc if the accretion rate is no smaller than 10-4ME. For optically-thin discs, the validity of these two algorithms is different. We suggest that the integration method be employed to calculate the global solution of a disc model without assuming ξ to be a constant. We also discuss its application to the emergent continuum spectrum in order to explain observational facts.

  19. The tidal disruption of protoplanetary accretion discs

    CERN Document Server

    Larwood, J D

    1997-01-01

    In this paper we revisit the problem of the tidal interaction occuring between a protostellar accretion disc and a secondary point mass following a parabolic trajectory. We model the disc response analytically and we compare our results with three-dimensional SPH simulations. Inviscid as well as viscous hydrodynamics is considered. We show that in a viscous system the response derived from inviscid considerations is predominant even for the highest estimates of an anomalous disc shear viscosity. The angular momentum lost from the disc during the encounter is derived from linear theory, for distant fly-bys, as well as the changes to the disc orientation expected in non-coplanar encounters. It is shown that the target discs can become warped and precess by a small amount during non-coplanar encounters. This small precession is shown to give rise to a relative tilt of the disc which is always more important for determining its final orientation than is the change to the orbital inclination. We discuss the implic...

  20. Intradiscal pressure measurements in normal discs, compressed discs and compressed discs treated with axial posterior disc distraction: an experimental study on the rabbit lumbar spine model.

    Science.gov (United States)

    Guehring, Thorsten; Unglaub, Frank; Lorenz, Helga; Omlor, Georg; Wilke, Hans-Joachim; Kroeber, Markus W

    2006-05-01

    Intervertebral disc (IVD) pressure measurement is an appropriate method for characterizing spinal loading conditions. However, there is no human or animal model that provides sufficient IVD pressure data. The aim of our study was to establish physiological pressure values in the rabbit lumbar spine and to determine whether temporary external disc compression and distraction were associated with pressure changes. Measurements were done using a microstructure-based fibreoptic sensor. Data were collected in five control rabbits (N, measurement lying prone at segment L3/4 at day 28), five rabbits with 28 days of axial compression (C, measurement at day 28) and three rabbits with 28 days of axial compression and following 28 days of axial distraction (D, measurement at day 56). Disc compression and distraction was verified by disc height in lateral radiographs. The controls (N) showed a level-related range between 0.25 MPa-0.45 MPa. The IVD pressure was highest at level L3/4 (0.42 MPa; range 0.38-0.45) with a decrease in both cranial and caudal adjacent segments. The result for C was a significant decrease in IVD pressure (0.31 MPa) when compared with controls (P=0.009). D showed slightly higher median IVD pressure (0.32 MPa) compared to C, but significantly lower levels when compared with N (P=0.037). Our results indicate a high range of physiological IVD pressure at different levels of the lumbar rabbit spine. Temporary disc compression reduces pressure when compared with controls. These data support the hypothesis that temporary external compression leads to moderate disc degeneration as a result of degradation of water-binding disc matrix or affected active pumping mechanisms of nutrients into the disc. A stabilization of IVD pressure in discs treated with temporary distraction was observed.

  1. Endoscopic anterior decompression in cervical disc disease

    Directory of Open Access Journals (Sweden)

    Yad Ram Yadav

    2014-01-01

    Full Text Available Background: Although microscopic anterior cervical discectomy with or without fusion are common surgical procedures for treatment of cervical herniated discs, loss of disc height, pseudarthrosis, and adjacent disc degeneration are some of the problems associated with it. This study is aimed to evaluate results of endoscopic microforaminotomy in cervical disc diseases. Materials and Methods: A prospective study of 50 patients of mono segmental soft or hard disc causing myeloradiculopathy was undertaken. A visual analogue scale (VAS for neck and arm pain and functional outcomes using the Nurick grading system were assessed. There were 28, 12, 8, and 2 patients at C5-6, C6-7, C4-5, and C3-4 levels disc diseases, respectively. Patients with two or more level disc, instabilities, disc extending more than half vertebral body height, and previous operation at the same segment were excluded. Results: Age ranged from 21 to 67 years. Average postoperative reduction in disc height, operating time, and blood loss was 1.1 mm, 110 minutes, and 30 ml, respectively. Average pre-operative VAS score for arm pain and Nurick grading was 7.6 and 2.7, which improved to 1.9 and 0.82, respectively. All patients improved; 1, 2, 3 grade improvement was seen in 10, 27, and 10 patients, respectively. There was no significant complication or any mortality. Conclusion: Although longer follow up of large number of patients is required, endoscopic microforaminotomy is a safe and an effective alternative to microscopic anterior discectomy with or without fusion.

  2. Spectroscopic Parameters of Lumbar Intervertebral Disc Material

    Science.gov (United States)

    Terbetas, G.; Kozlovskaja, A.; Varanius, D.; Graziene, V.; Vaitkus, J.; Vaitkuviene, A.

    2009-06-01

    There are numerous methods of investigating intervertebral disc. Visualization methods are widely used in clinical practice. Histological, imunohistochemical and biochemical methods are more used in scientific research. We propose that a new spectroscopic investigation would be useful in determining intervertebral disc material, especially when no histological specimens are available. Purpose: to determine spectroscopic parameters of intervertebral disc material; to determine emission spectra common for all intervertebral discs; to create a background for further spectroscopic investigation where no histological specimen will be available. Material and Methods: 20 patients, 68 frozen sections of 20 μm thickness from operatively removed intervertebral disc hernia were excited by Nd:YAG microlaser STA-01-TH third harmonic 355 nm light throw 0, 1 mm fiber. Spectrophotometer OceanOptics USB2000 was used for spectra collection. Mathematical analysis of spectra was performed by ORIGIN multiple Gaussian peaks analysis. Results: In each specimen of disc hernia were found distinct maximal spectral peaks of 4 types supporting the histological evaluation of mixture content of the hernia. Fluorescence in the spectral regions 370-700 nm was detected in the disc hernias. The main spectral component was at 494 nm and the contribution of the components with the peak wavelength values at 388 nm, 412 nm and 435±5 nm were varying in the different groups of samples. In comparison to average spectrum of all cases, there are 4 groups of different spectral signatures in the region 400-500 nm in the patient groups, supporting a clinical data on different clinical features of the patients. Discussion and Conclusion: besides the classical open discectomy, new minimally invasive techniques of treating intervertebral disc emerge (PLDD). Intervertebral disc in these techniques is assessed by needle, no histological specimen is taken. Spectroscopic investigation via fiber optics through the

  3. Groups, cacti and framed little discs

    CERN Document Server

    Hepworth, Richard

    2010-01-01

    Let G be a topological group. Then the based loopspace of G is an algebra over the cacti operad, while the double loopspace of the classifying space of G is an algebra over the framed little discs operad. This paper shows that these two algebras are equivalent, in the sense that they are weakly equivalent E-algebras, where E is an operad weakly equivalent to both framed little discs and cacti. We recover the equivalence between cacti and framed little discs, and Menichi's isomorphism between the BV-algebras obtained by taking the homology of the loopspace of G and of the double loopspace of BG.

  4. Modeling and Thermal Analysis of Disc

    OpenAIRE

    Brake Praveena S; Lava Kumar M

    2014-01-01

    The disc brake is a device used for slowing or stopping the rotation of the vehicle. Number of times using the brake for vehicle leads to heat generation during braking event, such that disc brake undergoes breakage due to high Temperature. Disc brake model is done by CATIA and analysis is done by using ANSYS workbench. The main purpose of this project is to study the Thermal analysis of the Materials for the Aluminum, Grey Cast Iron, HSS M42, and HSS M2. A comparison between ...

  5. A lumbar disc surgery predictive score card.

    Science.gov (United States)

    Finneson, B E

    1978-06-01

    A lumbar disc surgery predictive score card or questionnaire has been developed to assess potential candidates for excision of a herniated lumbar disc who have not previously undergone lumbar spine surgery. It is not designed to encompass patients who are being considered for other types of lumbar spine surgery, such as decompressive laminectomy or fusion. In an effort to make the "score card" usable by almost all physicians who are involved in lumbar disc surgery, only studies which have broad acceptance and are generally employed are included. Studies which have less widespread use such as electromyogram, discogram, venogram, special psychologic studies (MMPI, pain drawings) have been purposely excluded.

  6. Stellar irradiated discs and implications on migration of embedded planets I: equilibrium discs

    CERN Document Server

    Bitsch, Bertram; Morbidelli, Alessandro; Kley, Willy; Dobbs-Dixon, Ian

    2012-01-01

    The strength and direction of migration of low mass planets depends on the disc's thermodynamics. 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. We investigate the influence of opacity and stellar irradiation on the disc thermodynamics. Utilizing the resulting disc structure, we determine the regions of outward migration. We perform two-dimensional numerical simulations of equilibrium discs with viscous heating, radiative cooling and stellar irradiation. We use the 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 is studied by using torque formulae. In the constant opacity case, we reproduce the analytical results of a black-body disc: the stellar irradiation dominates in the outer regions -- leading to flaring -...

  7. Investigation of the coatings applied onto brake discs on disc-brake pad pair

    Directory of Open Access Journals (Sweden)

    I. Kiliçaslan

    2009-07-01

    Full Text Available While braking, according to the severity of it, thermal, metallurgical, constructive and tribological occurrences emerge on the brake disc-pad interface. In this study, NiCr was sprayed as bonding layer onto the discs, one ofwhich was coated with Al2O3-TiO2 by plasma spray and the other was coated with NiCr-Cr3C2 by High Velocity Oxygen Fuel (HVOF. In addition, the discs were tested with inertia dynamometer according to SAE’s J2522 testing procedure. The measurements showed that although the pads of the coated discs were exposed to higher braking temperatures, friction coefficient of the disc coated with NiCr- Cr3C2 was obtained 6 % higher compared to the original disc.

  8. Burned-out discs stop hurting: fact or fiction?

    DEFF Research Database (Denmark)

    Bendix, Tom; Kjaer, Per; Korsholm, Lars

    2008-01-01

    ). The risk for LBP during the past year attributed to black discs was 11%. CONCLUSION: The data could not support the hypothesis that severely degenerated discs are "burned out" and become less painful. People with black discs had a higher prevalence of LBP compared to those with grey or normal discs...

  9. Cervical disc arthroplasty with ProDisc-C artificial disc: 5-year radiographic follow-up results

    Institute of Scientific and Technical Information of China (English)

    ZHAO Yan-bin; SUN Yu; ZHOU Fei-fei; LIU ZHONG-jun

    2013-01-01

    Background Cervical disc arthroplasty is an alternative surgery to standard cervical decompression and fusion for disc degeneration.Different types of cervical disc prosthesis are used in China.The aim of this study was to evaluate the radiographic outcomes of cervical arthroplasty using the ProDisc-C prosthesis.Methods Radiographic evaluation,including static and dynamic flexion-extension lateral images,was performed at baseline and at final follow-up.Results Twenty six patients who had single-level ProDisc-C arthroplasty were followed up for a mean period of 63 months (56-76 months).The range of motion at the operated level was 9.3°±3.7° at baseline and 7.3°±3.5° at final follow-up,with a significant difference (P <0.05).Seventeen of 26 levels (65.4%) developed heterotopic ossification:three were classified as grade Ⅱ,13 were classified as grade Ⅲ,and 1 as grade Ⅳ,according to McAfee's classification.Forty nine adjacent segments were evaluated by lateral Ⅹ-ray and 18 (36.7%) segments developed adjacent segment degenerations.Conclusions ProDisc-C arthroplasty had acceptable radiographic results at 5-year follow-up.The range of motion was preserved.However,more than 60% of the patients developed heterotopic ossification.

  10. Medium-term outcomes of artificial disc replacement for severe cervical disc narrowing

    Institute of Scientific and Technical Information of China (English)

    Chao-Hung Yeh; Che-Wei Hung; Cheng-Hsing Kao; Chien-Ming Chao

    2014-01-01

    Objective:To determine if theBryan cervical disc prosthesis could relieve objective neurological symptoms, signs, and restore mobility in patients with severe cervical disc narrowing. Methods:Clinical data of thirty-two patients underwentBryan cervical disc replacement has been collected fromApril2006 toFebruary2010.Severe cervical disc narrowing with gradeV disc degeneration were included in this study.Bryan cervical disc prostheses have been implanted through anterior approach.JapaneseOrthopedicsAssociation(JOA) score, visual analog scale, Odom’s scale, and flexion-extension radiological follow-ups were applied for evaluations. Results:A total of41Bryan disc prostheses from32 patients with an average follow-up duration of33.5 months(range23 to44 months) were evaluated.Clinical functions of patients were significantly improved.Preoperative averaged visual analog scale score of6.3±2.2 was decreased to1.3±1.2(at36 months,P<0.001), while preoperative averagedJOA score of14.4±1.2 was increased to16.3±0.9(at36 months,P<0.001).Thirty of32 patients received excellent to good outcomes inOdom’s scale.Averaged mobility was restored to(9.9±3.2)°at the last follow-up evaluation of36 months.No subsidence or migration of implant was identified. Conclusions:Acceptable clinical outcome for treatment of severe cervical disc narrowing with cervical disc replacement technique has been performed in current study.Most patients maintained good postoperative mobility and no significant adjacent level degeneration were found.Cervical disc replacement may be applicable in treatment of severe cervical disc narrowing; however, longer follow-ups are required for ensuring the long-term efficacy of cervical disc replacement.

  11. Axial T2* mapping in intervertebral discs: a new technique for assessment of intervertebral disc degeneration

    Energy Technology Data Exchange (ETDEWEB)

    Hoppe, Sven; Quirbach, Sebastian; Krause, Fabian G.; Benneker, Lorin M. [Inselspital, Berne University Hospital, Department of Orthopaedic Surgery, Berne (Switzerland); Mamisch, Tallal C. [Inselspital, Berne University Hospital, Department of Radiology, Berne (Switzerland); Werlen, Stefan [Clinic Sonnenhof, Department of Radiology, Berne (Switzerland)

    2012-09-15

    To demonstrate the potential benefits of biochemical axial T2* mapping of intervertebral discs (IVDs) regarding the detection and grading of early stages of degenerative disc disease using 1.5-Tesla magnetic resonance imaging (MRI) in a clinical setting. Ninety-three patients suffering from lumbar spine problems were examined using standard MRI protocols including an axial T2* mapping protocol. All discs were classified morphologically and grouped as ''healthy'' or ''abnormal''. Differences between groups were analysed regarding to the specific T2* pattern at different regions of interest (ROIs). Healthy intervertebral discs revealed a distinct cross-sectional T2* value profile: T2* values were significantly lower in the annulus fibrosus compared with the nucleus pulposus (P = 0.01). In abnormal IVDs, T2* values were significantly lower, especially towards the centre of the disc representing the expected decreased water content of the nucleus (P = 0.01). In herniated discs, ROIs within the nucleus pulposus and ROIs covering the annulus fibrosus showed decreased T2* values. Axial T2* mapping is effective to detect early stages of degenerative disc disease. There is a potential benefit of axial T2* mapping as a diagnostic tool, allowing the quantitative assessment of intervertebral disc degeneration. circle Axial T2* mapping effective in detecting early degenerative disc disease. (orig.)

  12. Treatment of lumbar disc herniation by percutaneous laser disc decompression (PLDD) and modified PLDD

    Science.gov (United States)

    Chi, Xiao fei; Li, Hong zhi; Wu, Ru zhou; Sui, Yun xian

    2005-07-01

    Objective: To study the micro-invasive operative method and to compare the effect of treatment of PLDD and modified PLDD for Lumbar Disc Herniation. Method: Vaporized part of the nucleus pulposus in single or multiple point after acupuncture into lumbar disc, to reach the purpose of the decompression of the lumbar disc. Result: Among the 19 cases of the regular PLDD group, the excellent and good rate was 63.2%, and among the 40 cases of the modified PLDD group, the excellent and good rate was 82.5%. Conclusion: The modified PLDD has good effect on the treatment for lumbar disc herniation.

  13. Transradicular lumbar disc herniation: An extreme variant of intraradicular disc herniation.

    Science.gov (United States)

    Kasliwal, Manish K; Shimer, Adam L

    2015-01-01

    Intradural or intraradicular lumbar disc herniation (IDH) is a relatively rare condition often diagnosed intraoperatively. We encountered an extreme variant of IDH - a transradicular herniation as the disc material extruded through the lumbar nerve root through a split essentially transecting the nerve root. While failure to recognize intradural and intraradicular disc herniation can lead to failed back surgery, the variant described in the present case could lead to iatrogenic injury and complication if not recognized. A unique case of transradicular lumbar disc herniation in a 25-year-old patient is presented with the depiction of intraoperative images supplementing the text.

  14. CFD Analysis Of Straight Ventilated Disc Brake

    Directory of Open Access Journals (Sweden)

    Nikhil K

    2016-05-01

    Full Text Available Brakes are the key pieces of a vehicle that plays an active role in safety and performance of the system. The study of aerodynamic cooling of a disc brake in real working condition of vehicle is important in present situations. Brake discs get very hot quickly, so it should be dissipated properly through different modes of heat transfer. Contributions of these heat transfer modes are different in different type of problems. The cooling transfer rates are different in vane surface and frictional surface of a disc brake. Also the temperature varies in each small interval of braking time. So a transient problem simulation is important to study the cooling of a disc brake when a vehicle decelerates from a particular speed. ANSYS CFX tool is used for the simulation of this transient problem.

  15. Modeling and Thermal Analysis of Disc

    Directory of Open Access Journals (Sweden)

    Brake Praveena S

    2014-10-01

    Full Text Available The disc brake is a device used for slowing or stopping the rotation of the vehicle. Number of times using the brake for vehicle leads to heat generation during braking event, such that disc brake undergoes breakage due to high Temperature. Disc brake model is done by CATIA and analysis is done by using ANSYS workbench. The main purpose of this project is to study the Thermal analysis of the Materials for the Aluminum, Grey Cast Iron, HSS M42, and HSS M2. A comparison between the four materials for the Thermal values and material properties obtained from the Thermal analysis low thermal gradient material is preferred. Hence best suitable design, low thermal gradient material Grey cast iron is preferred for the Disc Brakes for better performance.

  16. Magnetic Field Amplification via Protostellar Disc Dynamos

    CERN Document Server

    Dyda, Sergei; Ustyugova, Galina V; Koldoba, Alexander V; Wasserman, Ira

    2015-01-01

    We model the generation of a magnetic field in a protostellar disc using an \\alpha-dynamo and perform axisymmetric magnetohydrodynamics (MHD) simulations of a T Tauri star. We find that for small values of the dimensionless dynamo parameter $\\alpha_d$ the poloidal field grows exponentially at a rate ${\\sigma} \\propto {\\Omega}_K \\sqrt{\\alpha_d}$ , before saturating to a value $\\propto \\sqrt{\\alpha_d}$ . The dynamo excites dipole and octupole modes, but quadrupole modes are suppressed, because of the symmetries of the seed field. Initial seed fields too weak to launch MHD outflows are found to grow sufficiently to launch winds with observationally relevant mass fluxes of order $10^{-9} M_{\\odot}/\\rm{yr}$ for T Tauri stars. For large values of $\\alpha_d$ magnetic loops are generated over the entire disc. These quickly come to dominate the disc dynamics and cause the disc to break up due to the magnetic pressure.

  17. Thermal analysis on motorcycle disc brake geometry

    Science.gov (United States)

    W. M. Zurin W., S.; Talib, R. J.; Ismail, N. I.

    2017-08-01

    Braking is a phase of slowing and stop the movement of motorcycle. During braking, the frictional heat was generated and the energy was ideally should be faster dissipated to surrounding to prevent the built up of the excessive temperature which may lead to brake fluid vaporization, thermoelastic deformation at the contact surface, material degradation and failure. In this paper, solid and ventilated type of motorcycle disc brake are being analyse using Computational Fluid Dynamic (CFD) software. The main focus of the analysis is the thermal behaviour during braking for solid and ventilated disc brake. A comparison between both geometries is being discussed to determine the better braking performance in term of temperature distribution. It is found that ventilated disc brake is having better braking performance in terms of heat transfer compare to solid disc.

  18. Stellar Wind Erosion of Protoplanetary Discs

    CERN Document Server

    Schnepf, Neesha R; Romanova, Marina

    2014-01-01

    An analytic model is developed for the erosion of protoplanetary gas discs by high velocity magnetized stellar winds. The winds are centrifugally driven from the surface of rapidly rotating, strongly magnetized young stars. The presence of the magnetic field in the wind leads to Reynolds numbers sufficiently large to cause a strongly turbulent wind/disk boundary layer which entrains and carries away the disc gas. The model uses the conservation of mass and momentum in the turbulent boundary layer. The time-scale for significant erosion depends on the disc accretion speed, accretion rate and on the wind mass loss rate. The time-scale is estimated to be ~2E6 yr. The stellar wind erosion may act in conjunction with photo-evaporation of the discs.

  19. Spiral shocks and accretion in discs

    Energy Technology Data Exchange (ETDEWEB)

    Spruit, H.C.; Matsuda, T.; Inoue, M.; Sawada, K.

    1987-12-01

    Recent numerical and analytical results on disc-like accretion with shock waves as the only dissipation mechanism are compared. The global properties of the process are similar to those of the viscous (..cap alpha..) disc model, but precise values of the effective ..cap alpha.. value as a function of the accretion rate can be calculated. At low values of the ratio of specific heats (..gamma.. < 1.45) accretion is possible without radiative losses. Such adiabatic accretion can occur in practice at high accretion rates on to low mass objects and may be important in the formation of planets. Following previous authors, it is pointed out that non-axisymmetric perturbations in the outer parts of a disc increase in amplitude as they propagate in and cause spiral shocks more easily in a disc than perturbations originating in the inner parts.

  20. Eclipse Mapping: Astrotomography of Accretion Discs

    CERN Document Server

    Baptista, Raymundo

    2015-01-01

    The Eclipse Mapping Method is an indirect imaging technique that transforms the shape of the eclipse light curve into a map of the surface brightness distribution of the occulted regions. Three decades of application of this technique to the investigation of the structure, the spectrum and the time evolution of accretion discs around white dwarfs in cataclysmic variables have enriched our understanding of these accretion devices with a wealth of details such as (but not limited to) moving heating/cooling waves during outbursts in dwarf novae, tidally-induced spiral shocks of emitting gas with sub-Keplerian velocities, elliptical precessing discs associated to superhumps, and measurements of the radial run of the disc viscosity through the mapping of the disc flickering sources. This chapter reviews the principles of the method, discusses its performance, limitations, useful error propagation procedures, as well as highlights a selection of applications aimed at showing the possible scientific problems that ha...

  1. [Disc electrophoresis of collagen protein (author's transl)].

    Science.gov (United States)

    Reitmayr, P; Verzár, F

    1975-01-01

    The composition of proteins extracted from tendon collagen is investigated by disc electrophoresis. No qualitative differences can be demonstrated between young and old collagen. The action of formaldehyde and methionine on the tendons has no effect on the electrophoretic picture.

  2. Clumps and Axisymmetric Features in Debris Discs

    CERN Document Server

    Jiang, Ing-Guey

    2013-01-01

    This paper studied the structures of debris discs, focusing on the conditions that can form an axisymmetric-looking outer disc from systems with inner clumps. The main conclusion was that as long as the dominated dust grains are smaller than the blowout size, it is easy to form an axisymmetric-looking outer debris disc, which is part of a quasi-steady state of the whole system. This quasi-steady state is established through the balance between grain generations and a continuous out-going grain flow. Assuming there is an event that starts planetesimal collisions and the corresponding grain generations, this balance can be approached in a few thousand years. This result suggested that a quasi-steady-state picture could solve the possible mass budget problem of Vega's outer debris disc.

  3. Massive thin accretion discs. Pt. 2; Polarization

    Energy Technology Data Exchange (ETDEWEB)

    Laor, A.; Netzer, H. (Tel Aviv Univ. (Israel)); Piran, T. (Hebrew Univ., Jerusalem (Israel). Racah Inst. of Physics)

    1990-02-15

    Thin accretion discs around massive black holes are believed to produce much of the observed optical-UV emission from AGN. Classical calculations predict that this radiation is highly polarized at large inclination angles, in contrast to observations of quasars and Seyfert galaxies. We have calculated the spectrum and polarization of such discs using an improved radiative transfer method with all the relevant opacity sources, and a full general relativistic treatment of the radiation propagation. (author).

  4. Lyman edges in AGN accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Czerny, B. (Copernicus Astronomical Center, Warsaw (Poland)); Pojmanski, G. (Warsaw Univ. (Poland). Obserwatorium Astronomiczne)

    1990-07-01

    We show that the basic difference in the two principal approaches to predictions of the Lyman edge in an accretion disc lies in the implicit assumption about the density of the radiating gas. Independent from the details, models predict a broad range of the edge sizes, both in absorption and in emission. Observed spectra do not exhibit any strong feature at 912 A but may still be consistent with an accretion disc mechanism if more advanced theory is developed. (author).

  5. The Annulus Property of Simple Holomorphic Discs

    CERN Document Server

    Zehmisch, Kai

    2010-01-01

    We show that any simple holomorphic disc admits the annulus property, i.e., each interior point is surrounded by an arbitrary small annulus consisting entirely of injective points. As an application we show that interior singularities of holomorphic discs can be resolved after slight perturbation of the involved almost complex structure. Moreover, for boundary points the analogue notion, the half-annulus property, is introduced and studied in detail.

  6. The annulus property of simple holomorphic discs

    OpenAIRE

    Zehmisch, Kai

    2013-01-01

    We show that any simple holomorphic disc admits the annulus property, i.e., each interior point is surrounded by an arbitrary small annulus consisting entirely of injective points. As an application we show that interior singularities of holomorphic discs can be resolved after slight perturbation of the almost complex structure. Moreover, for boundary points the analogue notion, the half-annulus property, is introduced and studied in detail.

  7. Gene expression profile analysis of human intervertebral disc degeneration

    OpenAIRE

    Kai Chen; Dajiang Wu; Xiaodong Zhu; Haijian Ni; Xianzhao Wei; Ningfang Mao; Yang Xie; Yunfei Niu; Ming Li

    2013-01-01

    In this study, we used microarray analysis to investigate the biogenesis and progression of intervertebral disc degeneration. The gene expression profiles of 37 disc tissue samples obtained from patients with herniated discs and degenerative disc disease collected by the National Cancer Institute Cooperative Tissue Network were analyzed. Differentially expressed genes between more and less degenerated discs were identified by significant analysis of microarray. A total of 555 genes were signi...

  8. Clumpy Disc and Bulge Formation

    CERN Document Server

    Perez, J; Tissera, P; Michel-Dansac, L

    2013-01-01

    We present a set of hydrodynamical/Nbody controlled simulations of isolated gas rich galaxies that self-consistently include 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 timescales 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 Sersic index, n > 2. Our physically-motivated Supernova feedback has a mild influence on clump survival and evolution, partially limiting the mass growth of clumps as the energy released per Supernova 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 ...

  9. Radio Monitoring of Protoplanetary Discs

    Science.gov (United States)

    Ubach, C.; Maddison, S. T.; Wright, C. M.; Wilner, D. J.; Lommen, D. J. P.; Koribalski, B.

    2017-01-01

    Protoplanetary disc systems observed at radio wavelengths often show excess emission above that expected from a simple extrapolation of thermal dust emission observed at short millimetre wavelengths. Monitoring the emission at radio wavelengths can be used to help disentangle the physical mechanisms responsible for this excess, including free-free emission from a wind or jet, and chromospheric emission associated with stellar activity. We present new results from a radio monitoring survey conducted with Australia Telescope Compact Array over the course of several years with observation intervals spanning days, months and years, where the flux variability of 11 T Tauri stars in the Chamaeleon and Lupus star forming regions was measured at 7 and 15 mm and 3 and 6 cm. Results show that for most sources are variable to some degree at 7 mm, indicating the presence of emission mechanisms other than thermal dust in some sources. Additionally, evidence of grain growth to cm-sized pebbles was found for some sources that also have signs of variable flux at 7 mm. We conclude that multiple processes contributing to the emission are common in T Tauri stars at 7 mm and beyond, and that a detection at a single epoch at radio wavelengths should not be used to determine all processes contributing to the emission.

  10. The maximum rotation of a galactic disc

    CERN Document Server

    Bottema, R

    1997-01-01

    The observed stellar velocity dispersions of galactic discs show that the maximum rotation of a disc is on average 63% of the observed maximum rotation. This criterion can, however, not be applied to small or low surface brightness (LSB) galaxies because such systems show, in general, a continuously rising rotation curve until the outermost measured radial position. That is why a general relation has been derived, giving the maximum rotation for a disc depending on the luminosity, surface brightness, and colour of the disc. As a physical basis of this relation serves an adopted fixed mass-to-light ratio as a function of colour. That functionality is consistent with results from population synthesis models and its absolute value is determined from the observed stellar velocity dispersions. The derived maximum disc rotation is compared with a number of observed maximum rotations, clearly demonstrating the need for appreciable amounts of dark matter in the disc region and even more so for LSB galaxies. Matters h...

  11. Magnetic white dwarfs with debris discs

    CERN Document Server

    Külebi, Baybars; Lorén-Aguilar, Pablo; Isern, Jordi; García-Berro, Enrique

    2013-01-01

    It has long been accepted that a possible mechanism for explaining the existence of magnetic white dwarfs is the merger of a binary white dwarf system, as there are viable mechanisms for producing sustainable magnetic fields within the merger product. However, the lack of rapid rotators in the magnetic white dwarf population has been always considered a problematic issue of this scenario. Smoothed Particle Hydrodynamics simulations show that in mergers in which the two white dwarfs have different masses a disc around the central compact object is formed. If the central object is magnetized it can interact with the disc through its magnetosphere. The torque applied by the disc changes the spin of the star, whereas the transferred angular momentum from the star to the disc determines the properties of the disc. In this work we build a model for the disc evolution under the effect of magnetic accretion, and for the angular momentum evolution of the star, which can be compared with the observations. Our model pre...

  12. Turbulent drag reduction through oscillating discs

    CERN Document Server

    Wise, Daniel J

    2014-01-01

    The changes of a turbulent channel flow subjected to oscillations of wall flush-mounted rigid discs are studied by means of direct numerical simulations. The Reynolds number is $R_\\tau$=$180$, based on the friction velocity of the stationary-wall case and the half channel height. The primary effect of the wall forcing is the sustained reduction of wall-shear stress, which reaches a maximum of 20%. A parametric study on the disc diameter, maximum tip velocity, and oscillation period is presented, with the aim to identify the optimal parameters which guarantee maximum drag reduction and maximum net energy saving, computed by taking into account the power spent to actuate the discs. This may be positive and reaches 6%. The Rosenblat viscous pump flow is used to predict the power spent for disc motion in the turbulent channel flow and to estimate localized and transient regions over the disc surface subjected to the turbulent regenerative braking effect, for which the wall turbulence exerts work on the discs. The...

  13. The Diversity of Thick Galactic Discs

    CERN Document Server

    Kasparova, Anastasia V; Chilingarian, Igor V; Silchenko, Olga K; Moiseev, Alexey V; Borisov, Svyatoslav B

    2016-01-01

    Although thick stellar discs are detected in nearly all edge-on disc galaxies, their formation scenarios still remain a matter of debate. Due to observational difficulties, there is a lack of information about their stellar populations. Using the Russian 6-m telescope BTA we collected deep spectra of thick discs in three edge-on S0-a disc galaxies located in different environments: NGC4111 in a dense group, NGC4710 in the Virgo cluster, and NGC5422 in a sparse group. We see intermediate age (4-5 Gyr) metal rich ([Fe/H] $\\sim$ -0.2 - 0.0 dex) stellar populations in NGC4111 and NGC4710. On the other hand, NGC5422 does not harbour young stars, its disc is thick and old (10 Gyr), without evidence for a second component, and its $\\alpha$-element abundance suggests a 1.5-2 Gyr long formation epoch implying its formation at high redshift. Our results suggest the diversity of thick disc formation scenarios.

  14. Dynamic, six-axis stiffness matrix characteristics of the intact intervertebral disc and a disc replacement.

    Science.gov (United States)

    Holsgrove, Timothy P; Gill, Harinderjit S; Miles, Anthony W; Gheduzzi, Sabina

    2015-11-01

    Thorough pre-testing is critical in assessing the likely in vivo performance of spinal devices prior to clinical use. However, there is a lack of data available concerning the dynamic testing of lumbar (porcine model) total disc replacements in all six axes under preload conditions. The aim of this study was to provide new data comparing porcine lumbar spinal specimen stiffness between the intact state and after the implantation of an unconstrained total disc replacement, in 6 degrees of freedom. The dynamic, stiffness matrix testing of six porcine lumbar isolated disc specimens was completed using triangle waves at a test frequency of 0.1 Hz. An axial preload of 500 N was applied during all testing. Specimens were tested both in the intact condition and after the implantation of the total disc replacement. Sixteen key stiffness terms were identified for the comparison of the intact and total disc replacement specimens, comprising the 6 principal stiffness terms and 10 key off-axis stiffness terms. The total disc replacement specimens were significantly different to the intact specimens in 12 of these key terms including all six principal stiffness terms. The implantation of the total disc replacement resulted in a mean reduction in the principal stiffness terms of 100%, 91%, and 98% in lateral bending, flexion-extension, and axial rotation, respectively. The novel findings of this study have demonstrated that the unconstrained, low-friction total disc replacement does not replicate the stiffness of the intact specimens. It is likely that other low-friction total disc replacements would produce similar results due to stiffness being actively minimised as part of the design of low-friction devices, without the introduction of stiffening elements or mechanisms to more accurately replicate the mechanical properties of the natural intervertebral disc. This study has demonstrated, for the first time, a method for the quantitative comparative mechanical function

  15. The role of disc self-gravity in circumbinary planet systems - I. Disc structure and evolution

    Science.gov (United States)

    Mutter, Matthew M.; Pierens, Arnaud; Nelson, Richard P.

    2017-03-01

    We present the results of two-dimensional hydrodynamic simulations of self-gravitating circumbinary discs around binaries whose parameters match those of the circumbinary planet-hosting systems Kepler-16, Kepler-34 and Kepler-35. Previous work has shown that non-self-gravitating discs in these systems form an eccentric precessing inner cavity due to tidal truncation by the binary, and planets which form at large radii migrate until stalling at this cavity. Whilst this scenario appears to provide a natural explanation for the observed orbital locations of the circumbinary planets, previous simulations have failed to match the observed planet orbital parameters. The aim of this work is to examine the role of self-gravity in modifying circumbinary disc structure as a function of disc mass, prior to considering the evolution of embedded circumbinary planets. In agreement with previous work, we find that for disc masses between one and five times the minimum mass solar nebula (MMSN), disc self-gravity affects modest changes in the structure and evolution of circumbinary discs. Increasing the disc mass to 10 or 20 MMSN leads to two dramatic changes in disc structure. First, the scale of the inner cavity shrinks substantially, bringing its outer edge closer to the binary. Secondly, in addition to the eccentric inner cavity, additional precessing eccentric ring-like features develop in the outer regions of the discs. If planet formation starts early in the disc lifetime, these changes will have a significant impact on the formation and evolution of planets and precursor material.

  16. Evolution from protoplanetary to debris discs: The transition disc around HD 166191

    CERN Document Server

    Kennedy, G M; Lisse, C M; Ménard, F; Sitko, M L; Wyatt, M C; Bayliss, D D R; DeMeo, F E; Crawford, K B; Kim, D L; Rudy, R J; Russell, R W; Sibthorpe, B; Skinner, M A; Zhou, G

    2013-01-01

    HD 166191 has been identified by several studies as hosting a rare and extremely bright warm debris disc with an additional outer cool disc component. However, an alternative interpretation is that the star hosts a disc that is currently in transition between a full gas disc and a largely gas-free debris disc. With the help of new optical to mid-IR spectra and Herschel imaging, we argue that the latter interpretation is supported in several ways: i) we show that HD 166191 is co-moving with the ~4 Myr-old Herbig Ae star HD 163296, suggesting that the two have the same age, ii) the disc spectrum of HD 166191 is well matched by a standard radiative transfer model of a gaseous protoplanetary disc with an inner hole, and iii) the HD 166191 mid-IR silicate feature is more consistent with similarly primordial objects. We note some potential issues with the debris disc interpretation that should be considered for such extreme objects, whose lifetime at the current brightness is mush shorter than the stellar age, or i...

  17. A Simulation Model of Focus and Radial Servos in Compact Disc Players with Disc Surface Defects

    DEFF Research Database (Denmark)

    Odgaard, Peter Fogh; Stoustrup, Jakob; Andersen, Palle;

    2004-01-01

    Compact Disc players have been on the market in more than two decades.As a consequence most of the control servo problems have been solved. A large remaining problem to solve is the handling of Compact Discs with severe surface defects like scratches and fingerprints. This paper introduces a method...

  18. Stem cell horizons in intervertebral disc degeneration

    Directory of Open Access Journals (Sweden)

    Joseph Ciacci

    2009-01-01

    Full Text Available Joseph Ciacci1, Allen Ho1,2, Christopher P Ames3, Rahul Jandial41Division of Neurosurgery, University of California, San Diego, La Jolla, California, USA; 2Del E Webb Neurosciences, Aging and Stem Cell Research Center, The Burnham Institute for Medical Research, La Jolla, California, USA; 3Department of Neurological Surgery, University of California, San Francisco, San Francisco, CA, USA; 4Division of Neurosurgery, Department of Surgery, City of Hope Cancer Center, Duarte, CA, USAAbstract: Intervertebral disc degeneration remains a pervasive and intractable disease arising from a combination of aging and stress on the back and spine. The growing field of regenerative medicine brings the promise of stem cells in the treatment of disc disease. Scientists and physicians hope to employ stem cells not only to stop, but also reverse degeneration. However, there are many important outstanding issues, including the hostile avascular, apoptotic physiological environment of the intervertebral disc, and the difficulty of obtaining mesenchymal stem cells, and directing them towards chondrocytic differentiation and integration within the nucleus pulposus of the disc. Given the recent advances in minimally invasive spine surgery, and developing body of work on stem cell manipulation and transplantation, stem cells are uniquely poised to bring about large-scale improvements in treatment and outcomes for degenerative disc disease. In this review we will first discuss the cellular and molecular factors influencing degeneration, and then examine the efficacy and difficulties of stem cell transplantation.Keywords: intervertebral disc degeneration, stem cells, disc disease, mesenchymal stem cells, stem cell transplantation

  19. Cervical disc hernia operations through posterior laminoforaminotomy

    Directory of Open Access Journals (Sweden)

    Coskun Yolas

    2016-01-01

    Full Text Available 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.

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

    Science.gov (United States)

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

    2015-06-01

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

  1. Effects of controlled dynamic disc distraction on degenerated intervertebral discs: an in vivo study on the rabbit lumbar spine model.

    Science.gov (United States)

    Kroeber, Markus; Unglaub, Frank; Guehring, Thorsten; Guegring, Thorsten; Nerlich, Andreas; Hadi, Tamer; Lotz, Jeffrey; Carstens, Claus

    2005-01-15

    An in vivo study on the rabbit lumbar spine model. Effects of temporary dynamic distraction on intervertebral discs were studied on the lumbar spine rabbit model to characterize the changes associated with disc distraction and to evaluate feasibility of temporary disc distraction to previously compressed discs in order to stimulate disc regeneration. Studies have shown that accelerated degeneration of the intervertebral disc results from altered mechanical loading conditions. The development of methods for the prevention of disc degeneration and the restoration of disc tissue that has already degenerated are needed. New Zealand white rabbits (n = 32) were used for this study. The rabbits were randomly assigned to one of five groups. In 12 animals, the discs were first loaded for 28 days using a custom-made external loading device to stimulate disc degeneration. After 28 days loading time, the discs in six animals were distracted for 7 days and in six animals for 28 days using the same external device, however, modified as dynamic distraction device. In six animals, the discs were distracted for 28 days without previous loading; and in six animals, the discs were loaded for 28 days and afterwards the loading device removed for 28 days for recovery without distraction. Six animals were sham operated. The external device was situated; however, the discs remained undistracted and they also served as controls. After 28 to 56 days loading and distraction time, the animals were killed and the lumbar spine was harvested for examination. Disc height, disc morphology, cell viability, relative neutral zone, and tangent modulus were measured. After 28 days of loading, the discs demonstrated a significant decrease in disc space. Histologically, disorganization of the architecture of the anulus occurred. The number of dead cells increased significantly in the anulus and cartilage endplate. These changes were reversible after 28 days of distraction. The disc thickness increased

  2. Dynamical instabilities in disc-planet interactions

    CERN Document Server

    Lin, Min-Kai

    2012-01-01

    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 si...

  3. Lubrication regimes in lumbar total disc arthroplasty.

    Science.gov (United States)

    Shaheen, A; Shepherd, D E T

    2007-08-01

    A number of total disc arthroplasty devices have been developed. Some concern has been expressed that wear may be a potential failure mode for these devices, as has been seen with hip arthroplasty. The aim of this paper was to investigate the lubrication regimes that occur in lumbar total disc arthroplasty devices. The disc arthroplasty was modelled as a ball-and-socket joint. Elastohydrodynamic lubrication theory was used to calculate the minimum film thickness of the fluid between the bearing surfaces. The lubrication regime was then determined for different material combinations, size of implant, and trunk velocity. Disc arthroplasties with a metal-polymer or metal-metal material combination operate with a boundary lubrication regime. A ceramic-ceramic material combination has the potential to operate with fluid-film lubrication. Disc arthroplasties with a metal-polymer or metal-metal material combination are likely to generate wear debris. In future, it is worth considering a ceramic-ceramic material combination as this is likely to reduce wear.

  4. Debris Discs: Modeling/theory review

    Science.gov (United States)

    Thébault, P.

    2012-03-01

    An impressive amount of photometric, spectroscopic and imaging observations of circumstellar debris discs has been accumulated over the past 3 decades, revealing that they come in all shapes and flavours, from young post-planet-formation systems like Beta-Pic to much older ones like Vega. What we see in these systems are small grains, which are probably only the tip of the iceberg of a vast population of larger (undetectable) collisionally-eroding bodies, leftover from the planet-formation process. Understanding the spatial structure, physical properties, origin and evolution of this dust is of crucial importance, as it is our only window into what is going on in these systems. Dust can be used as a tracer of the distribution of their collisional progenitors and of possible hidden massive pertubers, but can also allow to derive valuable information about the disc's total mass, size distribution or chemical composition. I will review the state of the art in numerical models of debris disc, and present some important issues that are explored by current modelling efforts: planet-disc interactions, link between cold (i.e. Herschel-observed) and hot discs, effect of binarity, transient versus continuous processes, etc. I will finally present some possible perspectives for the development of future models.

  5. The inner cavity of the circumnuclear disc

    CERN Document Server

    Blank, Marvin; Frank, Adam; Carroll-Nellenback, Jonathan J; Duschl, Wolfgang J

    2016-01-01

    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 second, 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 stabi...

  6. Crystallization of Self-Propelled Hard Discs

    Science.gov (United States)

    Briand, G.; Dauchot, O.

    2016-08-01

    We experimentally study the crystallization of a monolayer of vibrated discs with a built-in polar asymmetry, a model system of active liquids, and contrast it with that of vibrated isotropic discs. Increasing the packing fraction ϕ , the quasicontinuous crystallization reported for isotropic discs is replaced by a transition, or a crossover, towards a "self-melting" crystal. Starting from the liquid phase and increasing the packing fraction, clusters of dense hexagonal-ordered packed discs spontaneously form, melt, split, and merge, leading to a highly intermittent and heterogeneous dynamics. For a packing fraction larger than ϕ*, a few large clusters span the system size. The cluster size distribution is monotonically decreasing for ϕ ϕ*, and is a power law at the transition. The system is, however, never dynamically arrested. The clusters permanently melt from place to place, forming droplets of an active liquid which rapidly propagate across the system. This self-melting crystalline state subsists up to the highest possible packing fraction, questioning the stability of the crystal for active discs unless it is at ordered close packing.

  7. The quiescent phase of galactic disc growth

    CERN Document Server

    Aumer, Michael; Schönrich, Ralph

    2016-01-01

    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 ...

  8. Structures induced by companions in galactic discs

    CERN Document Server

    Kyziropoulos, P; Gravvanis, G; Patsis, P

    2016-01-01

    Using N-body simulations we study the structures induced on a galactic disc by repeated flybys of a companion in decaying eccentric orbit around the disc. Our system is composed by a stellar disc, bulge and live dark matter halo, and we study the system's dynamical response to a sequence of a companion's flybys, when we vary i) the disc's temperature (parameterized by Toomre's Q-parameter) and ii) the companion's mass and initial orbit. We use a new 3D Cartesian grid code: MAIN (Mesh-adaptive Approximate Inverse N-body solver). The main features of MAIN are reviewed, with emphasis on the use of a new Symmetric Factored Approximate Sparse Inverse (SFASI) matrix in conjunction with the multigrid method that allows the efficient solution of Poisson's equation in three space variables. We find that: i) companions need to be assigned initial masses in a rather narrow window of values in order to produce significant and more long-standing non-axisymmetric structures (bars and spirals) in the main galaxy's disc by t...

  9. Discs of Satellites: the new dwarf spheroidals

    CERN Document Server

    Metz, Manuel; Jerjen, Helmut

    2009-01-01

    The spatial distributions of the most recently discovered ultra faint dwarf satellites around the Milky Way and the Andromeda galaxy are compared to the previously reported discs-of-satellites (DoS) of their host galaxies. In our investigation we pay special attention to the selection bias introduced due to the limited sky coverage of SDSS. We find that the new Milky Way satellite galaxies follow closely the DoS defined by the more luminous dwarfs, thereby further emphasizing the statistical significance of this feature in the Galactic halo. We also notice a deficit of satellite galaxies with Galactocentric distances larger than 100 kpc that are away from the disc-of-satellites of the Milky Way. In the case of Andromeda, we obtain similar results, naturally complementing our previous finding and strengthening the notion that the discs-of-satellites are optical manifestations of a phase-space correlation of satellite galaxies.

  10. OPTIC DISC MELANOCYTOMA: A CASE REPORT

    Directory of Open Access Journals (Sweden)

    Sahiba Bedi

    2016-08-01

    Full Text Available Melanocytoma of the optic disc is a rare ophthalmic tumour that arises from melanocytes and is a variant of the melanocytic nevus. It occurs on the optic disc and often extends into the peripapillary retina and choroid. It appears as a dark brown or black lesion, typically small and is almost always unilateral. Although traditionally believed to be a relatively stationary lesion, it is now known to exhibit minor enlargement in 10–15% of cases and can cause minor visual loss by a variety of mechanisms. 1-2% cases can transform to malignant melanoma. We present a case report of a 65-year-old female whose dilated fundus examination of the right eye revealed a circular, pigmented and elevated lesion about 1.5 mm in size covering almost whole of the optic nerve head except for the superior rim, suggestive of optic disc melanocytoma.

  11. Signatures of massive collisions in debris discs

    CERN Document Server

    Kral, Quentin; Augereau, Jean-Charles; Boccaletti, Anthony; Charnoz, Sebastien

    2014-01-01

    Violent stochastic collisional events have been invoked as a possible explanation for some debris discs displaying pronounced asymmetries or having a great luminosity excess. So far, no thorough modelling of the consequences of such events has been carried out, mainly because of the extreme numerical challenge of coupling the dynamical and collisional evolution of dust. We perform the first fully self-consistent modelling of the aftermath of massive breakups in debris discs. We follow the collisional and dynamical evolution of dust released after the breakup of a Ceres-sized body at 6 AU from its central star. We investigate the duration, magnitude and spatial structure of the signature left by such a violent event, as well as its observational detectability. We use the recently developed LIDT-DD code (Kral et al., 2013), which handles the coupled collisional and dynamical evolution of debris discs. The main focus is placed on the complex interplay between destructive collisions, Keplerian dynamics and radiat...

  12. Black hole feedback from thick accretion discs

    CERN Document Server

    Sadowski, Aleksander; Abramowicz, Marek A; Narayan, Ramesh

    2015-01-01

    We study energy flows in geometrically thick accretion discs, both optically thick and thin, using general relativistic, three-dimensional simulations of black hole accretion flows. We find that for non-rotating black holes the efficiency of the total feedback from thick accretion discs is $3\\%$ - roughly half of the thin disc efficiency. This amount of energy is ultimately distributed between outflow and radiation, the latter scaling weakly with the accretion rate for super-critical accretion rates, and returned to the interstellar medium. Accretion on to rotating black holes is more efficient because of the additional extraction of rotational energy. However, the jet component is collimated and likely to interact only weakly with the environment, whereas the outflow and radiation components cover a wide solid angle.

  13. Satellites in discs regulating the accretion luminosity

    CERN Document Server

    Syer, D; Syer, Dave; Clarke, Cathie

    1995-01-01

    We demonstrate, using a simple analytic model, that the presence of a massive satellite can globally modify the structure and emission properties of an accretion disc to which it is tidally coupled. We show, using two levels of numerical approximation, that the analytic model gives reasonable results. The results are applicable to two astrophysical situations. In the case of an active galactic nucleus, we consider the case of a \\sim 10^3\\Msun compact companion to the central black-hole and show that it could modulate the emitted spectrum on a timescale of \\sim10^5 years. In the case of a T Tauri accretion disc, a satellite such as a sub-dwarf or giant planet could modify the disc spectral energy distribution over a substantial fraction of the T Tauri star lifetime.

  14. The debris disc around HIP 17439

    Science.gov (United States)

    Schüppler, Christian; Löhne, Torsten; Krivov, Alexander

    2013-07-01

    In the framework of the Herschel Open Time Key Programme DUNES the debris disc around the K2 V star HIP 17439 was observed. In PACS images the disc emission is spatially clearly extended. A simultaneous analysis of photometric observations and radial brightness profiles from the resolved images provides valuable hints for the disc structure. In an analytical model we adopted power laws for the size and radial distribution of the circumstellar dust and tested two different scenarios: (1) a broad dust ring with a radial extent of about 200AU, (2) two independent dust rings separated by a gap of several tens of AU. Both models fit the spectral energy distribution and the radial profiles quite well. In case (1) the parameters found are consistent with dust stemming from an outer planetesimal belt at ~140AU and strong transport mechanisms that drag the particles inward. Model (2) would imply two planetesimal belts, producing a narrow inner and wider outer distribution of dust.

  15. Effects of disc midplane evolution on CO snowline location

    Science.gov (United States)

    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.

  16. Effect of continuous lumbar traction on the size of herniated disc material in lumbar disc herniation.

    Science.gov (United States)

    Ozturk, Bulent; Gunduz, Osman Hakan; Ozoran, Kursat; Bostanoglu, Sevinc

    2006-05-01

    We investigated the effects of continuous lumbar traction in patients with lumbar disc herniation on clinical findings, and size of the herniated disc measured by computed tomography (CT). In this prospective, randomized, controlled study, 46 patients with lumbar disc herniation were included, and randomized into two groups as the traction group (24 patients), and the control group (22 patients). The traction group was given a physical therapy program and continuous lumbar traction. The control group was given the same physical therapy program without traction, for the same duration of time. Data for the clinical symptoms and signs were collected before and after the treatment together with calculation of a herniation index, from the CT images that showed the size of the herniated disc material. In the traction group, most of the clinical findings significantly improved with treatment. Size of the herniated disc material in CT decreased significantly only in the traction group. In the traction group the herniation index decreased from 276.6+/-129.6 to 212.5+/-84.3 with treatment (p0.05). Patients with greater herniations tended to respond better to traction. In conclusion, lumbar traction is both effective in improving symptoms and clinical findings in patients with lumbar disc herniation and also in decreasing the size of the herniated disc material as measured by CT.

  17. Cometary ices in forming protoplanetary disc midplanes

    Science.gov (United States)

    Drozdovskaya, Maria N.; Walsh, Catherine; van Dishoeck, Ewine F.; Furuya, Kenji; Marboeuf, Ulysse; Thiabaud, Amaury; Harsono, Daniel; Visser, Ruud

    2016-10-01

    Low-mass protostars are the extrasolar analogues of the natal Solar system. Sophisticated physicochemical models are used to simulate the formation of two protoplanetary discs from the initial prestellar phase, one dominated by viscous spreading and the other by pure infall. The results show that the volatile prestellar fingerprint is modified by the chemistry en route into the disc. This holds relatively independent of initial abundances and chemical parameters: physical conditions are more important. The amount of CO2 increases via the grain-surface reaction of OH with CO, which is enhanced by photodissociation of H2O ice. Complex organic molecules are produced during transport through the envelope at the expense of CH3OH ice. Their abundances can be comparable to that of methanol ice (few per cent of water ice) at large disc radii (R > 30 au). Current Class II disc models may be underestimating the complex organic content. Planet population synthesis models may underestimate the amount of CO2 and overestimate CH3OH ices in planetesimals by disregarding chemical processing between the cloud and disc phases. The overall C/O and C/N ratios differ between the gas and solid phases. The two ice ratios show little variation beyond the inner 10 au and both are nearly solar in the case of pure infall, but both are subsolar when viscous spreading dominates. Chemistry in the protostellar envelope en route to the protoplanetary disc sets the initial volatile and prebiotically significant content of icy planetesimals and cometary bodies. Comets are thus potentially reflecting the provenances of the midplane ices in the solar nebula.

  18. Cells and Biomaterials for Intervertebral Disc Regeneration

    CERN Document Server

    Grad, Sibylle

    2010-01-01

    Disorders related to the intervertebral disc (IVD) are common causes of morbidity and of severe life quality deterioration. IVD degeneration, although in many cases asymptomatic, is often the origin of painful neck and back diseases. In Western societies IVD related pain and disability account for enormous health care costs as a result of work absenteeism and thus lost production, disability benefits, medical and insurance expenses. Although only a small percentage of patients with disc disorders finally will undergo surgery, spinal surgery has been one of the fastest growing disciplines in th

  19. Natural course of lumber disc herniation

    Energy Technology Data Exchange (ETDEWEB)

    Tokioka, Takamitsu; Shimada, Kimio; Tanaka, Yuzo; Oshige, Toshihisa; Miyakoshi, Koichi [Okayama Rosai Hospital (Japan)

    1998-09-01

    Thirty-two cases of lumbar disc herniation were sequentially followed by MR imagings in order to ascertain its natural course. Herniation consisted of protrusion in 6 cases, extrusion in 13 cases, and sequestration in 13 cases. We analysed the durations until the herniation regressed more than 50% of its A-P diameter. The mean duration was 8.2 months for extrusion, and 5.3 months for sequestration. Only 2 cases of protrusion regressed within 12 months. Huge disc herniations with central protrusion in particular showed slight spontaneous regression. (author)

  20. Disc-Capped ZnO Nanocombs

    Institute of Scientific and Technical Information of China (English)

    LI Xin; XU chun-xiang; ZHU Guang-Ping; YANG Yi; LIU Jin-Ping; SUN Xiao-Wei; CUI Yi-Ping

    2007-01-01

    Nanocombs with a disc cap structure of ZnO have been synthesized on si substrates by using pure Zinc powders as the source materials based on a vapour-phase transport process.The morphology and the microstructure are investigated by a scanning electron microscopy and x-ray diffraction.Based on the transmission electron microscopy and selected area electron diffraction analysis,the growth directions of three representative parts,nanoribbon stem,nanorod branch and nanodisc cap of the nanocomb are revealed.The growth mechanism of the disc-capped nanocombs is discussed based on the self-catalyzed vapour-liquid-solid process.

  1. Multimedia Archiving: Videotape, Compact Disc (CD), Digital Versatile Disc (DVD), and Blu-Ray Disc (BD) Media

    Science.gov (United States)

    2010-02-01

    4 inch U-Matic or Betacam tapes, it is necessary to inventory the archives several times a year to determine which products are no longer worth...Philips, Samsung , Sharp, Sony, TDK and Thomson. The Blu-ray disc is based on an industry standard format supported by 190 companies and is written

  2. Be discs in binary systems I. Coplanar orbits

    CERN Document Server

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

    2016-01-01

    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, eccentricity) and disc (viscosity) parameters affect the disc structure in coplanar systems. We simulate such binaries with the use of a smoothed particle hydrodynamics code. The main effects of the secondary on the disc are its truncation and the accumulation of material inwards of truncation. 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 is smaller in size, more elongated and more massive for low viscosity parameter, small orbital separation and/or high mass ratio. Highly eccentric orbits are more complex, with the disc structure and total mass strongly dependent on the orbital phas...

  3. Relationship of condylar position to disc position and morphology

    Energy Technology Data Exchange (ETDEWEB)

    Incesu, L.; Taskaya-Yilmaz, N. E-mail: nergizy@omu.edu.tr; Oeguetcen-Toller, M.; Uzun, E

    2004-09-01

    Introduction/objective: The purpose of this study was to assess whether condylar position, as depicted by magnetic resonance imaging, was an indicator of disc morphology and position. Methods and material: One hundred and twenty two TMJs of 61 patients with temporomandibular joint disorder were examined. Condylar position, disc deformity and degree of anterior disc displacement were evaluated by using magnetic resonance imaging. Results and discussion: Posterior condyle position was found to be the main feature of temporomandibular joints with slight and moderate anterior disc displacement. No statistical significance was found between the condylar position, and reducing and nonreducing disc positions. On the other hand, superior disc position was found to be statistically significant for centric condylar position. Conclusion: It was concluded that posterior condyle position could indicate anterior disc displacement whereas there was no relation between the position of condyle and the disc deformity.

  4. ALGEBROIDAL FUNCTION AND ITS DERIVED FUNCTION IN UNIT CIRCULAR DISC

    Institute of Scientific and Technical Information of China (English)

    Huo Yingying; Sun Daochun

    2009-01-01

    In this article, the authors define the derived function of an algeboidal function in the unit disc, prove it is an algabriodal function, and study the order of algebroidal function and that of its derived function in unit circular disc.

  5. Post-Main Sequence Evolution of Debris Discs

    CERN Document Server

    Bonsor, Amy

    2010-01-01

    The population of debris discs on the main sequence is well constrained, however very little is known about debris discs around evolved stars. In this work we provide a theoretical framework that considers the effects of stellar evolution on debris discs; firstly considering the evolution of an individual disc from the main sequence through to the white dwarf phase, then extending this to the known population of debris discs around main sequence A stars. It is found that discs around evolved stars are harder to detect than on the main sequence. In the context of our models discs should be detectable with Herschel or Alma on the giant branch, subject to the uncertain effect of sublimation on the discs. The best chances are for hot young white dwarfs, fitting nicely with the observations e.g the helix nebula (Su et al. 2007) and 9 systems presented by Chu & Bilikova.

  6. Temporomandibular joint disc; a proposed histopathological degeneration grading score system

    OpenAIRE

    2010-01-01

    Summary. Aims: The purpose of this study was to draw up a TMJ disc histopathological score that is a semiquantitative transcription of the entire spectrum of TMJ disc degenerative diseases related to changes in disc tissue, and then validate the proposed grading, in order to contribute to a standardized histopathological diagnosis. Methods: Sections from sixty two temporomandibular joint disc specimens affected by tissue degenerative changes and stained with Hematox...

  7. MRI and discography in traumatic intervertebral disc lesions

    Energy Technology Data Exchange (ETDEWEB)

    Ghanem, Nadir; Uhl, Markus; Elgeti, Florian; Pache, Gregor; Kotter, Elmar; Langer, Mathias [University Hospital Freiburg, Departments of Diagnostic Radiology, Freiburg (Germany); Mueller, Christoph; Markmiller, Max [University Hospital Freiburg, Traumatology, Freiburg (Germany)

    2006-11-15

    In this study we evaluated magnetic resonance imaging (MRI) in trauma patients for assessing traumatised adjacent discs of fractured vertebrae before dorsoventral stabilisation. In a prospective study, MRI of 54 discs was performed with a 1.5-T MRI unit. The preoperative MRI with sagittal T1-W-SE and T2-W-TSE was compared to intraoperative discography, which was carried out on both intervertebral discs adjacent to the fractured vertebrae. Signal alterations, morphological changes in the adjacent discs, fractured vertebrae and associated ligament injuries were evaluated. In 47/54 (87%) of the intervertebral discs, the results of both imaging findings were concordant. The discs adjoining vertebral fractures were normal in 18 cases. Regarding the positive concordant imaging findings, MRI and discography revealed traumatised adjacent cranial and caudal discs in 22 discs. In 7 cases, only the cranial adjacent disc was affected. Moreover, 17 cases of intradiscal bleeding, 13 intraosseous herniations into the fractured vertebrae and 20 anuluar tears were visualised in MRI. Associated ligament injuries were detected in 18 cases. Findings were discordant in eight discs. In six discs, MRI was abnormal, demonstrating signal alterations suggestive of positive imaging findings, whereas discography demonstrated no disc injury. MRI failed to detect disc injury in two discs, whereas discography was positive, showing an irregular intradiscal contrast media distribution. MRI, as a non-invasive method for assessing fractures of the thoraco-lumbar spine, may detect traumatised adjacent intervertebral discs. MRI is superior to intraoperative discography. The performance of MRI of the thoraco-lumbar spine is recommended before dorsoventral stabilisation in trauma patients, as it can reveal additional preoperative information such as fractures, disc and associated ligament injuries. (orig.)

  8. INJURIES IN DISC GOLF - A DESCRIPTIVE CROSS-SECTIONAL STUDY

    DEFF Research Database (Denmark)

    Rahbek, Martin Amadeus; Nielsen, Rasmus Oestergaard

    2016-01-01

    BACKGROUND: Disc golf is rapidly increasing in popularity and more than two million people are estimated to regularly participate in disc golf activities. Despite this popularity, the epidemiology of injuries in disc golf remains under reported. PURPOSE: The purpose of the present study was to in...

  9. Morning glory disc anomaly with Chiari type I malformation.

    Science.gov (United States)

    Arlow, Tim; Arepalli, Sruthi; Flanders, Adam E; Shields, Carol L

    2014-04-30

    Morning glory disc anomaly is a rare optic nerve dysplasia associated with various neovascular abnormalities. Due to these associations, children with morning glory disc anomaly have brain imaging and angiography to detect other congenital defects. The authors report the case of an infant with morning glory disc anomaly and coexisting Chiari type I malformation.

  10. Review of gas and dust in debris discs

    Science.gov (United States)

    Kral, Q.

    2016-12-01

    This proceeding summarises a talk given on the state-of-the-art of debris disc modelling. We first review the basics of debris disc physics, which is followed by a short overview of the state-of-the-art in terms of modelling dust and gas in debris disc systems.

  11. Review of gas and dust in debris discs

    OpenAIRE

    Kral, Quentin

    2016-01-01

    This proceeding summarises a talk given on the state-of-the-art of debris disc modelling. We first review the basics of debris disc physics, which is followed by a short overview of the state-of-the-art in terms of modelling dust and gas in debris disc systems.

  12. A method for quantitative measurement of lumbar intervertebral disc structures

    DEFF Research Database (Denmark)

    Tunset, Andreas; Kjær, Per; Samir Chreiteh, Shadi

    2013-01-01

    There is a shortage of agreement studies relevant for measuring changes over time in lumbar intervertebral disc structures. The objectives of this study were: 1) to develop a method for measurement of intervertebral disc height, anterior and posterior disc material and dural sac diameter using MRI...

  13. Review of gas and dust in debris discs

    CERN Document Server

    Kral, Quentin

    2016-01-01

    This proceeding summarises a talk given on the state-of-the-art of debris disc modelling. We first review the basics of debris disc physics, which is followed by a short overview of the state-of-the-art in terms of modelling dust and gas in debris disc systems.

  14. MOND predictions of 'halo' phenomenology in disc galaxies

    NARCIS (Netherlands)

    Milgrom, M; Sanders, RH

    2005-01-01

    We examine two corollaries of MOND pertaining to properties of the equivalent dark matter halo. MOND predicts for pure exponential discs a tight relation involving the halo and disc scalelengths and the mean acceleration in the disc, which we find to test favourably against the Verheijen sample of

  15. Demographics of Transition Discs in Ophiuchus and Taurus

    CERN Document Server

    Najita, Joan R; Muzerolle, James

    2015-01-01

    Transition disc systems are young stars that appear to be on the verge of dispersing their protoplanetary discs. We explore the nature of these systems by comparing the stellar accretion rates and disc masses of transition discs and normal T Tauri stars in Taurus and Ophiuchus. After controlling for the known dependencies of stellar accretion rate and disc mass and on age, stellar accretion rate on stellar mass, and disc mass on the presence of stellar or sub-stellar companions, we find that the normal T Tauri stars show a trend of stellar accretion rate increasing with disc mass. The transition discs tend to have higher average disc masses than normal T Tauri stars as well as lower accretion rates than normal T Tauri stars of the same disc mass. These results are most consistent with the interpretation that the transition discs have formed objects massive enough to alter the accretion flow, i.e., single or multiple giant planets. Several Ophiuchus T Tauri stars that are not known transition disc systems also...

  16. Prognosis of intervertebral disc loss from diagnosis of degenerative disc disease

    Science.gov (United States)

    Li, S.; Lin, A.; Tay, K.; Romano, W.; Osman, Said

    2015-03-01

    Degenerative Disc Disease (DDD) is one of the most common causes of low back pain, and is a major factor in limiting the quality of life of an individual usually as they enter older stages of life, the disc degeneration reduces the shock absorption available which in turn causes pain. Disc loss is one of the central processes in the pathogenesis of DDD. In this study, we investigated whether the image texture features quantified from magnetic resonance imaging (MRI) could be appropriate markers for diagnosis of DDD and prognosis of inter-vertebral disc loss. The main objective is to use simple image based biomarkers to perform prognosis of spinal diseases using non-invasive procedures. Our results from 65 subjects proved the higher success rates of the combination marker compared to the individual markers and in the future, we will extend the study to other spine regions to allow prognosis and diagnosis of DDD for a wider region.

  17. SCANNING TUNNELING MICROSCOPY STUDIES ON OPTICAL DISC

    Institute of Scientific and Technical Information of China (English)

    徐磊; 顾冬红; 等

    1994-01-01

    Scanning tunneling microscope(STM) is used to investigate the optical dise.The areas with and without data stampers are all observedcarefully.Three-dimensional images of the disc surface clearly demonstrate the period.depth of the grooves and the shape of data stampers.Some phenomena of STM imaging are also discussed.

  18. Low back pain and degenerative disc disease

    Directory of Open Access Journals (Sweden)

    Jandrić Slavica

    2006-01-01

    Full Text Available Introduction. Various clinical conditions can cause low back pain, and in most cases it is of a degenerative origin. Degenerative disc disease is a common condition which affects young to middle-aged men and women equally. Changes in the mechanical properties of the disc lead to degenerative arthritis in the intervertebral joints, osteophytes, and narrowing the intervertebral foramen or the spinal canal. Pathophysiology. Degenerative cascade, described by Kirkaldy-Willis, is the widely accepted pathophysiologic model describing the degenerative process as it affects the lumbar spine in 3 phases. Diagnosis. There are two forms of low back pain secondary to degenerative disc disease: a lumbalgia and b lumbar radiculopathy. Limitation of movement, problems with balance, pain, loss of reflexes in the extremities, muscle weakness, loss of sensation or other signs of neurological damage can be found on physical examination. For accurate diagnosis, it is often necessary to combine clinical examination and sophisticated technology. Treatment. Coservative treatment consists of rest, physical therapy, pharmacological therapy and injection therapy. Physical rehabilitation with active patient participation is a key approach to treatment of patients with discogenic pain. Physical therapy, occupational therapy and kinesitherapy are important for improving muscle strength, endurance, and flexibility. Disc surgery is performed if surgical intervention is required. .

  19. Cometary ices in forming protoplanetary disc midplanes

    CERN Document Server

    Drozdovskaya, Maria N; van Dishoeck, Ewine F; Furuya, Kenji; Marboeuf, Ulysse; Thiabaud, Amaury; Harsono, Daniel; Visser, Ruud

    2016-01-01

    Low-mass protostars are the extrasolar analogues of the natal Solar System. Sophisticated physicochemical models are used to simulate the formation of two protoplanetary discs from the initial prestellar phase, one dominated by viscous spreading and the other by pure infall. The results show that the volatile prestellar fingerprint is modified by the chemistry en route into the disc. This holds relatively independent of initial abundances and chemical parameters: physical conditions are more important. The amount of CO2 increases via the grain-surface reaction of OH with CO, which is enhanced by photodissociation of H2O ice. Complex organic molecules are produced during transport through the envelope at the expense of CH3OH ice. Their abundances can be comparable to that of methanol ice (few % of water ice) at large disc radii (R > 30 AU). Current Class II disc models may be underestimating the complex organic content. Planet population synthesis models may underestimate the amount of CO2 and overestimate CH3...

  20. Front view of the innermost endcap disc.

    CERN Multimedia

    Maximilien Brice

    2006-01-01

    This ~750 tonne disc is covered with muon chambers (copper-coloured) with the hadron calorimeter and Preshower support cone at the centre. The image was taken through one of the barrel rings; some barrel muon chambers can be seen at the edges of the picture. Bigger files available (39 Mpx)

  1. Front view of the innermost endcap disc.

    CERN Multimedia

    Maximilien Brice

    2006-01-01

    This ~750 tonne disc is covered with muon chambers (copper-coloured) with the hadron calorimeter and Preshower support cone at the centre. The image was taken through one of the barrel rings; some barrel muon chambers can be seen at the edges of the picture.

  2. Disc degeneration-related clinical phenotypes.

    Science.gov (United States)

    Battié, Michele C; Lazáry, Aron; Fairbank, Jeremy; Eisenstein, Stephen; Heywood, Chris; Brayda-Bruno, Marco; Varga, Péter Pál; McCall, Iain

    2014-06-01

    The phenotype, or observable trait of interest, is at the core of studies identifying associated genetic variants and their functional pathways, as well as diagnostics. Yet, despite remarkable technological developments in genotyping and progress in genetic research, relatively little attention has been paid to the equally important issue of phenotype. This is especially true for disc degeneration-related disorders, and the concept of degenerative disc disease, in particular, where there is little consensus or uniformity of definition. Greater attention and rigour are clearly needed in the development of disc degeneration-related clinical phenotypes if we are to see more rapid advancements in knowledge of this area. When selecting phenotypes, a basic decision is whether to focus directly on the complex clinical phenotype (e.g. the clinical syndrome of spinal stenosis), which is ultimately of interest, or an intermediate phenotype (e.g. dural sac cross-sectional area). While both have advantages, it cannot be assumed that associated gene variants will be similarly relevant to both. Among other considerations are factors influencing phenotype identification, comorbidities that are often present, and measurement issues. Genodisc, the European research consortium project on disc-related clinical pathologies has adopted a strategy that will allow for the careful characterisation and examination of both the complex clinical phenotypes of interest and their components.

  3. Global Structure of Magnetorotationally Turbulent Protoplanetary Discs

    CERN Document Server

    Flaig, M; Kley, W; Kissmann, R

    2011-01-01

    The aim of the present paper is to investigate the spatial structure of a protoplanetary disc whose dynamics is governed by magnetorotational turbulence. We perform a series of local 3D chemo-radiative MHD simulations located at different radii of a disc which is twice as massive as the standard minimum mass solar nebula of Hayashi (1981). The ionisation state of the disc is calculated by including collisional ionisation, stellar X-rays, cosmic rays and the decay of radionuclides as ionisation sources, and by solving a simplified chemical network which includes the effect of the absorption of free charges by {\\mu}m-sized dust grains. In the region where the ionisation is too low to assure good coupling between matter and magnetic fields, a non-turbulent central "dead zone" forms, which ranges approximately from a distance of 2 AU to 4 AU from the central star. The approach taken in the present work allows for the first time to derive the global spatial structure of a protoplanetary disc from a set of physical...

  4. Kinematic structures in galactic disc simulations

    NARCIS (Netherlands)

    Roca-F� brega, S.; Romero-Gómez, M.; Figueras, F.; Antoja Castelltort, Teresa; Valenzuela, O.; Henney, W.J.; Torres-Peimbert, S.

    2011-01-01

    N-body and test particle simulations have been used to characterize the stellar streams in the galactic discs of Milky Way type galaxies. Tools such as the second and third order moments of the velocity ellipsoid and clustering methods -EM-WEKA and FoF- allow characterizing these kinematic structure

  5. Spiral waves in accretion discs - observations

    CERN Document Server

    Steeghs, D

    2000-01-01

    I review the observational evidence for spiral structure in the accretion discs of cataclysmic variables (CVs). Doppler tomography is ideally suited to resolve and map such co-rotating patterns and allows a straightforward comparison with theory. The dwarf nova IP Pegasi presents the best studied case, carrying two spiral arms in a wide range of emission lines throughout its outbursts. Both arms appear at the locations where tidally driven spiral waves are expected, with the arm closest to the gas stream weaker in the lines compared to the arm closest to the companion. Eclipse data indicates sub-Keplerian velocities in the outer disc. The dramatic disc structure changes in dwarf novae on timescales of days to weeks, provide unique opportunities for our understanding of angular momentum transport and the role of density waves on the structure of accretion discs. I present an extension to the Doppler tomography technique that relaxes one of the basic assumptions of tomography, and is able to map modulated emiss...

  6. Frictional Torque on a Rotating Disc

    Science.gov (United States)

    Mungan, Carl E.

    2012-01-01

    Resistance to motion often includes a dry frictional term independent of the speed of an object and a fluid drag term varying linearly with speed in the viscous limit. (At higher speeds, quadratic drag can also occur.) Here, measurements are performed for an aluminium disc mounted on bearings that is given an initial twist and allowed to spin…

  7. Eclipse Mapping: Astrotomography of Accretion Discs

    Science.gov (United States)

    Baptista, Raymundo

    The Eclipse Mapping Method is an indirect imaging technique that transforms the shape of the eclipse light curve into a map of the surface brightness distribution of the occulted regions. Three decades of application of this technique to the investigation of the structure, the spectrum and the time evolution of accretion discs around white dwarfs in cataclysmic variables have enriched our understanding of these accretion devices with a wealth of details such as (but not limited to) moving heating/cooling waves during outbursts in dwarf novae, tidally-induced spiral shocks of emitting gas with sub-Keplerian velocities, elliptical precessing discs associated to superhumps, and measurements of the radial run of the disc viscosity through the mapping of the disc flickering sources. This chapter reviews the principles of the method, discusses its performance, limitations, useful error propagation procedures, as well as highlights a selection of applications aimed at showing the possible scientific problems that have been and may be addresses with it.

  8. Nonsurgical management of disc-interference disorders.

    Science.gov (United States)

    Okeson, J P

    1991-01-01

    Disc-interference disorders are a group of intracapsular problems that make up one category of temporomandibular disorders. The dental profession's understanding of these disorders has changed greatly in recent years. This article reviews current concepts regarding the diagnosis and management of these disorders as revealed through recent clinical studies.

  9. Intervertebral Disc Herniation Treated by Comprehensive Therapy

    Institute of Scientific and Technical Information of China (English)

    SUN Yu; HUANG Guo-qi

    2007-01-01

    In the treatment of 169 cases of the patients sick with intervertebral disc hemiation by integrated application of acupuncture therapy,Chinese massage therapy and herbal fumigation method.the results showed cure in 129 cases.improvement in 33 cases and failure in 7 cases,and the total effective rate was 95.9%.

  10. Scaling from discs to pleated devices.

    Science.gov (United States)

    Giglia, Sal; Yavorsky, David

    2007-01-01

    Membrane discs offer a convenient format for evaluating membrane performance in normal flow filtration. However, while pleated devices of different sizes tend to scale in close proportion to their contained areas, they do not necessarily scale in direct proportion from flat discs. The objectives of this study are to quantify differences in performance among sterilizing-grade membrane devices as a function of device type and size, to develop an understanding of the factors that affect device scalability, and to develop a mathematical model to predict a cartridge-to-disc scalability factor based on membrane properties and porous support properties and dimensions. Measured and predicted normalized water permeability scalability factors for seven types of pleated cartridges, including 0.1-micro and 0.2-micro rated PES, and 0.2-micro rated polyvinylidene fluoride (PVDF) sterilizing-grade filters in nominal 1-inch to 5-inch lengths, were determined. The results of this study indicate that pleated cartridge performance can be closely predicted based on 47-mm disc performance provided that a number of measured device parameters are properly accounted for, most importantly parasitic pressure losses in the filter device and plumbing connections, intrinsic membrane variability, true effective device filtration area, and the hydraulic properties of all porous support materials. Throughput scalability factors (discs to devices) tend to converge towards unity, especially for highly plugging streams. As the membrane fouls, the resistance through the membrane dominates other resistances, so the flux scales more linearly with membrane area and the overall scaling factor becomes close to one. The results of throughput tests on seven different cartridge types and five different challenge streams (with widely varying fouling characteristics) show that most of the throughput scaling factors were within +/-10% of 1.0. As part of this study, the effects of pressure and temperature were

  11. Quality control of cast brake discs

    Directory of Open Access Journals (Sweden)

    M. Stawarz

    2008-04-01

    Full Text Available The largest industrial application so far have the gray cast irons which are characterized by low tensile and bending strength, while at the same time they have good ultimate comprehensive strength. Additionally, the fatigue strength of gray cast irons is comparatively low and they are only to some extend sensitive for the surface waters effects. Cast iron is the material, which is comparatively easy to be processed, and for this reason – it is not expensive. Brake discs are exploited in particularly hard conditions. They must be resistant both against the thermal fatigue and abrasion wearing (at dry friction as well as against seizing, corrosion and mechanical load [1-3]. The gray cast iron, better than other materials, fulfills all the requirements necessary for making the material for the casts resistant against such tough conditions. This work reflects the researches aiming to define the quality of cast brake discs (ventilated and non-ventilated ones upon a period of their exploitation in real conditions. The following researches were performed: evaluations of the disc surface condition, measurement of disc thickness, examination of run – out flank and metallographic analysis. In order to more detailed recognition of mechanisms and reasons of brake discs wearing in real conditions, one should conduct additional examinations: computer analysis of the microstructure, chemical composition analysis, etc., as well as study of the technology of their production in foundries, where they are manufactured [4]. By obtaining the full set of the mentioned above data one can draw final conclusions and remove causes of possible defects.

  12. The Role of Disc Self-Gravity in Circumbinary Planet Systems: I. Disc Structure and Evolution

    CERN Document Server

    Mutter, Matthew M; Nelson, Richard P

    2016-01-01

    We present the results of 2-dimensional hydrodynamic simulations of self-gravitating circumbinary discs around binaries whose parameters match those of the circumbinary planet-hosting systems Kepler-16, -34 and -35. Previous work has shown that non-self-gravitating discs in these systems form an eccentric precessing inner cavity due to tidal truncation by the binary, and planets which form at large radii migrate until stalling at this cavity. While this scenario appears to provide a natural explanation for the observed orbital locations of the circumbinary planets, previous simulations have failed to match the observed planet orbital parameters. The aim of this work is to examine the role of self-gravity in modifying circumbinary disc structure as a function of disc mass, prior to considering the evolution of embedded circumbinary planets. In agreement with previous work, we find that for disc masses between 1--5 times the minimum mass solar nebula (MMSN), disc self-gravity affects modest changes in the struc...

  13. Inner Disc Obscuration in GRS 1915+105 Based on Relativistic Slim Disc Model

    CERN Document Server

    Vierdayanti, K; Mineshige, S; Bursa, M

    2013-01-01

    We study the observational signatures of the relativistic slim disc of 10 M_sun black hole, in a wide range of mass accretion rate, mdot, dimensionless spin parameter, a_ast, and viewing angle, i. In general, the innermost temperature, T_in increases with the increase of i for a fixed value of mdot and a_ast, due to the Doppler effect. However, for i > 50 and mdot > mdot_turn, T_in starts to decrease with the increase of mdot. This is a result of self-obscuration -- the radiation from the innermost hot part of the disc is blocked by the surrounding cooler part. The value of mdot_turn and the corresponding luminosities depend on a_ast and i. Such obscuration effects cause an interesting behavior on the disc luminosity (L_disc) -- T_in plane for high inclinations. In addition to the standard-disc branch which appears below mdot_turn and which obeys L_disc propto T_in^4 -relation, another branch above mdot_turn, which is nearly horizontal, may be observed at luminosities close to the Eddington luminosity. We sho...

  14. Structure Formation in Gas-Rich Galactic Discs with Finite Thickness: From Discs to Rings

    CERN Document Server

    Behrendt, Manuel; Schartmann, Marc

    2014-01-01

    Gravitational instabilities play an important role in structure formation of gas-rich high-redshift disc galaxies. In this paper, we revisit the axisymmetric perturbation theory and the resulting growth of structure, by taking the realistic thickness of the disc into account. In the unstable regime, which corresponds for thick discs to a Toomre parameter below the critical value Q=0.696, we find a fastest growing perturbation wavelength that is always a factor 1.93 times larger than in the classical razor-thin disc approximation. This result is independent of the adopted disc scale height and by this independent of temperature and surface density. In order to test the analytical theory, we compare it with a high resolution hydrodynamical simulation of an isothermal gravitationally unstable gas disc with the typical vertical sech density profile and study its break-up into rings that subsequently fragment into dense clumps. In the first phase rings form, that organise themselves discretely, with distances corr...

  15. Disc space distraction is a potent risk factor for adjacent disc disease after PLIF.

    Science.gov (United States)

    Kaito, Takashi; Hosono, Noboru; Fuji, Takeshi; Makino, Takahiro; Yonenobu, Kazuo

    2011-11-01

    We reported that excessive disc space distraction caused by insertion of large cages during posterior lumbar interbody fusion (PLIF) combined with pedicle screws (PS) induces adjacent segment disease (ASD). Spinous process plate (SPP) is known to allow cage subsidence when used in PLIF, since they cannot share vertical loads. We therefore hypothesize that the incidence of ASD after PLIF with SPP should be lower than that after PLIF with PS due to this loss of disc space distraction. Radiographic ASD is defined as development of spondylolisthesis > 3 mm, decrease in disc height > 3 mm, or intervertebral angle at flexion lesser than -5°. Symptomatic ASD is defined by a decrease of ≥ 4 points in Japanese Orthopedic Association score. One hundred and thirty patients with L4 spondylolisthesis were treated with either PLIF with SPP (n = 45) or PLIF with PS (n = 85) and followed up for a minimum of 2 years (mean, 39.0 months). L4-5 disc space distraction in the SPP group was significantly smaller (0.4 mm) as compared to the PS group (1.8 mm). The incidence of clinical ASD in the SPP group (2%, 1/45) was also significantly less than that in the PS group (15%, 13/85). Multivariate analysis showed that disc space distraction was the most significant risk factor. Among various risk factors for ASD after PLIF, the excessive distraction of disc space proved to be a potent risk factor for ASD.

  16. Differentiation of glaucomatous optic discs with different appearances using optic disc topography parameters: The Glaucoma Stereo Analysis Study

    Science.gov (United States)

    Tanito, Masaki; Nitta, Koji; Katai, Maki; Kitaoka, Yasushi; Yokoyama, Yu; Omodaka, Kazuko; Nakazawa, Toru

    2017-01-01

    The Glaucoma Stereo Analysis Study (GSAS) is a multicenter collaborative study of the characteristics of glaucomatous optic disc morphology using a stereo fundus camera. Using GSAS dataset, the formulas for predicting different glaucomatous optic disc appearances were established. The GSAS dataset containing three-dimensionally-analyzed optic disc topographic parameters from 187 eyes with primary open-angle glaucoma was assessed with discrimination analyses to obtain formulas predictive of glaucomatous optic disc appearances: focal ischemic (FI); generalized enlargement (GE), myopic glaucomatous (MY), and senile sclerotic (SS). Using 38 optic disc parameters-substituted discrimination analyses with a stepwise forward-selection method, six parameters (temporal and nasal rim-disc ratios, mean cup depth, height variation contour, disc tilt angle, and rim decentering absolute) were selected into the formulas. The area under the receiver operating characteristic curves for predicting the four disc types with established formulas were 0.88, 0.91, 0.93, and 0.86 for FI, MY, SS, and GE, respectively. Age, visual acuity, refractive error, glaucoma (normal or high-tension glaucoma), and baseline intraocular pressure differed significantly among the four optic disc types, suggesting the appearances represent different clinical glaucoma phenotypes. Using six optic disc topographic parameters obtained by stereo fundus camera, the GSAS classification formulas predicted and quantified each component of different optic disc appearances in each eye and provided a novel parameter to describe glaucomatous optic disc characteristics. PMID:28178303

  17. Counterrotating perfect fluid discs as sources of electrovacuum static spacetimes

    CERN Document Server

    García-Reyes, Gonzalo

    2008-01-01

    The interpretation of some electrovacuum spacetimes in terms of counterrotating perfect fluid discs is presented. The interpretation is mades by means of an "inverse problem" approach used to obtain disc sources of known static solutions of the Einstein-Maxwell equations. In order to do such interpretation, a detailed study is presented of the counterrotating model (CRM) for generic electrovacuum static axially symmetric relativistic thin discs with nonzero radial pressure. Four simple families of models of counterrotating charged discs based on Chazy-Curzon-type, Zipoy-Voorhees-type, Bonnor-Sackfield-type, and charged and magnetized Darmois electrovacuum metrics are considered where we obtain some discs with a CRM well behaved.

  18. Do observations reveal accretion discs in intermediate polars

    Energy Technology Data Exchange (ETDEWEB)

    Hellier, C. (University Coll., London (UK). Mullard Space Science Lab.)

    1991-08-15

    It has been proposed that intermediate polars do not accrete through discs and that they may not possess discs. Observations of eclipses and emission lines provide strong evidence that discs are present in many intermediate polars, although it is less clear whether the accretion flows through these discs. An analysis of the EXOSAT database shows that many systems have orbital and beat period modulations which are small compared to the spin-pulses, suggesting disc accretion. There are, though, exceptions, notably TX Col where dominant orbital and beat period modulations indicate discless accretion. (author).

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

    CERN Document Server

    Doğan, Suzan; King, Andrew; Price, Daniel J

    2015-01-01

    Accretion discs are common in binary systems, and they are often found to be misaligned with respect to the binary orbit. The gravitational torque from a companion induces nodal precession in misaligned disc orbits. We calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. For typical parameters precession wins: the disc breaks into distinct planes that precess effectively independently. We run hydrodynamical simulations to check these results, and confirm that disc breaking is widespread and generally enhances accretion on to the central object. This applies in many cases of astrophysical accretion, e.g. supermassive black hole binaries and X--ray binaries.

  20. The Disc-Jet Relation in Strong-Lined Blazars

    OpenAIRE

    D'Elia, V.; Padovani, P.; Landt, H.

    2002-01-01

    The relation between accretion disc (thermal emission) and jet (non-thermal emission) in blazars is still a mystery as, typically, the beamed jet emission swamps the disc even in the ultraviolet band where disc emission peaks. In this paper we estimate the accretion disc component for 136 flat-spectrum radio quasars selected from the Deep X-ray Radio Blazar Survey. We do this by deriving the accretion disc spectrum from the mass and accretion rate onto the central black hole for each object, ...

  1. Spinning out of control: wall turbulence over rotating discs

    CERN Document Server

    Wise, Daniel J; Ricco, Pierre

    2014-01-01

    The friction drag reduction in a turbulent channel flow generated by surface-mounted rotating disc actuators is investigated numerically. The wall arrangement of the discs has a complex and unexpected effect on the flow. For low disc-tip velocities, the drag reduction scales linearly with the percentage of the actuated area, whereas for higher disc-tip velocity the drag reduction can be larger than the prediction found through the linear scaling with actuated area. For medium disc-tip velocities, all the cases which display this additional drag reduction exhibit stationary-wall regions between discs along the streamwise direction. This effect is caused by the viscous boundary layer which develops over the portions of stationary wall due to the radial flow produced by the discs. For the highest disc-tip velocity, the drag reduction even increases by halving the number of discs. The power spent to activate the discs is instead independent of the disc arrangement and scales linearly with the actuated area for al...

  2. MR image assessment of disc configuration and degree of anterior disc displacement in internal derangement related to age

    Energy Technology Data Exchange (ETDEWEB)

    Igarashi, Chinami; Kobayashi, Kaoru; Imanaka, Masahiro; Yuasa, Masao; Yamamoto, Akira [Tsurumi Univ., Yokohama (Japan). School of Dental Medicine

    1999-03-01

    This study was designed to evaluate the configuration of the articular disc and degree of anterior disc displacement on magnetic resonance (MR) imagings in temporomandibular joints (TMJs) with internal derangement. A total of 363 joints diagnosed as having anterior disc displacement with reduction (ADD w R) and 523 joints diagnosed as having anterior disc displacement without reduction (ADD wo R) by MR imaging were examined. These joints did not show severe osseous changes on the condylar head or glenoid fossa. We assessed the configuration of the articular disc and degree of anterior disc displacement. In the ADD w R group, 82.6% of the articular discs showed biconcave configuration; enlargement of the posterior band in 4.6%, biconvex configuration in 0.5%, and others in 10.7%. Moreover 62.5% of the discs showed a slight degree of anterior disc displacement; were 27.2% moderately displaced and were 10.2% severe displaced. The prevalence of slightly displaced discs was higher in the TMJs of cases over 50 years of age than in cases under 30 years in the ADD w R group. On the other hand, in the ADD wo R group 35.9% of the articular discs showed biconcave configuration; enlargement of the posterior band in 12.6%, biconvex configuration in 25.4%, and others in 22.3%. Furthermore, 4.4% of the discs were slightly displaced; 43.9% moderately displaced and 51.6% were severely displaced. The prevalence of severely displaced and deformed discs in joints of cases over 40 years of age was high in the ADD wo R group. The prevalence of slightly displaced biconcave discs was higher in the ADD w R group. The other hand, the prevalence of severely displaced deformed discs was higher in the ADD wo R group. MR findings of internal derangement of the TMJ were found to be significantly correlated with age. (author)

  3. Dispersing the Gaseous Protoplanetary Disc and Halting Type II Migration

    CERN Document Server

    Lecar, M

    2003-01-01

    More than 30 extra-solar Jupiter-like planets have shorter periods than the planet Mercury. It is generally accepted that they formed further out, and migrated inwards. In order to be driven by tidal torques from the gaseous disc, the disc exterior to the planet had to contain about a planetary mass. The fact that the planets stopped migrating means that their outer disc was removed. We suggest that the outer disc was accreted by the planet. In this scenario, the endgame is a race. The planet survives if it accretes its outer disc before being accreted by the star. The winner is determined solely by the ratio of the mass of the outer disc to the local surface density of the disc.

  4. Optimum design of inhomogeneous rotating discs under secondary creep

    Energy Technology Data Exchange (ETDEWEB)

    Farshi, Behrooz [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846 (Iran, Islamic Republic of)], E-mail: Farshi@iust.ac.ir; Bidabadi, Jalal [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846 (Iran, Islamic Republic of)

    2008-07-15

    Rotating discs commonly used in the aerospace industry often operate under high mechanical stresses due to centrifugal forces, while subject to high temperature gradients. High stresses and temperatures lead to creep in such rotating disc applications. This problem is particularly important in turbine discs under continuous operation. Since such discs are subject to secondary creep effects during most of their useful lives, it is important that they be optimized for minimum weight for the steady-state creep stresses. In this investigation, by considering the variable physical properties of the rotating disc materials under a high temperature gradient, a procedure for weight minimization for the steady-state creep stresses is proposed. The method aims to design the disc thickness profile so as to have minimum weight while the equivalent secondary creep stresses of the rotating disc under a high temperature gradient at all points simultaneously approach but do not exceed an allowable stress. An example is given to illustrate the method.

  5. Images of accretion discs. 1. The eclipse mapping method

    Energy Technology Data Exchange (ETDEWEB)

    Horne, K.

    1985-03-01

    A method of mapping the surface brightness distributions of accretion discs in eclipsing cataclysmic binaries is described and tested with synthetic eclipse data. Accurate synthetic light curves are computed by numerical simulation of the accretion disc eclipse, and images of the disc are reconstructed by maximum entropy methods. The conventional definition of entropy leads to a distorted image of the disc. A modified form of entropy, sensitive to the aximuthal structure of the image but not to its radial profile, suppresses azimuthal structure but correctly recovers the radial structure of the accretion disc. This eclipse mapping method permits powerful tests of accretion disc theory by deriving the spatial structure of discs from observational data with a minimum of model-dependent assumptions.

  6. Vertical shear instability in accretion disc models with radiation transport

    CERN Document Server

    Stoll, Moritz H R

    2014-01-01

    The origin of turbulence in accretion discs is still not fully understood. While the magneto-rotational instability is considered to operate in sufficiently ionized discs, its role in the poorly ionized protoplanetary disc is questionable. Recently, the vertical shear instability (VSI) has been suggested as a possible alternative. Our goal is to study the characteristics of this instability and the efficiency of angular momentum transport, in extended discs, under the influence of radiative transport and irradiation from the central star. We use multi-dimensional hydrodynamic simulations to model a larger section of an accretion disc. First we study inviscid and weakly viscous discs using a fixed radial temperature profile in two and three spatial dimensions. The simulations are then extended to include radiative transport and irradiation from the central star. In agreement with previous studies we find for the isothermal disc a sustained unstable state with a weak positive angular momentum transport of the o...

  7. On the Eddington limit for relativistic accretion discs

    CERN Document Server

    Abolmasov, Pavel

    2015-01-01

    Standard accretion disc model relies upon several assumptions, the most important of which is geometrical thinness. Whenever this condition is violated, new physical effects become important such as radial energy advection and mass loss from the disc. These effects are important, for instance, for large mass accretion rates when the disc approaches its local Eddington limit. In this work, we study the upper limits for standard accretion disc approximation and find the corrections to the standard model that should be considered in any model aiming on reproducing the transition to super-Eddington accretion regime. First, we find that for thin accretion disc, taking into account relativistic corrections allows to increase the local Eddington limit by about a factor of two due to stronger gravity in General Relativity (GR). However, violation of the local Eddington limit also means large disc thickness. To consider consequently the disc thickness effects, one should make assumptions upon the two-dimensional rotat...

  8. Accreting planets as dust dams in `transition' discs

    CERN Document Server

    Owen, James E

    2014-01-01

    We investigate under what circumstances an embedded planet in a protoplanetary disc may sculpt the dust distribution such that it observationally presents as a `transition' disc. We concern ourselves with `transition' discs that have large holes ($\\gtrsim 10$ AU) and high accretion rates ($\\sim 10^{-9}-10^{-8}$ M$_\\odot$ yr$^{-1}$). Particularly, those discs which photoevaporative models struggle to explain. Assuming the standard picture for how massive planets sculpt their parent discs, along with the observed accretion rates in `transition' discs, we find that the accretion luminosity from the forming planet is significant, and can dominate over the stellar luminosity at the gap edge. This planetary accretion luminosity can apply a significant radiation pressure to small ($s\\lesssim 1\\mu$m) dust particles provided they are suitably decoupled from the gas. Secular evolution calculations that account for the evolution of the gas and dust components in a disc with an embedded, accreting planet, show that only ...

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

    CERN Document Server

    Malanchev, K L; Shakura, N I

    2016-01-01

    The vertical structure of stationary thin accretion discs is calculated from the energy balance equation with heat generation due to microscopic ion viscosity {\\eta} and electron heat conductivity {\\kappa}, 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 dependen...

  10. Disc heating: possible link between weak bars and superthin galaxies

    CERN Document Server

    Saha, Kanak

    2014-01-01

    The extreme flatness of stellar discs in superthin galaxies is puzzling and the apparent dearth of these objects in cosmological simulation poses challenging problem to the standard cold dark matter paradigm. Irrespective of mergers or accretion that a galaxy might be going through, stars are heated as they get older while they interact with the spirals and bars which are ubiquitous in disc galaxies -- leading to a puffed up stellar disc. It remains unclear how superthin galaxies maintain their thinness through the cosmic evolution. We follow the internal evolution of a sample of 16 initially extremely thin stellar discs using collisionless N-body simulation. All of these discs eventually form a bar in their central region. Depending on the initial condition, some of these stellar discs readily form strong bars while others grow weak bars over secular evolution time scale. We show that galaxies with strong bars heat the stars very efficiently, eventually making their stellar discs thicker. On the other hand, ...

  11. Queixas auditivas de disc jockeys da cidade de Recife Auditory complaints in disc jockeys in Recife

    Directory of Open Access Journals (Sweden)

    Eliza Maia de Britto Macedo

    2011-06-01

    Full Text Available OBJETIVO: investigar a ocorrência de queixas auditivas em disc jockeys da cidade de Recife/PE. MÉTODOS: foi realizada uma entrevista com 30 disc jockeys, com idade entre 19 e 28 anos, abordando informações ocupacionais, conhecimentos gerais sobre o ruído e queixas auditivas (diminuição da acuidade auditiva, desconforto a sons intensos, zumbido, sensação de ouvido abafado e otalgia. A análise foi realizada por meio de abordagem quantitativa, utilizando o teste estatístico t-student. RESULTADOS: dentre os dados mais relevantes, destacam-se: 46,7% dos disc jockeys apresentaram, espontaneamente, queixas auditivas, em especial, a diminuição da acuidade auditiva (relatada por todos os sujeitos; 14 disc jockeys (46,67% referiram desconforto a sons intensos e 13 (43,33% mencionaram zumbido. Todos afirmaram ter conhecimento sobre os riscos do ruído para a saúde auditiva, mas 76,7% não realizam qualquer medida preventiva de suas consequências. A perda auditiva foi referida pelos sujeitos como o principal risco da exposição a níveis intensos de pressão sonora. CONCLUSÃO: todos os disc jockeys apresentaram queixa de perda auditiva e, entre as demais queixas auditivas, destacaram-se o desconforto a sons intensos e o zumbido. Tendo em vista a irreversibilidade da perda auditiva induzida por elevados níveis de pressão sonora, os disc jockeys devem ser periodicamente avaliados a fim de que se confirme ou não a perda auditiva de que se queixaram e, caso ela exista, deve ser monitorada para que seja passível de intervenção pelo fonoaudiólogo. Desta forma, percebe-se a necessidade de atuação da Fonoaudiologia junto aos disc jockeys, uma vez que poder-se-á propiciar a otimização do exercício profissional com o mínimo de risco possível.PURPOSE: to investigate the occurrence of auditory complaints in disc jockeys from the city of Recife/PE. METHODS: an interview was carried through with 30 disc jockeys aged between 19 and 48 years

  12. MR imaging of degenerative disc disease

    Energy Technology Data Exchange (ETDEWEB)

    Farshad-Amacker, Nadja A., E-mail: nadja.farshad@usz.ch [Institute of Diagnostic and Interventional Radiology, University Hospital of Zurich, Zurich (Switzerland); Farshad, Mazda [Department of Orthopaedic Surgery, Balgrist University Hospital, Zurich (Switzerland); Winklehner, Anna; Andreisek, Gustav [Institute of Diagnostic and Interventional Radiology, University Hospital of Zurich, Zurich (Switzerland)

    2015-09-15

    Highlights: • This systematic literature review summarizes the current knowledge on MR imaging in degenerative disc disease. • Different classification systems for segmental spine degeneration are summarized. • It outlines the diagnostic limitations of MR imaging. - Abstract: Magnet resonance imaging (MRI) is the most commonly used imaging modality for diagnosis of degenerative disc disease (DDD). Lack of precise observations and documentation of aspects within the complex entity of DDD might partially be the cause of poor correlation of radiographic findings to clinical symptoms. This literature review summarizes the current knowledge on MRI in DDD and outlines the diagnostic limitations. The review further sensitizes the reader toward awareness of potentially untended aspects of DDD and the interaction of DDD and endplate changes. A summary of the available classifications for DDD is provided.

  13. Magnetised accretion discs in Kerr spacetimes

    CERN Document Server

    Ranea-Sandoval, Ignacio F

    2014-01-01

    We study the effect caused by external magnetic fields on the observed thermal spectra and iron line profiles of thin accretion discs formed around Kerr black holes and naked singularities. We aim to provide a tool that can be used to estimate the presence of magnetic fields in the neighbourhood of a compact object and to probe the cosmic censorship conjecture in these particular astrophysical environments. We developed a numerical scheme able to calculate thermal spectra of magnetised Page-Thorne accretion discs formed around rotating black holes and naked singularities as seen by an arbitrary distant observer. We incorporated two different magnetic field configurations: uniform and dipolar, using a perturbative scheme in the coupling constant between matter and magnetic field strength. Under the same assumptions, we obtained observed synthetic line profiles of the 6.4 keV fluorescent iron line. We show that an external magnetic field produces potentially observable modifications on the thermal energy spectr...

  14. Diaphragm paralysis from cervical disc lesions.

    Science.gov (United States)

    Cloward, R B

    1988-01-01

    An opera singer, who "made her living with her diaphragm", developed a post-traumatic unilateral radiculopathy due to cervical disc lesions, C3 to C6. During one year of severe neck and left arm pain she gradually lost the ability to sing difficult operatic passages which brought an end to her music career. Following a three level anterior cervical decompression and fusion, the neck and arm pain was immediately relieved. One week later her voice and singing ability returned to its full strength and power permitting her to resume her activities as a vocalist. The diagnosis of paresis of the left hemi-diaphragm as part of the cervical disc syndrome was implied by postoperative retrospective inference.

  15. Slim Discs with Varying Accretion Rates

    Institute of Scientific and Technical Information of China (English)

    JIAO Cheng-Liang; LU Ju-Fu

    2009-01-01

    @@ It was revealed in our previous studies that there exists a maximal possible accretion rate for slim discs with constant accretion rates because the correctly calculated vertical gravitational force can only gather some limited amount of accreted matter. Here we show that when the accretion rate is not constant and instead decreases with decreasing radius because of outflows, such that the amount of accreted matter is adjusted to be within the allowed limit, global slim disc solutions can be constructed even for the case that accretion rates at large radii apparently exceed the maximal possible value. This result further demonstrates that outflows seem to be unavoidable for accretion flows with large accretion rates at large radii.

  16. Grand Challenges in Protoplanetary Disc Modelling

    Science.gov (United States)

    Haworth, Thomas J.; Ilee, John D.; Forgan, Duncan H.; Facchini, Stefano; Price, Daniel J.; Boneberg, Dominika M.; Booth, Richard A.; Clarke, Cathie J.; Gonzalez, Jean-François; Hutchison, Mark A.; Kamp, Inga; Laibe, Guillaume; Lyra, Wladimir; Meru, Farzana; Mohanty, Subhanjoy; Panić, Olja; Rice, Ken; Suzuki, Takeru; Teague, Richard; Walsh, Catherine; Woitke, Peter; Community authors

    2016-10-01

    The Protoplanetary Discussions conference-held in Edinburgh, UK, from 2016 March 7th-11th-included several open sessions led by participants. This paper reports on the discussions collectively concerned with the multi-physics modelling of protoplanetary discs, including the self-consistent calculation of gas and dust dynamics, radiative transfer, and chemistry. After a short introduction to each of these disciplines in isolation, we identify a series of burning questions and grand challenges associated with their continuing development and integration. We then discuss potential pathways towards solving these challenges, grouped by strategical, technical, and collaborative developments. This paper is not intended to be a review, but rather to motivate and direct future research and collaboration across typically distinct fields based on community-driven input, to encourage further progress in our understanding of circumstellar and protoplanetary discs.

  17. Grand challenges in protoplanetary disc modelling

    CERN Document Server

    Haworth, Thomas J; Forgan, Duncan H; Facchini, Stefano; Price, Daniel J; authors, Community; Boneberg, Dominika M; Booth, Richard A; Gonzalez, Jean-François; Hutchison, Mark A; Laibe, Guillaume; Meru, Farzana; Mohanty, Subhanjoy; Panić, Olja; Rice, Ken; Walsh, Catherine; Woitke, Peter

    2016-01-01

    The Protoplanetary Discussions conference --- held in Edinburgh, UK, from 7th-11th March 2016 --- included several open sessions led by participants. This paper reports on the discussions collectively concerned with the multiphysics modelling of protoplanetary discs, including the self-consistent calculation of gas and dust dynamics, radiative transfer and chemistry. After a short introduction to each of these disciplines in isolation, we identify a series of burning questions and grand challenges associated with their integration, which are not necessarily achievable in the short-to-medium term. We then discuss potential pathways towards solving these challenges, grouped by strategical, technical and collaborative developments. This paper is not intended to be a review, but rather to motivate and direct future research and collaboration across typically distinct fields based on community driven input, to encourage further progress in our understanding of circumstellar and protoplanetary discs.

  18. On the convective overstability in protoplanetary discs

    CERN Document Server

    Latter, Henrik

    2015-01-01

    This paper explores the driving of low-level hydrodynamical activity in protoplanetary-disc dead zones. A small adverse radial entropy gradient, ordinarily stabilised by rotation, excites oscillatory convection (`convective overstability') when thermal diffusion, or cooling, is neither too strong nor too weak. I revisit the linear theory of the instability, discuss its prevalence in protoplanetary discs, and show that unstable modes are exact nonlinear solutions in the local Boussinesq limit. Overstable modes cannot grow indefinitely, however, as they are subject to a secondary parametric instability that limits their amplitudes to relatively low levels. If parasites set the saturation level of the ensuing turbulence then the convective overstability is probably too weak to drive significant angular momentum transport or to generate vortices. But I also discuss an alternative, and far more vigorous, saturation route that generates radial `layers' or `zonal flows' (witnessed also in semiconvection). Numerical ...

  19. Rapid planetesimal formation in turbulent circumstellar discs

    CERN Document Server

    Johansen, Anders; Mac Low, Mordecai-Mark; Klahr, Hubert; Henning, Thomas; Youdin, Andrew

    2007-01-01

    The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies (Safronov 1969). How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem (Dominik et al. 2007): boulders stick together poorly (Benz 2000), and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas (Weidenschilling 1977). Gravitational collapse of the solid component has been suggested to overcome this barrier (Safronov 1969, Goldreich & Ward 1973, Youdin & Shu 2002). Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer (Weidenschilling & Cuzzi 1993, Dominik et al. 2007), but turbulence must be present to explain observed gas accretion in protostellar discs (Hartmann 1998). Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The bou...

  20. Intervertebral disc calcification in a child

    Directory of Open Access Journals (Sweden)

    Ahemad Athar

    2008-01-01

    Full Text Available Disc calcification in children is a rare condition of which only approximately 200 cases have been reported worldwide and one from India and we report one such case. A five year-old boy presented with neck pain, torticollis and limitations of cervical motions following a fall while playing 3 months back. He had low grade fever cervical lymphadenopthy, paraspinal muscle spasm. His blood counts and ESR was raised. Fine needle aspiration cytology of lymph node revealed reactive lymphadenitis. His cervical radiograph slowed calcification of C 6-7. MRI scan showed hypointense signals in C6-C7 and D5-D6 disc on both T1 and T2 W images. Cerebrospinal fluid examination was normal. He improved on analgesics, bed rest and cervical traction.

  1. Tourette's syndrome with cervical disc herniation.

    Science.gov (United States)

    Lin, Jainn-Jim; Wang, Huei-Shyong; Wong, Mun-Ching; Wu, Chieh-Tsai; Lin, Kuang-Lin

    2007-03-01

    Tourette's syndrome is manifested in a broad spectrum of motor, vocal, and behavioral disturbances. Movement disorders, such as tics, may contribute to the development of cervical myelopathy owing to the effects of involuntary movements on the neck. However, the association of cervical myelopathy with motor tics of the head and neck is rare. We report here a case of a violent, repetitive neck extension due to Tourette's syndrome that developed cervical myelopathy caused by cervical disc herniation.

  2. Influence of degenerative changes of intervertebral disc

    Directory of Open Access Journals (Sweden)

    WANG Yi

    2012-04-01

    Full Text Available 【Abstract】Objective: To investigate the material properties of normal and degenerated intervertebral discs (IVDs and examine the effect of degenerative changes on IVD pathology. Methods: A computer-based online search was under-taken to identify English articles about material properties of IVDs published from January 1950 to 2011 in PubMed database. The retrieved keywords included material properties, intervertebral disc and degeneration. Based on the principles of reliability, advancement and efficiency, the obtained data were primarily examined, and the original source was retrieved to read the full-text. Repetitive articles were excluded. The data of material properties of normal and degenerated IVDs were summarized and analyzed by meta-analysis. Results: The data of Young's modulus, Poisson's ratio, shear modulus, hydraulic permeability and intradiscal pres-sure of normal and degenerated IVDs were obtained. Com-pared with normal IVDs, the Young's modulus and shear modulus of annulus fibrosus and nucleus pulposus were higher in degenerated IVDs, the Poisson's ratio was lower while the hydraulic permeability and intradiscal pressure were higher. Besides, the degeneration-related alterations in IVDs had an influence both on itself and other spinal structures, leading to diseases such as bulging disc, discogenic pain and spinal stenosis. Meanwhile, the heavy mechanical loading and injury indicated important pathways to IVD degeneration. Conclusions: To a certain extent, the degenerative changes of IVD influence its material properties. And the degeneration-related alterations of composition can cause structural failure of IVDs, leading to injuries and diseases. Key words: Intervertebral disc; Mechanical phenomena; Degeneration; Elastic modulus; Permeability; Pathology

  3. Development of an Optical Disc Recorder

    Science.gov (United States)

    1977-02-01

    the disc. The phase locked ioop (PLL) must be capable of remaining locked even when the data rate read f rom the disk differs from its nomina l value...n about ±8 to 10 kHz of the nomina l v a l u e . Othe rwi se - , t he loop b a n d w i d t h becom es excess ive ly large j u s t to acc omm

  4. Detection of Surface Defects on Compact Discs

    DEFF Research Database (Denmark)

    Odgaard, Peter Fogh; Stoustrup, Jakob; Andersen, Palle

    2007-01-01

    Online detection of surface defects on optical discs is of high importance for the accommodation schemes handling these defects. These surface defects introduce fault components to the position measurements of focus and radial tracking positions. The respective controllers will accordingly try to...... in order to inspect the importance and consequences of the size of the detection delay, from which it can be seen that focus and radial position errors increase significantly due to the fault as the detection delay increases....

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

    Science.gov (United States)

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

    2016-01-01

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

  6. Satellites in Discs: Regulating the Accretion Luminosity

    OpenAIRE

    Syer, Dave; Clarke, Cathie

    1995-01-01

    We demonstrate, using a simple analytic model, that the presence of a massive satellite can globally modify the structure and emission properties of an accretion disc to which it is tidally coupled. We show, using two levels of numerical approximation, that the analytic model gives reasonable results. The results are applicable to two astrophysical situations. In the case of an active galactic nucleus, we consider the case of a $\\sim 10^3\\Msun$ compact companion to the central black-hole and ...

  7. Ni-based superalloys for turbine discs

    Science.gov (United States)

    Furrer, David; Fecht, Hans

    1999-01-01

    Superalloys have been developed for specific, specialized properties and applications. One of the main applications for nickel-based superalloys is gas-turbine-engine disc components for land-based power generation and aircraft propulsion. Turbine engines create harsh environments for materials due to the high operating temperatures and stress levels. Hence, as described in this article, many alloys used in the high-temperature turbine sections of these engines are very complex and highly optimized.

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

    CERN Document Server

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

    2014-01-01

    We develop a chemical evolution model in order to study the star formation history of the Milky Way. Our model assumes that the Milky Way is formed from a closed box-like system in the inner regions, while the outer parts of the disc experience some accretion. Unlike the usual procedure, we do not fix the star formation prescription (e.g. Kennicutt law) in order to reproduce the chemical abundance trends. Instead, we fit the abundance trends with age in order to recover the star formation history of the Galaxy. Our method enables one to recover with unprecedented accuracy the star formation history of the Milky Way in the first Gyrs, in both the inner (R9-10kpc) discs as sampled in the solar vicinity. We show that, in the inner disc, half of the stellar mass formed during the thick disc phase, in the first 4-5 Gyr. This phase was followed by a significant dip in the star formation activity (at 8-9 Gyr) and a period of roughly constant lower level star formation for the remaining 8 Gyr. The thick disc phase ha...

  9. Chipping machines: disc and drum energy requirements

    Directory of Open Access Journals (Sweden)

    Alessio Facello

    2013-09-01

    Full Text Available Air pollution and fossil fuel reserves exhaustion are increasing the importance of the biomass-derived products, in particular wood, as source of clean and renewable energy for the production of electricity or steam. In order to improve the global efficiency and the entire production chain, we have to evaluate the energetic aspects linked to the process of transformation, handling and transport of these materials. This paper reports results on a comparison between two chippers of similar size using different cutting technology: disc and drum tool respectively. During trials, fuel consumption, PTO torque and speed, processing time and weight of processed material were recorded. Power demand, fuel consumption, specific energy and productivity were computed. The machine was fed with four different feedstock types (chestnut logs, poplar logs, poplar branches, poplar sawmill residues. 15 repetitions for each combination of feedstock-tool were carried out. The results of this study show that the disc tool requires, depending on the processed material, from 12 to 18% less fuel per unit of material processed than the drum tool, and consequently, from 12 to 16% less specific energy. In particular, the highest difference between tools was found in branches processing whereas the smallest was in poplar logs. Furthermore the results of the investigation indicate, that, in testing conditions, the productivity of drum tool is higher (8% than disc tool.

  10. Testing hydrodynamics schemes in galaxy disc simulations

    Science.gov (United States)

    Few, C. G.; Dobbs, C.; Pettitt, A.; Konstandin, L.

    2016-08-01

    We examine how three fundamentally different numerical hydrodynamics codes follow the evolution of an isothermal galactic disc with an external spiral potential. We compare an adaptive mesh refinement code (RAMSES), a smoothed particle hydrodynamics code (SPHNG), and a volume-discretized mesh-less code (GIZMO). Using standard refinement criteria, we find that RAMSES produces a disc that is less vertically concentrated and does not reach such high densities as the SPHNG or GIZMO runs. The gas surface density in the spiral arms increases at a lower rate for the RAMSES simulations compared to the other codes. There is also a greater degree of substructure in the SPHNG and GIZMO runs and secondary spiral arms are more pronounced. By resolving the Jeans length with a greater number of grid cells, we achieve more similar results to the Lagrangian codes used in this study. Other alterations to the refinement scheme (adding extra levels of refinement and refining based on local density gradients) are less successful in reducing the disparity between RAMSES and SPHNG/GIZMO. Although more similar, SPHNG displays different density distributions and vertical mass profiles to all modes of GIZMO (including the smoothed particle hydrodynamics version). This suggests differences also arise which are not intrinsic to the particular method but rather due to its implementation. The discrepancies between codes (in particular, the densities reached in the spiral arms) could potentially result in differences in the locations and time-scales for gravitational collapse, and therefore impact star formation activity in more complex galaxy disc simulations.

  11. Spinning disc atomisation process: Modelling and computations

    Science.gov (United States)

    Li, Yuan; Sisoev, Grigory; Shikhmurzaev, Yulii

    2016-11-01

    The atomisation of liquids using a spinning disc (SDA), where the centrifugal force is used to generate a continuous flow, with the liquid eventually disintegrating into drops which, on solidification, become particles, is a key element in many technologies. Examples of such technologies range from powder manufacturing in metallurgy to various biomedical applications. In order to be able to control the SDA process, it is necessary to understand it as a whole, from the feeding of the liquid and the wave pattern developing on the disc to the disintegration of the liquid film into filaments and these into drops. The SDA process has been the subject of a number of experimental studies and some elements of it, notably the film on a spinning disc and the dynamics of the jets streaming out from it, have been investigated theoretically. However, to date there have been no studies of the process as a whole, including, most importantly, the transition zone where the film that has already developed a certain wave pattern disintegrates into jets that spiral out. The present work reports some results of an ongoing project aimed at producing a definitive map of regimes occurring in the SDA process and their outcome.

  12. Magnetically driven accretion in protoplanetary discs

    CERN Document Server

    Simon, Jacob B; Kunz, Matthew W; Armitage, Philip J

    2015-01-01

    We characterize magnetically driven accretion at radii between 1 au and 100 au in protoplanetary discs, using a series of local non-ideal magnetohydrodynamic (MHD) simulations. The simulations assume a Minimum Mass Solar Nebula (MMSN) disc that is threaded by a net vertical magnetic field of specified strength. Confirming previous results, we find that the Hall effect has only a modest impact on accretion at 30 au, and essentially none at 100 au. At 1-10 au the Hall effect introduces a pronounced bi-modality in the accretion process, with vertical magnetic fields aligned to the disc rotation supporting a strong laminar Maxwell stress that is absent if the field is anti-aligned. In the anti-aligned case, we instead find evidence for bursts of turbulent stress at 5-10 au, which we tentatively identify with the non-axisymmetric Hall-shear instability. The presence or absence of these bursts depends upon the details of the adopted chemical model, which suggests that appreciable regions of actual protoplanetary di...

  13. Time-dependence of non-planar accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Papaloizou, J.C.B. (Queen Mary Coll., London (UK). Dept. of Applied Mathematics); Pringle, J.E. (Amsterdam Univ. (Netherlands). Astronomical Inst.)

    1983-03-01

    Equations are derived which describe the time-dependence of a viscous, tilted accretion disc subject to external torques. A full hydrodynamical treatment is used and the equations linearized in terms of a small tilt. It is shown that previous attempts at deriving these equations are inadequate due to the inconsistency of some of the assumptions made. The behaviour of a tilted viscous disc is not simple to describe. Viscous forces tend to flatten the disc, but they also produce torques within the disc which induce local precession of disc elements. The main complication is that the horizontal motions induced in the disc by the tilt are resonantly driven so that their magnitude and phase are governed by the viscosity. This leads to the disc being smoothed on a time-scale faster than the usual viscous one. In order to obtain a simple diffusion equation governing the tilt angle ..beta.., it is necessary in a Keplerian disc that the viscosity parameter ..cap alpha.. be greater than the opening angle of the disc (H/R). If this condition is not satisfied consideration must be given to the proper dynamical modes of the disc, and the simple approach to the problem adopted here is inadequate.

  14. Dispersal of Gaseous Circumstellar Discs around High-Mass Stars

    CERN Document Server

    Shen, Y; Shen, Yue; Lou, Yu-Qing

    2006-01-01

    We study the dispersal of a gaseous disc surrounding a central high-mass stellar core once this circumstellar disc becomes fully ionized. If the stellar and surrounding EUV and X-ray radiations are so strong as to rapidly heat up and ionize the entire circumstellar disc as further facilitated by disc magnetohydrodynamic (MHD) turbulence, a shock can be driven to travel outward in the fully ionized disc, behind which the disc expands and thins. For an extremely massive and powerful stellar core, the ionized gas pressure overwhelms the centrifugal and gravitational forces in the disc. In this limit, we construct self-similar shock solutions for such an expansion and depletion phase. As a significant amount of circumstellar gas being removed, the relic disc becomes vulnerable to strong stellar winds and fragments into clumps. We speculate that disc disappearance happens rapidly, perhaps on a timescale of $\\sim 10^3-10^4\\hbox{yr}$ once the disc becomes entirely ionized sometime after the onset of thermal nuclear ...

  15. Effect of collagen fibre orientation on intervertebral disc torsion mechanics.

    Science.gov (United States)

    Yang, Bo; O'Connell, Grace D

    2017-07-21

    The intervertebral disc is a complex fibro-cartilaginous material, consisting of a pressurized nucleus pulposus surrounded by the annulus fibrosus, which has an angle-ply structure. Disc injury and degeneration are noted by significant changes in tissue structure and function, which significantly alters stress distribution and disc joint stiffness. Differences in fibre orientation are thought to contribute to changes in disc torsion mechanics. Therefore, the objective of this study was to evaluate the effect of collagen fibre orientation on internal disc mechanics under compression combined with axial rotation. We developed and validated a finite element model (FEM) to delineate changes in disc mechanics due to fibre orientation from differences in material properties. FEM simulations were performed with fibres oriented at [Formula: see text] throughout the disc (uniform by region and fibre layer). The initial model was validated by published experimental results for two load conditions, including [Formula: see text] axial compression and [Formula: see text] axial rotation. Once validated, fibre orientation was rotated by [Formula: see text] or [Formula: see text] towards the horizontal plane, resulting in a decrease in disc joint torsional stiffness. Furthermore, we observed that axial rotation caused a sinusoidal change in disc height and radial bulge, which may be beneficial for nutrient transport. In conclusion, including anatomically relevant fibre angles in disc joint FEMs is important for understanding stress distribution throughout the disc and will be important for understanding potential causes for disc injury. Future models will include regional differences in fibre orientation to better represent the fibre architecture of the native disc.

  16. Vortex stretching in self-gravitating protoplanetary discs

    Science.gov (United States)

    Regály, Zs.; Vorobyov, E.

    2017-10-01

    Horseshoe-shaped brightness asymmetries of several transitional discs are thought to be caused by large-scale vortices. Anticyclonic vortices efficiently collect dust particles, therefore they can play a major role in planet formation. Former studies suggest that the disc self-gravity weakens vortices formed at the edge of the gap opened by a massive planet in discs whose masses are in the range of 0.01 ≤ Mdisc/M* ≤ 0.1. Here, we present an investigation on the long-term evolution of the large-scale vortices formed at the viscosity transition of the discs' dead zone outer edge by means of two-dimensional hydrodynamic simulations taking disc self-gravity into account. We perform a numerical study of low-mass, 0.001 ≤ Mdisc/M* ≤ 0.01, discs, for which cases disc self-gravity was previously neglected. The large-scale vortices are found to be stretched due to disc self-gravity even for low-mass discs with Mdisc/M* ≳ 0.005, where initially the Toomre Q-parameter was ≲ 50 at the vortex distance. As a result of stretching, the vortex aspect ratio increases and a weaker azimuthal density contrast develops. The strength of the vortex stretching is proportional to the disc mass. The vortex stretching can be explained by a combined action of a non-vanishing gravitational torque caused by the vortex and the Keplerian shear of the disc. Self-gravitating vortices are subject to significantly faster decay than non-self-gravitating ones. We found that vortices developed at sharp viscosity transitions of self-gravitating discs can be described by a Goodman - Narayan - Goldreich (GNG) model as long as the disc viscosity is low, i.e. αdz ≤ 10-5.

  17. Segmental mobility, disc height and patient-reported outcomes after surgery for degenerative disc disease: a prospective randomised trial comparing disc replacement and multidisciplinary rehabilitation.

    Science.gov (United States)

    Johnsen, L G; Brinckmann, P; Hellum, C; Rossvoll, I; Leivseth, G

    2013-01-01

    This prospective multicentre study was undertaken to determine segmental movement, disc height and sagittal alignment after total disc replacement (TDR) in the lumbosacral spine and to assess the correlation of biomechanical properties to clinical outcomes.A total of 173 patients with degenerative disc disease and low back pain for more than one year were randomised to receive either TDR or multidisciplinary rehabilitation (MDR). Segmental movement in the sagittal plane and disc height were measured using distortion compensated roentgen analysis (DCRA) comparing radiographs in active flexion and extension. Correlation analysis between the range of movement or disc height and patient-reported outcomes was performed in both groups. After two years, no significant change in movement in the sagittal plane was found in segments with TDR or between the two treatment groups. It remained the same or increased slightly in untreated segments in the TDR group and in this group there was a significant increase in disc height in the operated segments. There was no correlation between segmental movement or disc height and patient-reported outcomes in either group.In this study, insertion of an intervertebral disc prosthesis TDR did not increase movement in the sagittal plane and segmental movement did not correlate with patient-reported outcomes. This suggests that in the lumbar spine the movement preserving properties of TDR are not major determinants of clinical outcomes.

  18. Continuum and line modelling of discs around young stars - I. 300000 disc models for HERSCHEL/GASPS

    Science.gov (United States)

    Woitke, P.; Pinte, C.; Tilling, I.; Ménard, F.; Kamp, I.; Thi, W.-F.; Duchêne, G.; Augereau, J.-C.

    2010-06-01

    We have combined the thermo-chemical disc code ProDiMo with the Monte Carlo radiative transfer code MCFOST to calculate a grid of ~300000 circumstellar disc models, systematically varying 11 stellar, disc and dust parameters including the total disc mass, several disc shape parameters and the dust-to-gas ratio. For each model, dust continuum and line radiative transfer calculations are carried out for 29 far-infrared, sub-mm and mm lines of [OI], [CII], 12CO and o/p-H2O under five inclinations. The grid allows us to study the influence of the input parameters on the observables, to make statistical predictions for different types of circumstellar discs and to find systematic trends and correlations between the parameters, the continuum fluxes and the line fluxes. The model grid, comprising the calculated disc temperature and chemical structures, the computed spectral energy distributions, line fluxes and profiles, will be used in particular for the data interpretation of the HERSCHEL open time-key program GASPS. The calculated line fluxes show a strong dependence on the assumed ultraviolet excess of the central star and on the disc flaring. The fraction of models predicting [OI] and [CII] fine-structure lines fluxes above HERSCHEL/PACS and SPICA/SAFARI detection limits is calculated as a function of disc mass. The possibility of deriving the disc gas mass from line observations is discussed.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1984-07-01

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

  20. Evolution of inclined planets in three-dimensional radiative discs

    CERN Document Server

    Bitsch, Bertram

    2011-01-01

    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. 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. The protoplanetary disc is modelled as a viscous gas where the internally produced dissipation is transported by radiation. For locally isothermal discs, we confirm previous results and find inclination damping and inward migration for planetary cores. For low inclinations i < 2 H/r, the damping is...

  1. Heritability of optic disc diameters: a twin study

    DEFF Research Database (Denmark)

    Drobnjak, Dragana; Taarnhøj, Nina Charlotte; Mitchell, Paul

    2011-01-01

    Purpose: To assess the relative influence of genetic and environmental factors on optic disc size and cup/disc ratio in healthy eyes. Methods: A sample of 55 monozygotic and 50 dizygotic healthy twin pairs aged 20-46, all having the same sex within pairs (47 pairs were male) had optic discs......: 20-45%). For cup/disc ratio, additive genetic and unshared environmental factors explained 66% (95% CI: 48-77%) and 34% (95% CI: 23-52%) of the variations, respectively. Discussion: In this healthy twin sample, we found that three quarters of the variations in vertical optic disc and optic cup...... measured from colour fundus photographs according to the Wisconsin Protocol. Structural equation modelling was used to estimate the relative contribution of genetic and environmental factors to the phenotype. Results: Disc dimensions did not vary significantly by age or sex. After adjusting for age and sex...

  2. [Research advances in animal models of intervertebral disc degeneration].

    Science.gov (United States)

    Zhang, Wenli; Liu, Hao; Li, Tanzhu

    2007-11-01

    To review the research advances in animal models of human disc degeneration. The relative articles in recent years were extensively reviewed. Studies both at home and abroad were analyzed and classified. The advantages and disadvantages of each method were compared. Studies were classified as either experimentally induced models or spontaneous models. The induced models were subdivided as mechanical (alteration of forces on the normal disc), structural (injury or chemical alteration) and genetically induced models. Spontaneous models included those animals that naturally developed degenerative disc disease. Animal model of intervertebral disc degeneration is an important path for revealing the pathogenesis of human disc degeneration, and play an important role in testing novel interventions. With recent advances in the relevance of animal models and humans, it has a great prospect in study of human disc degeneration.

  3. Advances in Susceptibility Genetics of Intervertebral Degenerative Disc Disease

    Directory of Open Access Journals (Sweden)

    Yin'gang Zhang, Zhengming Sun, Jiangtao Liu, Xiong Guo

    2008-01-01

    Full Text Available The traditional view that the etiology of lumbar disc herniation is primarily due to age, gender, occupation, smoking and exposure to vehicular vibration dominated much of the last century. Recent research indicates that heredity may be largely responsible for the degeneration as well as herniation of intervertebral discs. Since 1998, genetic influences have been confirmed by the identification of several genes forms associated with disc degeneration. These researches are paving the way for a better understanding of the biologic mechanisms. Now, many researchers unanimously agree that lumbar disc herniation appears to be similar to other complex diseases, whose etiology has both environmental and hereditary influence, each with a part of contribution and relative risk. Then addressing the etiological of lumbar disc herniation, it is important to integrate heredity with the environment factors. For the purpose of this review, we have limited our discussion to several susceptibility genes associated with disc degeneration.

  4. Accretion disc viscosity: a limit on the anisotropy

    CERN Document Server

    Nixon, Chris

    2015-01-01

    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 timescales, 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 magneto-rotational instability. The constraints derived here are in agreement with analytical and numerical investigations into the nature of magneto-hydrodynamic disc turbulence, but at odds with some recent global simulations.

  5. Growth of eccentric modes in disc-planet interactions

    CERN Document Server

    Teyssandier, Jean

    2016-01-01

    We formulate a set of linear equations that describe the behaviour of small eccentricities in a protoplanetary system consisting of a gaseous disc and a planet. Eccentricity propagates through the disc by means of pressure and self-gravity, and is exchanged with the planet via secular interactions. Excitation and damping of eccentricity can occur through Lindblad and corotation resonances, as well as viscosity. We compute normal modes of the coupled disc-planet system in the case of short-period giant planets orbiting inside an inner cavity, possibly carved by the stellar magnetosphere. Three-dimensional effects allow for a mode to be trapped in the inner parts of the disc. This mode can easily grow within the disc's lifetime. An eccentric mode dominated by the planet can also grow, although less rapidly. We compute the structure and growth rates of these modes and their dependence on the assumed properties of the disc.

  6. Dynamical stability and evolution of the discs of Sc galaxies

    CERN Document Server

    Fuchs, B

    1997-01-01

    We examine the local stability of galactic discs against axisymmetric density perturbations with special attention to the different dynamics of the stellar and gaseous components. In particular the discs of the Milky Way and of NGC 6946 are studied. The Milky Way is shown to be stable, whereas the inner parts of NGC 6946, a typical Sc galaxy from the Kennicutt (1989) sample, are dynamically unstable. The ensuing dynamical evolution of the composite disc is studied by numerical simulations. The evolution is so fierce that the stellar disc heats up dynamically on a short time scale to such a degree, which seems to contradict the morphological appearance of the galaxy. The star formation rate required to cool the disc dynamically is estimated. Even if the star formation rate in NGC 6946 is at present high enough to meet this requirement, it is argued that the discs of Sc galaxies cannot sustain such a high star formation rate for longer periods.

  7. Effects of investigations into vibrating disc use for rock fracturing

    Energy Technology Data Exchange (ETDEWEB)

    Krauze, K.; Pawlik, J.; Pawlik, K.

    1987-06-01

    Evaluates results of laboratory investigations into feasibility of mine drivage by heading machines with vibrating discs for rock cutting. Each cutting head was equipped with 2 discs. Discs with a diameter of 200 mm, 50 mm thick and with a wedge angle of 90 degrees were used for cutting three types of rocks (2 types of sandstones with a compression strength exceeding 80 MPa). Amplitude of disc vibrations ranged from 4 to 8 mm, frequency from 12 to 20 Hz. Investigations showed vibrating discs to be an efficient tool for cutting rocks with a high compression strength. Cutting disc wear was extremely low in contrast to wear of conventional picks of the NK-4 type (which after cutting a 0.3 m long rock section were removed due to wear). Cutting energy depended on vibration frequency and amplitude. 5 refs.

  8. Disc loss and renewal in A0535+26

    OpenAIRE

    Haigh, N. J.; Coe, M. J.; Steele, I. A.; Fabregat, J.

    1999-01-01

    This paper presents observations of the Be/X-ray binary system A0535+26 revealing the first observed loss of its circumstellar disc, demonstrated by the loss of its JHK infrared excess and optical/IR line emission. However optical/IR spectroscopy reveals the formation of a new inner disc with significant density and emission strength at small radii; the disc has proven to be stable over 5 months in this intermediate state.

  9. Thoracic spine disc-related abnormalities: longitudinal MR imaging assessment

    Energy Technology Data Exchange (ETDEWEB)

    Girard, Charles J.; Schweitzer, Mark E.; Morrison, William B.; Parellada, Joan A. [TJUH Radiology, Philadelphia, Pennsylvania (United States); Carrino, J.A. [Department of Radiology ASB-1, Harvard Medical School, Brigham and Women' s Hospital, L1, Room 002B, 75 Francis Street, MA 02115, Boston (United States)

    2004-04-01

    To describe and characterize the temporal changes in disc-related disorders of the thoracic spine using MR imaging. A retrospective longitudinal cohort study was carried out of 40 patients with two sequential thoracic spine MR images at variable intervals. The images were assessed for baseline presence of, new incidence of and changes in disc herniation, degenerative disc disease, endplate marrow signal alteration and Schmorl nodes. The range of follow-up was 4-149 weeks. Baseline presence was: disc herniation, 10% (49/480); degenerative disc disease, 14% (66/480); endplate marrow signal alteration, 2.3% (11/480); Schmorl nodes 9.6% (46/480). Most pre-existing lesions tended to remain unchanged. Herniations showed the most change, tending to improve in 27%. New incidence was: disc herniation, 1.5% (7/480), degenerative disc disease, 2% (10/480); endplate marrow signal alteration, 1.6% (8/480); Schmorl nodes, 2.1% (10/480). Disc degeneration was first visible at an 11-week interval and once established almost never changed over many weeks to months. Endplate signal alterations (Modic changes) were uncommon. Schmorl nodes show no change from baseline for up to 2 1/2 years. All findings predominated in the lower intervertebral levels from T6 to T10. The most prevalent thoracic spine disc-related findings are degeneration and herniation. Disc herniations predominate in the lower segments and are a dynamic phenomenon. Disc degeneration can be rapidly evolving but tends to remain unchanged after occurrence. Endplate marrow signal changes were an uncommon manifestation of thoracic disc disease. Schmorl nodes showed the least change over time. (orig.)

  10. Temporomandibular joint loads in subjects with and without disc displacement.

    Science.gov (United States)

    Iwasaki, Laura R; Crosby, Michael J; Gonzalez, Yoly; McCall, Willard D; Marx, David B; Ohrbach, Richard; Nickel, Jeffrey C

    2009-01-01

    The likelihood of development of degenerative joint disease (DJD) of the temporomandibular joint (TMJ) is related to the integrity of the TMJ disc. Predilection for mechanical failure of the TMJ disc may reflect inter-individual differences in TMJ loads. Nine females and eight males in each of normal TMJ disc position and bilateral disc displacement diagnostic groups consented to participate in our study. Disc position was determined by bilateral magnetic resonance images of the joints. Three-dimensional (3D) anatomical geometry of each subject was used in a validated computer-assisted numerical model to calculate ipsilateral and contralateral TMJ loads for a range of biting positions (incisor, canine, molar) and angles (1-13). Each TMJ load was a resultant vector at the anterosuperi or-most mediolateral midpoint the condyle and characterized in terms of magnitude and 3D orientation. Analysis of variance (ANOVA) was used to test for effects of biting position and angle on TMJ loads. Mean TMJ loads in subjects with disc displacement were 9.5-69% higher than in subjects with normal disc position. During canine biting, TMJ loads in subjects with disc displacement were 43% (ipsilateral condyle, p=0.029) and 49% (contralateral condyle, p=0.015) higher on average than in subjects with normal disc position. Biting angle effects showed that laterally directed forces on the dentition produced ipsilateral joint loads, which on average were 69% higher (p=0.002) compared to individuals with normal TMJ disc position. The data reported here describe large differences in TMJ loads between individuals with disc displacement and normal disc position. The results support future investigations of inter-individual differences in joint mechanics as a variable in the development of DJD of the TMJ.

  11. Orbital evolution of eccentric planets in radiative discs

    Science.gov (United States)

    Bitsch, B.; Kley, W.

    2010-11-01

    Context. With an average eccentricity of about 0.29, the eccentricity distribution of extrasolar planets is markedly different from the solar system. Among other scenarios considered, it has been proposed that eccentricity may grow through planet-disc interaction. Recently, it has been noticed that the thermodynamical state of the disc can significantly influence the migration properties of growing protoplanets. However, the evolution of planetary eccentricity in radiative discs has not been considered yet. Aims: In this paper we study the evolution of planets on eccentric orbits that are embedded in a three-dimensional viscous disc and analyse the disc's effect on the orbital evolution of the planet. Methods: We use the three-dimensional hydrodynamical code NIRVANA that includes full tensor viscosity and implicit radiation transport in the flux-limited diffusion approximation. The code uses the FARGO-algorithm to speed up the simulations. First we measure the torque and power exerted on the planet by the disc for fixed orbits, and then we let the planet start with initial eccentricity and evolve it in the disc. Results: For locally isothermal discs we confirm previous results and find eccentricity damping and inward migration for planetary cores. For low eccentricity (e ⪉ 2 H/r) the damping is exponential, while for higher e it follows dot{e} ∝ e-2. In the case of radiative discs, the planets experience an inward migration as long as its eccentricity lies above a certain threshold. After the damping of eccentricity cores with masses below 33 MEarth begin to migrate outward in radiative discs, while higher mass cores always migrate inward. For all planetary masses studied (up to 200 MEarth) we find eccentricity damping. Conclusions: In viscous discs the orbital eccentricity of embedded planets is damped during the evolution independent of the mass. Hence, planet-disc interaction does not seem to be a viable mechanism to explain the observed high eccentricity of

  12. Temporomandibular joint loads in subjects with and without disc displacement

    Directory of Open Access Journals (Sweden)

    Laura Rei Iwasaki

    2009-12-01

    Full Text Available The likelihood of development of degenerative joint disease (DJD of the temporomandibular joint (TMJ is related to the integrity of the TMJ disc. Predilection for mechanical failure of the TMJ disc may reflect inter-individual differences in TMJ loads. Nine females and eight males in each of normal TMJ disc position and bilateral disc displacement diagnostic groups consented to participate in our study. Disc position was determined by bilateral magnetic resonance images of the joints. Three-dimensional (3D anatomical geometry of each subject was used in a validated computer-assisted numerical model to calculate ipsilateral and contralateral TMJ loads for a range of biting positions (incisor, canine, molar and angles (1-13. Each TMJ load was a resultant vector at the anterosuperior-most mediolateral midpoint on the condyle and characterized in terms of magnitude and 3D orientation. Analysis of variance (ANOVA was used to test for effects of biting position and angle on TMJ loads. Mean TMJ loads in subjects with disc displacement were 9.5-69% higher than in subjects with normal disc position. During canine biting, TMJ loads in subjects with disc displacement were 43% (ipsilateral condyle, p=0.029 and 49% (contralateral condyle, p=0.015 higher on average than in subjects with normal disc position. Biting angle effects showed that laterally directed forces on the dentition produced ipsilateral joint loads, which on average were 69% higher (p=0.002 compared to individuals with normal TMJ disc position. The data reported here describe large differences in TMJ loads between individuals with disc displacement and normal disc position. The results support future investigations of inter-individual differences in joint mechanics as a variable in the development of DJD of the TMJ.

  13. Clinical Evaluation of Disc Battery Ingestion in Children

    OpenAIRE

    Mirshemirani, Alireza; Khaleghnejad-tabari, Ahmad; Kouranloo, Jaefar; Sadeghian, Naser; Rouzrokh, Mohsen; Roshanzamir, Fatolah; Razavi, Sajad; Sayary, Ali Akbar; Imanzadeh, Farid

    2012-01-01

    BACKGROUND The purpose of this study was to evaluate the characteristics, management, and outcomes of disc battery ingestion in children. METHODS We reviewed the medical records of children admitted to Mofid Children’s Hospital due to disc battery ingestion from January 2006 to January 2010. Clear history, clinical symptoms and results of imaging studies revealed diagnosis of disc battery ingestion in suspected patients. The clinical data reviewed included age, gender, clinical manifestation,...

  14. A Review of a Study on Disc Brake Noise

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    With the development of the automotive industry, disc brake noise has become an issue of growing concern to the automotive industry and customers. In this paper, the types of disc brake noise have been discussed. Ajter that, the theories and models that have been proposed as an explanation of brake squeal are reviewed. On the basis of these theories and models, some example simulations of disc brake squeal which use the Finite Element method and mathematical model have been introduced.

  15. Unsteady Heat Transfer From a Non Isothermal Rotating Disc

    Directory of Open Access Journals (Sweden)

    Bal Krishan

    1967-01-01

    Full Text Available An analytic solution of the energy equation is obtained for a non-isothermal disc rotating in an incompressible fluid at rest neglecting the viscous dissipation. Initially the disc and the fluid are at a common temperature. Without altering the velocity, the disc temperature is then changed and maintained at temperature varying according to the power law of radial distance. Expressions for temperature distribution in the fluid for large and small times have been evaluated.

  16. Audiovisual Bounce-Inducing Effect: Attention Alone Does Not Explain Why the Discs Are Bouncing

    Science.gov (United States)

    Grassi, Massimo; Casco, Clara

    2009-01-01

    Two discs moving from opposite points in space, overlapping and stopping at the other disc's starting point, can be seen as either bouncing or streaming through each other. With silent displays, observers report the discs as streaming, whereas if a sound is played when the discs touch each other, observers report the discs as bouncing. The origin…

  17. Self-gravitating disc candidates around massive young stars

    Science.gov (United States)

    Forgan, D. H.; Ilee, J. D.; Cyganowski, C. J.; Brogan, C. L.; Hunter, T. R.

    2016-11-01

    There have been several recent detections of candidate Keplerian discs around massive young protostars. Given the relatively large disc-to-star mass ratios in these systems, and their young ages, it is worth investigating their propensity to becoming self-gravitating. To this end, we compute self-consistent, semi-analytic models of putative self-gravitating discs for five candidate disc systems. Our aim is not to fit exactly the observations, but to demonstrate that the expected dust continuum emission from marginally unstable self-gravitating discs can be quite weak, due to high optical depth at the mid-plane even at millimetre wavelengths. In the best cases, the models produce `observable' disc masses within a factor of self-gravitating disc model compares well with observations. If these discs are self-gravitating, they satisfy the conditions for disc fragmentation in their outer regions. These systems may hence have as-yet-unresolved low-mass stellar companions, and are thus promising targets for future high angular resolution observations.

  18. The effect of radiative feedback on disc fragmentation

    Science.gov (United States)

    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.

  19. A disc-type magneto-rheologic fluid damper

    Institute of Scientific and Technical Information of China (English)

    祝长生

    2003-01-01

    A disc-type magneto-rheological fluid damper operating in shear mode is proposed in this paper, which is based on the special characteristics of the magneto-rheological (MR) fluid with rapid, reversible and dramatic change in its rheological properties by the application of an external magnetic field. The magnetic field of the disc-type MR fluid damper is analysed by the finite element method; the controllability of the disc-type MR fluid damper on the dynamic behaviour of a rotor system; and the effectiveness of the disc-type MR fluid damper in controlling the vibration of a rotor system, are studied in a flexible rotor system with an over-hung disc. It is shown that the magnetic flux density of the disc-type MR fluid damper in the working areas can significantly change with the applied current in the coil; and that the dynamic behavior of the disc-type MR fluid damper can be varied by the application of an external magnetic field produced by a low voltage electromagnetic coil. The disc-type MR fluid damper can significantly change the dynamic characteristics of a rotor system, provided that the location of the disk-type MR fluid damper is carefully chosen. The disc-type MR fluid damper is a new actuator with good dynamic characteristics for rotating machinery.

  20. Pathophysiological basis of lumbar disc degeneration: imaging analysis.

    Science.gov (United States)

    Ostrum, B J; Romy, M; Swartz, J D

    1993-12-01

    This article provides a brief synopsis of the pathoanatomic basis of disc degeneration. An attempt is made to correlate CT, MR and CT discographic findings. The T2-weighted sagittal images are the most sensitive for evaluating disc degeneration. The contour changes on axial CT and MR scans are sensitive for abnormalities but not always specific. The CT discogram adds information unavailable by other imaging methods pertaining to the internal architecture of the disc. It additionally defines focal nuclear herniations and also is helpful in evaluating the stage of disc degeneration.

  1. Notochord Cells in Intervertebral Disc Development and Degeneration

    Directory of Open Access Journals (Sweden)

    Matthew R. McCann

    2016-01-01

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

  2. The hunt for the Milky Way's accreted disc

    CERN Document Server

    Ruchti, Gregory R; Feltzing, Sofia; Pipino, Antonio; Bensby, Thomas

    2014-01-01

    The Milky Way is expected to host an accreted disc of stars and dark matter. This forms as massive >1:10 mergers are preferentially dragged towards the disc plane by dynamical friction and then tidally shredded. The accreted disc likely contributes only a tiny fraction of the Milky Way's thin and thick stellar disc. However, it is interesting because: (i) its associated `dark disc' has important implications for experiments hoping to detect a dark matter particle in the laboratory; and (ii) the presence or absence of such a disc constrains the merger history of our Galaxy. In this work, we develop a chemo-dynamical template to hunt for the accreted disc. We apply our template to the high-resolution spectroscopic sample from Ruchti et al. (2011), finding at present no evidence for accreted stars. Our results are consistent with a quiescent Milky Way with no >1:10 mergers since the disc formed and a correspondingly light `dark disc'. However, we caution that while our method can robustly identify accreted stars...

  3. MECHANICAL DESIGN CRITERIA FOR INTERVERTEBRAL DISC TISSUE ENGINEERING

    Science.gov (United States)

    Nerurkar, Nandan L.; Elliott, Dawn M.; Mauck, Robert L.

    2009-01-01

    Due to the inability of current clinical practices to restore function to degenerated intervertebral discs, the arena of disc tissue engineering has received substantial attention in recent years. Despite tremendous growth and progress in this field, translation to clinical implementation has been hindered by a lack of well-defined functional benchmarks. Because successful replacement of the disc is contingent upon replication of some or all of its complex mechanical behaviour, it is critically important that disc mechanics be well characterized in order to establish discrete functional goals for tissue engineering. In this review, the key functional signatures of the intervertebral disc are discussed and used to propose a series of native tissue benchmarks to guide the development of engineered replacement tissues. These benchmarks include measures of mechanical function under tensile, compressive and shear deformations for the disc and its substructures. In some cases, important functional measures are identified that have yet to be measured in the native tissue. Ultimately, native tissue benchmark values are compared to measurements that have been made on engineered disc tissues, identifying measures where functional equivalence was achieved, and others where there remain opportunities for advancement. Several excellent reviews exist regarding disc composition and structure, as well as recent tissue engineering strategies; therefore this review will remain focused on the functional aspects of disc tissue engineering. PMID:20080239

  4. Generating large misalignments in gapped and binary discs

    Science.gov (United States)

    Owen, James E.; Lai, Dong

    2017-08-01

    Many protostellar gapped and binary discs show misalignments between their inner and outer discs; in some cases, ˜70° misalignments have been observed. Here, we show that these misalignments can be generated through a secular resonance between the nodal precession of the inner disc and the precession of the gap-opening (stellar or massive planetary) companion. An evolving protostellar system may naturally cross this resonance during its lifetime due to disc dissipation and/or companion migration. If resonance crossing occurs on the right time-scale, of the order of a few million years, characteristic for young protostellar systems, the inner and outer discs can become highly misaligned, with misalignments ≳ 60° typical. When the primary star has a mass of order a solar mass, generating a significant misalignment typically requires the companion to have a mass of ˜0.01-0.1 M⊙ and an orbital separation of tens of astronomical units. The recently observed companion in the cavity of the gapped, highly misaligned system HD 142527 satisfies these requirements, indicating that a previous resonance crossing event misaligned the inner and outer discs. Our scenario for HD 142527's misaligned discs predicts that the companion's orbital plane is aligned with the outer disc's; this prediction should be testable with future observations as the companion's orbit is mapped out. Misalignments observed in several other gapped disc systems could be generated by the same secular resonance mechanism.

  5. Self-gravitating disc candidates around massive young stars

    CERN Document Server

    Forgan, D H; Cyganowski, C J; Brogan, C L; Hunter, T R

    2016-01-01

    There have been several recent detections of candidate Keplerian discs around massive young protostars. Given the relatively large disc-to-star mass ratios in these systems, and their young ages, it is worth investigating their propensity to becoming self-gravitating. To this end, we compute self-consistent, semi-analytic models of putative self-gravitating discs for five candidate disc systems. Our aim is not to fit exactly the observations, but to demonstrate that the expected dust continuum emission from marginally unstable self-gravitating discs can be quite weak, due to high optical depth at the midplane even at millimetre wavelengths. In the best cases, the models produce "observable" disc masses within a factor of <1.5 of those observed, with midplane dust temperatures comparable to measured temperatures from molecular line emission. We find in two cases that a self-gravitating disc model compares well with observations. If these discs are self-gravitating, they satisfy the conditions for disc fragm...

  6. A computational study of intervertebral disc degeneration in relation to changes in regional tissue composition and disc nutrition

    OpenAIRE

    2015-01-01

    Up to 85% of the world population suffers from low back pain, a clinical condition often related to the intervertebral disc (IVD) degeneration (DD). Altered disc cell nutrition affects cell viability and can generate catabolic cascades that degrade the extracellular matrix (ECM). Also, a major degenerative biochemical change in the disc is the proteoglycan (PG) loss, which affects the osmotic pressure and hydration that is critical for cell nutrition. However, the relationship between biochem...

  7. Structure and kinematics of edge-on galaxy discs - IV. The kinematics of the stellar discs

    NARCIS (Netherlands)

    Kregel, M; van der Kruit, PC

    2005-01-01

    The stellar disc kinematics in a sample of 15 intermediate- to late-type edge-on spiral galaxies are studied using a dynamical modelling technique. The sample covers a substantial range in maximum rotation velocity and deprojected face-on surface brightness and contains seven spirals with either a b

  8. Analysis of crucial molecules involved in herniated discs and degenerative disc disease

    Directory of Open Access Journals (Sweden)

    Zhigang Qu

    2013-01-01

    Full Text Available OBJECTIVES: Herniated discs and degenerative disc disease are major health problems worldwide. However, their pathogenesis remains obscure. This study aimed to explore the molecular mechanisms of these ailments and to identify underlying therapeutic targets. MATERIAL AND METHODS: Using the GSE23130 microarray datasets downloaded from the Gene Expression Omnibus database, differentially co-expressed genes and links were identified using the differentially co-expressed gene and link method with a false discovery rate ,0.25 as a significant threshold. Subsequently, the underlying molecular mechanisms of the differential co-expression of these genes were investigated using Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. In addition, the transcriptional regulatory relationship was also investigated. RESULTS: Through the analysis of the gene expression profiles of different specimens from patients with these diseases, 539 differentially co-expressed genes were identified for these ailments. The ten most significant signaling pathways involving the differentially co-expressed genes were identified by enrichment analysis. Among these pathways, apoptosis and extracellular matrix-receptor interaction pathways have been reported to be related to these diseases. A total of 62 pairs of regulatory relationships between transcription factors and their target genes were identified as critical for the pathogenesis of these diseases. CONCLUSION: The results of our study will help to identify the mechanisms responsible for herniated discs and degenerative disc disease and provides a theoretical basis for further therapeutic study.

  9. Disc and condylar head position in the temporomandibular joint with and without disc displacement.

    Science.gov (United States)

    Badel, Tomislav; Pavicin, Ivana Savić; Jakovac, Marko; Kern, Josipa; Zadravec, Dijana

    2013-09-01

    The purpose of this study was to evaluate the difference between disc and condyle position between temporomandibular joints (TMJs) without disc displacement (DD) in asymptomatic volunteers, and patients who have DD in contralateral joints, respectively unilateral DD. Secondly, there were two TMJ groups which consisted of measurements from patients' symptomatic DD and volunteers with asymptomatic DD. The study included 79 TMJs of 40 patients with unilateral DD. In the group of 25 asymptomatic volunteers, 20 volunteers were without DD bilaterally (40 joints), while five had DD in at least one TMJ. All subjects were examined clinically and DD was confirmed by magnetic resonance imaging. Left and right TMJs were analysed independently for each participant based on their DD status (symptomatic, asymptomatic, and without DD). All asymptomatic TMJs did not have any clinical signs of TMJ functional abnormalities. There was a significant statistical difference between disc position among TMJs without DD in asymptomatic volunteers and TMJs without DD in patients (p = 0.016). Moreover, no significant differences were found between condyle position in the same groups of joints (p = 0.706). There were no significant differences in the DD position (p = 0.918) or condyle position (p = 0.453) between the group with asymptomatic volunteers' joints and the group with symptomatic patients' joints. There was a significant difference between patient and volunteers' joints without DD: the disc was positioned more anteriorly in patients' joints without DD than in joints of asymptomatic volunteers without DD.

  10. Likelihood inference for unions of interacting discs

    DEFF Research Database (Denmark)

    Møller, Jesper; Helisova, K.

    2010-01-01

    with respect to a given marked Poisson model (i.e. a Boolean model). We show how edge effects and other complications can be handled by considering a certain conditional likelihood. Our methodology is illustrated by analysing Peter Diggle's heather data set, where we discuss the results of simulation......This is probably the first paper which discusses likelihood inference for a random set using a germ-grain model, where the individual grains are unobservable, edge effects occur and other complications appear. We consider the case where the grains form a disc process modelled by a marked point......-based maximum likelihood inference and the effect of specifying different reference Poisson models....

  11. Percutaneous treatment of lumbar disc herniation

    Energy Technology Data Exchange (ETDEWEB)

    Leonardi, M.; Resta, F.; Bettinelli, A. [Ospedale Maggiore di Milano (Italy); Lavaroni, A.; Fabris, G. [Ospedale Civile di Udine (Italy); Abelli, F. [Fondazione Clinica del Lavorno, Pavia (Italy)

    1994-12-31

    918 patients were subjected to percutaneous treatment of lumbar herniated disc. 733 of these were treated through enzymatic nucleolysis with chymopapain, for a total 883 levels. Chemonucleolysis was carried out on 733 patients (79.8%). Automated discectomy has been carried out in 185 cases (20.1%). Chemonucleolysis has led to the resolution of the symptoms in a high percentage of cases (82.2%). Nucleotomy has proved to be an effective method in 74.6% of cases. (author). 7 refs, 6 figs, 1 tab.

  12. Slim accretion discs with different viscosity prescriptions

    Energy Technology Data Exchange (ETDEWEB)

    Szuszkiewicz, E. (Max-Planck-Institut fuer Physik und Astrophysik, Garching (Germany, F.R.). Inst. fuer Astrophysik)

    1990-05-15

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

  13. An Analysis of Burst Disc Pressure Instability

    Energy Technology Data Exchange (ETDEWEB)

    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

  14. [LOCATION CHANGE OF ROTATION CENTER AFTER SINGLE SEGMENTAL CERVICAL DISC REPLACEMENT WITH ProDisc-C].

    Science.gov (United States)

    Lou, Jigang; Liu, Hao; Rong, Xin; Gong, Quan; Song, Yueming; Li, Tao

    2015-01-01

    To evaluate the effectiveness of the single segmental cervical disc replacement with ProDisc-C, and to explore the location change of the flexion/extension center of rotation (COR) of the target level as well as its clinical significance. Between June 2010 and February 2012, 23 patients underwent single segmental cervical disc replacement with ProDisc-C, and the clinical data were retrospectively analyzed. Of 23 patients, 9 were male, and 14 were female with the age range from 27 to 65 years (mean, 45 years), and the disease duration ranged from 10 to 84 months (mean, 25 months). There were 15 patients with radiculopathy, 5 patients with myelopathy, and 3 patients with mixed cervical spondylosis. The involved segments were C4,5 in 5 cases, C5,6 in 14 cases, and C6,7 in 4 cases. Japanese Orthopaedic Association (JOA) score and neck disability index (NDI) were adopted to evaluate the effectiveness. Preoperative and Postoperative radiographic parameters, such as cervical overall range of motion (ROM), target segmental ROM, the adjacent segmental ROM, and intervertebral height were compared. Besides, the location changes of the COR of the target level were further analyzed by the alteration of its coordinates (COR-X, COR-Y), and the relationships between the location changes of the COR and the effectiveness or the radiographic results were analyzed. All the operations were completed successfully; 1 case had hoarseness after operation, which disappeared at 3 months after operation. All cases were followed up 18.3 months on average (range, 6-36 months). There was no device migration, loosening, subsidence, or fracture at last follow-up. The JOA score increased significantly and the NDI score decreased significantly at last follow-up when compared with preoperative scores (P 0.05); while the intervertebral height and the COR-X increased significantly (P 0.05). According to whether the difference of the COR-X between pre- and post-operation was less than the average value

  15. Evolution of accretion disc flow in cataclysmic variables. 3. Outburst properties of constant and uniform-. cap alpha. model discs

    Energy Technology Data Exchange (ETDEWEB)

    Lin, D.N.C.; Faulkner, J. (Lick Observatory, Santa Cruz, CA (USA); California Univ., Santa Cruz (USA). Board of Studies in Astronomy and Astrophysics); Papaloizou, J. (Queen Mary Coll., London (UK). Dept. of Applied Mathematics)

    1985-01-01

    The investigation of accretion disc models relevant to cataclysmic-variable systems is continued. This paper examines the stability and evolution of some simple accretion disc models in which the viscosity is prescribed by an ad hoc uniform-..cap alpha.. model. It is primarily concerned with systems in which the mass-input rate from the secondary to the disc around the primary is assumed to be constant. However, initial calculations with variable mass-input rates are also performed. The time-dependent visual magnitude light-curves are constructed for cataclysmic binaries with a range of disc size, primary mass, mass-input rate, and magnitude of viscosity.

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

    Science.gov (United States)

    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 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.

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

    Science.gov (United States)

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

    2016-04-01

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

  18. File list: Pol.Lar.05.AllAg.Dorsal_mesothoracic_disc [Chip-atlas[Archive

    Lifescience Database Archive (English)

    Full Text Available Pol.Lar.05.AllAg.Dorsal_mesothoracic_disc dm3 RNA polymerase Larvae Dorsal mesothoracic disc...iosciencedbc.jp/kyushu-u/dm3/assembled/Pol.Lar.05.AllAg.Dorsal_mesothoracic_disc.bed ...

  19. File list: Pol.Lar.20.AllAg.Dorsal_mesothoracic_disc [Chip-atlas[Archive

    Lifescience Database Archive (English)

    Full Text Available Pol.Lar.20.AllAg.Dorsal_mesothoracic_disc dm3 RNA polymerase Larvae Dorsal mesothoracic disc...iosciencedbc.jp/kyushu-u/dm3/assembled/Pol.Lar.20.AllAg.Dorsal_mesothoracic_disc.bed ...

  20. File list: Pol.Lar.10.AllAg.Dorsal_mesothoracic_disc [Chip-atlas[Archive

    Lifescience Database Archive (English)

    Full Text Available Pol.Lar.10.AllAg.Dorsal_mesothoracic_disc dm3 RNA polymerase Larvae Dorsal mesothoracic disc...iosciencedbc.jp/kyushu-u/dm3/assembled/Pol.Lar.10.AllAg.Dorsal_mesothoracic_disc.bed ...

  1. File list: Pol.Lar.50.AllAg.Dorsal_mesothoracic_disc [Chip-atlas[Archive

    Lifescience Database Archive (English)

    Full Text Available Pol.Lar.50.AllAg.Dorsal_mesothoracic_disc dm3 RNA polymerase Larvae Dorsal mesothoracic disc...iosciencedbc.jp/kyushu-u/dm3/assembled/Pol.Lar.50.AllAg.Dorsal_mesothoracic_disc.bed ...

  2. MHD Disc Winds and Linewidth Distributions

    CERN Document Server

    Chajet, Laura S

    2013-01-01

    We study AGN emission line profiles combining an improved version of the accretion disc-wind model of Murray & Chiang with the magneto-hydrodynamic model of Emmering et al. We show how the shape, broadening and shift of the C IV line depend not only on the viewing angle to the object but also on the wind launching angle, especially for small launching angles. We have compared the dispersions in our model C IV linewidth distributions to observational upper limit on that dispersion, considering both smooth and clumpy torus models. As the torus half-opening angle (measured from the polar axis) increases above about 18? degrees, increasingly larger wind launching angles are required to match the observational constraints. Above a half-opening angle of about 47? degrees, no wind launch angle (within the maximum allowed by the MHD solutions) can match the observations. Considering a model that replaces the torus by a warped disc yields the same constraints obtained with the two other models.

  3. Decimetre dust aggregates in protoplanetary discs

    CERN Document Server

    Teiser, Jens; 10.1051/0004-6361/200912027

    2011-01-01

    The growth of planetesimals is an essential step in planet formation. Decimetre-size dust agglomerates mark a transition point in this growth process. In laboratory experiments we simulated the formation, evolution, and properties of decimetre-scale dusty bodies in protoplanetary discs. Small sub-mm size dust aggregates consisting of micron-size SiO$_2$ particles randomly interacted with dust targets of varying initial conditions in a continuous sequence of independent collisions. Impact velocities were 7.7 m/s on average and in the range expected for collisions with decimetre bodies in protoplanetary discs. The targets all evolved by forming dust \\emph{crusts} with up to several cm thickness and a unique filling factor of 31% $\\pm$3%. A part of the projectiles sticks directly. In addition, some projectile fragments slowly return to the target by gravity. All initially porous parts of the surface, i.e. built from the slowly returning fragments, are compacted and firmly attached to the underlying dust layers b...

  4. Cluster dynamics largely shapes protoplanetary disc sizes

    CERN Document Server

    Vincke, Kirsten

    2016-01-01

    It is still on open question to what degree the cluster environment influences the sizes of protoplanetary discs surrounding young stars. Particularly so for the short-lived clusters typical for the solar neighbourhood in which the stellar density and therefore the influence of the cluster environment changes considerably over the first 10 Myr. In previous studies often the effect of the gas on the cluster dynamics has been neglected, this is remedied here. Using the code NBody6++ we study the stellar dynamics in different developmental phases - embedded, expulsion, expansion - including the gas and quantify the effect of fly-bys on the disc size. We concentrate on massive clusters ($M_{\\text{cl}} \\geq 10^3 - 6 \\cdot 10^4 M_{\\text{Sun}}$), which are representative for clusters like the Orion Nebula Cluster (ONC) or NGC 6611. We find that not only the stellar density but also the duration of the embedded phase matters. The densest clusters react fastest to the gas expulsion and drop quickly in density, here 98...

  5. Elasticplastic discs under plane stress conditions

    CERN Document Server

    Alexandrov, Sergey

    2015-01-01

    This Volume presents a unified approach to calculate the plane stress distribution of stress and strain in thin elastic/plastic discs subject to various loading conditions. There is a vast amount of literature on analytical and semi-analytical solutions for such discs obeying Tresca’s yield criterion and its associated flow rule. On the other hand, most of analytical and semi-analytical solutions for Mises yield criterion are based on the deformation theory of plasticity. A distinguished feature of the solutions given in the present volume is that the flow theory of plasticity and Mises yield criterion are adopted. The solutions are semi-analytical in the sense that numerical methods are only necessary to evaluate ordinary integrals and solve transcendental equations. The book shows that under certain conditions solutions based on the deformation and flow theories of plasticity coincide. All the solutions are illustrated with numerical examples. The goal of the book is to provide the reader with a vision an...

  6. Metallurgical modelling of superalloy disc isothermal forgings

    Science.gov (United States)

    Evans, R. W.

    1988-08-01

    The metallurgical structure of superalloy aeroengine disc forgings is a complex function of the forging operation parameters and the post forging heat treatment. It is often desirable to obtain certain specific structures in parts of the disc which are, for instance, resistant to crack propagation and this has traditionally been accomplished by means of a series of production trials. This expensive and time consuming procedure can be considerably shortened if the development of microstructure during the forging can be accurately modelled by a suitable computer code. Described here is such a model and its use in the design of isothermal forged components. The model discribed is a fully thermally coupled viscoplasticity finite element algorithm. It treats nodal velocities as the basic unknowns and both the mesh geometry and the various metallurgical structural terms are updated by a single step Euler scheme. Facilities are available for ensuring that surface nodes follow die shapes after impingement, that flow is incompressible and that suitable surface friction forces are applied. Throughout the whole forging process (which may involve the re-meshing of severely distorted elements), the metallurgical history of elements is retained so that the effects of subsequent heat treatments can be assessed.

  7. Testing Hydrodynamics Schemes in Galaxy Disc Simulations

    CERN Document Server

    Few, C G; Pettitt, A; Konstandin, L

    2016-01-01

    We examine how three fundamentally different numerical hydrodynamics codes follow the evolution of an isothermal galactic disc with an external spiral potential. We compare an adaptive mesh refinement code (RAMSES), a smoothed particle hydrodynamics code (sphNG), and a volume-discretised meshless code (GIZMO). Using standard refinement criteria, we find that RAMSES produces a disc that is less vertically concentrated and does not reach such high densities as the sphNG or GIZMO runs. The gas surface density in the spiral arms increases at a lower rate for the RAMSES simulations compared to the other codes. There is also a greater degree of substructure in the sphNG and GIZMO runs and secondary spiral arms are more pronounced. By resolving the Jeans' length with a greater number of grid cells we achieve more similar results to the Lagrangian codes used in this study. Other alterations to the refinement scheme (adding extra levels of refinement and refining based on local density gradients) are less successful i...

  8. The comparative analysis of rocks’ resistance to forward-slanting disc cutters and traditionally installed disc cutters

    Institute of Scientific and Technical Information of China (English)

    Zhao-Huang Zhang; Sun Fei; Meng Liang

    2016-01-01

    At present, disc cutters of a full face rock tun-nel boring machine are mostly mounted in the traditional way. Practical use in engineering projects reveals that this installation method not only heavily affects the operation life of disc cutters, but also increases the energy consump-tion of a full face rock tunnel boring machine. To straighten out this issue, therefore, a rock-breaking model is devel-oped for disc cutters’ movement after the research on the rock breaking of forward-slanting disc cutters. Equations of its displacement are established based on the analysis of velocity vector of a disc cutter’s rock-breaking point. The functional relations then are brought forward between the displacement parameters of a rock-breaking point and its coordinate through the analysis of micro displacement of a rock-breaking point. Thus, the geometric equations of rock deformation are derived for the forward-slanting installation of disc cutters. With a linear relationship remaining between the acting force and its deformation either before or after the leap breaking, the constitutive relation of rock deformation can be expressed in the form of generalized Hooke law, hence the comparative analysis of the variation in the resistance of rock to the disc cutters mounted in the forward-slanting way with that in the traditional way. It is discovered that with the same penetration, strain of the rock in contact with forward-slanting disc cutters is apparently on the decline, in other words, the resistance of rock to disc cutters is reduced. Thus wear of disc cutters resulted from friction is lowered and energy consumption is correspondingly decreased. It will be useful for the development of installation and design theory of disc cutters, and significant for the breakthrough in the design of full face rock tunnel boring machine.

  9. The truncation of stellar discs : The magnetic hypothesis

    NARCIS (Netherlands)

    Battaner, E; Florido, E; Jimenez-Vicente, J

    2002-01-01

    We propose a hypothesis of the truncation of stellar discs based on the magnetic model of the rotation curve of spiral galaxies. Once the disc had formed and acquired its present structure, approximately, three balanced forces were acting on the initial gas: gravity and magnetic forces, inwards, and

  10. Orbital eccentricity as a probe of thick disc formation scenarios

    NARCIS (Netherlands)

    Sales, Laura V.; Helmi, Amina; Abadi, Mario G.; Brook, Chris B.; Gomez, Facundo A.; Roskar, Rok; Debattista, Victor P.; House, Elisa; Steinmetz, Matthias; Villalobos, Alvaro

    2009-01-01

    We study the orbital properties of stars in four (published) simulations of thick discs formed by (i) accretion from disrupted satellites, (ii) heating of a pre-existing thin disc by a minor merger, (iii) radial migration and (iv) gas-rich mergers. We find that the distribution of orbital eccentrici

  11. Dynamical and chemical evolution of the thin disc

    Science.gov (United States)

    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.

  12. A disc-type magneto-rheologic fluid damper

    Institute of Scientific and Technical Information of China (English)

    祝长生

    2003-01-01

    A disc-type magneto-rheological fluid damper operating in shear mode is proposed in this paper,which is based on the special characteristics of the magneto-rheological (MR) fluid with rapid, reversible and dramatic change in its rheological properties by the application of an external magnetic field. The magneticfield of the disc-type MR fluid damper is analysed by the finite element method ; the controllability of the disctype MR fluid damper on the dynamic behaviour of a rotor system ; and the effectiveness of the disc-type MR fluid damper in controlling the vibration of a rotor system, are studied in a flexible rotor system with an over-hung disc. It is shown that the magnetic flux density of the disc-type MR fluid damper in the working areas can significantly change with the applied current in the coil ; and that the dynamic behavior of the disc-type MR fluid damper can be varied by the application of an external magnetic field produced by a low voltage electromagnetic coil. The disc-type MR fluid damper can significantly change the dynamic characteristics of a rotor system, provided that the location of the disk-type MR fluid damper is carefully chosen. The disc-type MR fluid damper is a new actuator with good dynamic characteristics for rotating machinery.

  13. A study of Impinging Flow on a Rotating Disc

    Directory of Open Access Journals (Sweden)

    Horia DUMITRESCU

    2014-09-01

    Full Text Available This paper focuses on the behavior of the boundary-layer laminar flow produced by a large radius no-thickness disc which rotates inside an axial stream. Some early solutions are only known for the upstream flow field, but the details of the flow behind the disc are still obscure. A better understanding of the mechanisms and the properties of the shear layer close to disc is sought through the development of an analytic theory and then is completed by CFD computations. This article also shows that the basic flow on the leeward side of disc is mostly rotational-inviscid and only on in the neighborhood of the disc surface there is a viscous layer which rotates drawn by disc. The viscous layer containing a thin Ekman sublayer and a thicker essentially inviscid superlayer, governed by Taylor-Proudman theorem, can carry three possible actions: centrifugal (pumping mode, neutral mode and centripetal (suction mode. The action type depends on the relative importance of effects given by translation of the fluid (W and rotation of the disc (ΩR, defined by a rotating parameter (W/ΩR. The existence of such modes is connected to the amount of angular momentum transferred outside the Ekman sublayer. A CFD analysis was used to identify the vortex structure which is responsible for the angular momentum transfer from the rotating disc to an axial stream.

  14. Optimization of Valve Disc Using Orthogonal Array and Kriging Model

    Science.gov (United States)

    Song, Xueguan; Wang, Lin; Kang, Jungho; Kim, Seung Gyu; Jo, Young Jik; Park, Youngchul

    2008-10-01

    A butterfly valve is a type of flow control device, typically used to regulate a fluid flowing. Currently, FEA is often used to predict the safety in the design of valve disc. Also, the study about the affection of butterfly valve's disc to the valve flow characteristics by using CFD has been done by many researchers. Along with the development of computer technique, design and analysis of computer experiments has becoming more and more important in engineering design and optimization. Hereinto Kriging model is one popular analysis approach for the purpose of creating a cheap "meta-model" as a surrogate to a computationally expensive simulation model. In this paper, the numerical analysis considered the strength, pressure loss coefficient and weight of valve disc simultaneously is investigated to improve the shape of a traditional butterfly valve disc. Firstly, an initial model of butterfly valve is made to evaluate the performance of the valve disc by using CFD and FEM. Then several experiments with different variables combination of the valve disc are conducted by mean of orthogonal array. Finally, the Kriging model is used to find the optimum variables combination of valve disc based on the result of computer experiments. In addition, the optimum result is verified by FEA and CFD simulation again. The result shows that compared with traditional computer experiments, optimization by using Kriging model can improve the weight of the valve disc very effectively in a short time.

  15. Density waves in debris discs and galactic nuclei

    CERN Document Server

    Jalali, Mir Abbas

    2011-01-01

    We study the linear perturbations of collisionless near-Keplerian discs that have a ring-like structure. Such systems are models for debris discs around stars and the stellar discs surrounding supermassive black holes at the centres of galaxies. Using a finite-element method, we solve the linearized collisionless Boltzmann equation and Poisson's equation for a wide range of disc masses and rms orbital eccentricities to obtain the eigenfrequencies and shapes of normal modes. We find that these discs can support large-scale `slow' modes, in which the frequency is proportional to the disc mass. Slow modes are present for arbitrarily small disc mass so long as the self-gravity of the disc is the dominant source of apsidal precession. We find that slow modes are of two general types: parent modes and hybrid child modes, the latter arising from resonant interactions between parent modes and singular van Kampen modes. The most prominent slow modes have azimuthal wavenumbers $m=1$ and $m=2$. We illustrate how slow mo...

  16. Delivery systems for the treatment of degenerated intervertebral discs

    NARCIS (Netherlands)

    Blanquer, S.B.G.; Grijpma, D.W.; Poot, A.A.

    2015-01-01

    The intervertebral disc (IVD) is the most avascular and acellular tissue in the body and therefore prone to degeneration. During IVD degeneration, the balance between anabolic and catabolic processes in the disc is deregulated, amongst others leading to alteration of extracellular matrix production,

  17. Goddard Earth Science Data and Information Center (GES DISC)

    Science.gov (United States)

    Kempler, Steve

    2016-01-01

    The GES DIS is one of 12 NASA Earth science data centers. The GES DISC vision is to enable researchers and educators maximize knowledge of the Earth by engaging in understanding their goals, and by leading the advancement of remote sensing information services in response to satisfying their goals. This presentation will describe the GES DISC approach, successes, challenges, and best practices.

  18. Morphological Evolution of Disc Galaxies in Binary Systems

    CERN Document Server

    Chan, R

    2013-01-01

    We present the results of several numerical simulations of disc binary galaxies. It was performed detailed numerical N-body simulations of the dynamical interaction of two disc galaxies. The disc galaxies are embedded in spherical halos of dark matter and present central bulges. The dynamical evolution of the binary galaxy is analyzed in order to study the morphological evolution of the stellar distribution of the discs. The satellite galaxy is held on fixed, coplanar or polar discs, of eccentric ($e=0.1$, $e=0.4$ or $e=0.7$) orbits. Both galaxies have the same mass and size similar to the Milk Way. We have shown that the merge of two disc galaxy, depending on the initial conditions, can result in a disc or a lenticular galaxy, instead of an elliptical one. Besides, we have demonstrated that the time of merging increases linearly with the initial apocentric distance of the galaxies and decreases with the orbit's eccentricity. We also have shown that the tidal forces and the fusion of the discs can excite tran...

  19. 21 CFR 872.3970 - Interarticular disc prosthesis (interpositional implant).

    Science.gov (United States)

    2010-04-01

    ... implant). 872.3970 Section 872.3970 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3970 Interarticular disc prosthesis (interpositional implant). (a) Identification. An interarticular disc...

  20. On the development of an artificial intervertebral disc

    NARCIS (Netherlands)

    Eijkelkamp, Marcus Franciscus

    2002-01-01

    Degenerative disc disease is one of the causes of low back pain. There are two major surgical interventions: spinal fusion and implantation of an artificial intervertebral disc. Spinal fusion alters the biomechanics of the spine, which may lead to further degeneration of the surrounding tissues and

  1. Method for improved reading of a digital data disc

    DEFF Research Database (Denmark)

    2004-01-01

    Method for regulating the control signal for adjustment of the optical path between a data disc and a signal pick-up detector system in a data disc drive, where the control is regulated as a response to the deviation of the actual reading signals from expected reading signals, and wherein...

  2. Effect of chewing upon disc reduction in the temporomandibular joint.

    NARCIS (Netherlands)

    Kalaykova, S.I.; Lobbezoo, F.; Naeije, M.

    2011-01-01

    AIMS: To test whether an intensive chewing exercise influences the moment of disc reduction in subjects with or without reports of intermittent locking of the jaw. METHODS: This experimental study included 15 subjects with a reducing anteriorly displaced disc (ADD) and with symptoms of intermittent

  3. Spontaneous regression of lumbar herniated disc Case presentation

    Directory of Open Access Journals (Sweden)

    Chiriac A.

    2015-12-01

    Full Text Available Intervertebral disc herniation is a common disease that usually requires surgical intervention. However, in some cases, neurological symptoms may improve with conservative treatment. In this article, we present a case with spontaneous regression of extruded lumbar herniated disc correlated with clinical improvement and documented with follow up MRI studies.

  4. On the formation of planetary systems in photoevaporating transition discs

    Science.gov (United States)

    Terquem, Caroline

    2017-01-01

    In protoplanetary discs, planetary cores must be at least 0.1 M⊕ at 1 au for migration to be significant; this mass rises to 1 M⊕ at 5 au. Planet formation models indicate that these cores form on million year time-scales. We report here a study of the evolution of 0.1 and 1 M⊕ cores, migrating from about 2 and 5 au, respectively, in million year old photoevaporating discs. In such a disc, a gap opens up at around 2 au after a few million years. The inner region subsequently accrete on to the star on a smaller time-scale. We find that, typically, the smallest cores form systems of non-resonant planets beyond 0.5 au with masses up to about 1.5 M⊕. In low-mass discs, the same cores may evolve in situ. More massive cores form systems of a few Earth-mass planets. They migrate within the inner edge of the disc gap only in the most massive discs. Delivery of material to the inner parts of the disc ceases with opening of the gap. Interestingly, when the heavy cores do not migrate significantly, the type of systems that are produced resembles our Solar system. This study suggests that low-mm flux transition discs may not form systems of planets on short orbits but may instead harbour Earth-mass planets in the habitable zone.

  5. Laser Discs, Barcodes, and Books--a Great Combination.

    Science.gov (United States)

    Peto, Erica

    1996-01-01

    Describes the use of barcodes to link laser discs with books in school libraries. Highlights include use of a barcode reader as a remote control device as well as a scanner, guidelines for making laser disc books, and a sidebar that explains how to make barcodes and describes software. (LRW)

  6. Orbital eccentricity as a probe of thick disc formation scenarios

    NARCIS (Netherlands)

    Sales, Laura V.; Helmi, Amina; Abadi, Mario G.; Brook, Chris B.; Gomez, Facundo A.; Roskar, Rok; Debattista, Victor P.; House, Elisa; Steinmetz, Matthias; Villalobos, Alvaro

    2009-01-01

    We study the orbital properties of stars in four (published) simulations of thick discs formed by (i) accretion from disrupted satellites, (ii) heating of a pre-existing thin disc by a minor merger, (iii) radial migration and (iv) gas-rich mergers. We find that the distribution of orbital

  7. On the high frequency spectrum of a classical accretion disc

    CERN Document Server

    Balbus, Steven A

    2014-01-01

    We derive simple and explicit expressions for the high frequency spectrum of a classical accretion disc. Both stress-free and finite stress inner boundaries are considered. A classical accretion disc spectrum with a stress-free inner boundary departs from a Wien spectrum at large $\

  8. Twisted accretion discs. Pt. 3. Application to Epsilon Aurigae

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, S.

    1987-04-15

    Twisting and alignment in a steady-state circumbinary accretion disc is studied. It is then used to account for observed features in the scenario of Epsilon Aurigae as a triple. The alignment depends on viscosity in the disc, but it is always substantial and leads to a tilted slab-like profile when viewed edge-on.

  9. Energetic Argument for Bimodal Black Hole Accretion discs

    Institute of Scientific and Technical Information of China (English)

    林一清; 卢炬甫; 顾为民

    2002-01-01

    Based on simple energetic considerations, we show that two crucial ingredients of bimodal black hole accretiondiscs, namely the sonic point and the transition radius, can be determined from the disc constant parameters.Thus, we can further justify the model of bimodal discs containing thermal instability triggered transition.

  10. Small-scale inviscid accretion discs around black holes

    CERN Document Server

    Beloborodov, A M; Beloborodov, Andrei M.; Illarionov, Andrei F.

    2000-01-01

    Gas falling quasi-spherically onto a Schwarzschild black hole can form an inner thin accretion disc if its specific angular momentum, $l$, exceeds $\\lmin\\approx 0.75r_gc$, where $r_g$ is the Schwarzschild radius. The standard disc model assumes $l\\gg\\lmin$. We argue that in many black-hole sources the accretion flows can have $l\\simgt\\lmin$, and assess the mechanism of accretion in this regime. In a range $\\lmindisc forms in which gas overcomes the centrifugal barrier and spirals fast into the black hole without any help of horizontal viscous stresses. Such an ``inviscid'' disc, however, interacts inelastically with the infall feeding the disc, which leads to energy dissipation. This interaction determines the disc dynamics and luminosity. We find the radiative efficiency of this accretion regime to be comparable with the efficiency of the standard disc. The maximum radius of the fast inviscid disc is $r_{\\rm max}\\approx 2\\lcr^2/r_gc^2\\sim 14 r_g$, and the energy release peaks at...

  11. Q criterion for disc stability modified by external tidal field

    CERN Document Server

    Jog, Chanda J

    2013-01-01

    The standard Q criterion (with Q > 1) describes the local stability of a disc supported by rotation and random motion. Most astrophysical discs, however, are under the influence of an external gravitational field which can affect their stability. A typical example is a galactic disc embedded in a dark matter halo. Here we do a linear perturbation analysis for a disc in an external field, and obtain a generalized dispersion relation and a modified stability criterion. An external field has two effects on the disc dynamics: first, it contributes to the unperturbed rotational field, and second, it adds a tidal field term in the stability parameter. A typical disruptive tidal field results in a higher modified Q value and hence leads to a more stable disc. We apply these results to the Milky Way, and to a low surface brightness galaxy UGC 7321. We find that in each case the stellar disc by itself is barely stable and it is the dark matter halo that stabilizes the disc against local, axisymmetric gravitational ins...

  12. Spontaneous regression of lumbar herniated disc Case presentation

    OpenAIRE

    Chiriac A.; Ion Giorgiana; Faiyad Z.; Poeata I.

    2015-01-01

    Intervertebral disc herniation is a common disease that usually requires surgical intervention. However, in some cases, neurological symptoms may improve with conservative treatment. In this article, we present a case with spontaneous regression of extruded lumbar herniated disc correlated with clinical improvement and documented with follow up MRI studies.

  13. Reliability of MRI findings in candidates for lumbar disc prosthesis

    Energy Technology Data Exchange (ETDEWEB)

    Berg, Linda; Espeland, Ansgar [Haukeland University Hospital, Department of Radiology, Bergen (Norway); University of Bergen, Section for Radiology, Department of Surgical Sciences, Bergen (Norway); Neckelmann, Gesche [Haukeland University Hospital, Department of Radiology, Bergen (Norway); Gjertsen, Oeivind [Oslo University Hospital, Department of Neuroradiology, Oslo (Norway); Hellum, Christian [Oslo University Hospital, Department of Orthopaedics, Oslo (Norway); University of Oslo, Department of Orthopaedics, Oslo (Norway); Johnsen, Lars G. [University Hospital of Trondheim, National Centre for Diseases of the Spine, Trondheim (Norway); University Hospital of Trondheim, Orthopaedic Department, Trondheim (Norway); Eide, Geir E. [Haukeland University Hospital, Centre for Clinical Research, Bergen (Norway); University of Bergen, Department of Public Health and Primary Health Care, Bergen (Norway)

    2012-07-15

    Limited reliability data exist for localised magnetic resonance imaging (MRI) findings relevant to planning of treatment with lumbar disc prosthesis and later outcomes. We assessed the reliability of such findings in chronic low back pain patients who were accepted candidates for disc prosthesis. On pretreatment MRI of 170 patients (mean age 41 years; 88 women), three experienced radiologists independently rated Modic changes, disc findings and facet arthropathy at L3/L4, L4/L5 and L5/S1. Two radiologists rerated 126 examinations. For each MRI finding at each disc level, agreement was analysed using the kappa statistic and differences in prevalence across observers using a fixed effects model. All findings at L3/L4 and facet arthropathy at L5/S1 had a mean prevalence <10% across observers and were not further analysed, ensuring interpretable kappa values. Overall interobserver agreement was generally moderate or good (kappa 0.40-0.77) at L4-S1 for Modic changes, nucleus pulposus signal, disc height (subjective and measured), posterior high-intensity zone (HIZ) and disc contour, and fair (kappa 0.24) at L4/L5 for facet arthropathy. Posterior HIZ at L5/S1 and severely reduced subjective disc height at L4/L5 differed up to threefold in prevalence between observers (p < 0.0001). Intraobserver agreement was mostly good or very good (kappa 0.60-1.00). In candidates for disc prosthesis, mostly moderate interobserver agreement is expected for localised MRI findings. (orig.)

  14. Delivery systems for the treatment of degenerated intervertebral discs

    NARCIS (Netherlands)

    Blanquer, S. B. G.; Grijpma, D. W.; Poot, A. A.

    2015-01-01

    The intervertebral disc (ND) is the most avascular and acellular tissue in the body and therefore prone to degeneration. During IVD degeneration, the balance between anabolic and catabolic processes in the disc is deregulated, amongst others leading to alteration of extracellular matrix production,

  15. Method for improved reading of a digital data disc

    DEFF Research Database (Denmark)

    2004-01-01

    Method for regulating the control signal for adjustment of the optical path between a data disc and a signal pick-up detector system in a data disc drive, where the control is regulated as a response to the deviation of the actual reading signals from expected reading signals, and wherein...... the control signal is regulated in dependence the tendency of said deviation....

  16. Magnetic resonance imaging of disc space infection revisited: temporal changes

    Institute of Scientific and Technical Information of China (English)

    Duan Shaoyin; Xu Bingqiang; Gina Di Primio; Cheemun Lum; Mark E Schweitzer

    2014-01-01

    Background Magnetic resonance imaging (MRI) has advantages in showing pathologic changes of disc space infection,which is important in clinical treatment.The purpose of this study was to describe the MRI findings of disc space infections in relation to chronicity.Methods MRI of 60 patients from January 1,2002 to April 30,2012 in Ottawa Hospital were retrospectively evaluated by two radiologists blindly.All patients had histological confirmation,with 55 having microbiological confirmation as well.These patients were divided into acute (n=18),subacute (n=21) and chronic (n=21) based on histological findings.The following potential signs of MRI finding were assessed:marrow edema,endplate erosions,disk fluid and height change,paraspinal mass,epidural collection,facet fluid and enhancement in the marrow,disc,paraspinal mass,and epidural involvement.Statistical analysis consisted of t-or F-tests and chi-square test.Results In the 60 patients,83 infected discs (single disc in 45 patients,2-4 discs in 15 patients) were found,including 22 discs in the acute group,30 discs in the subacute group,and 31 discs in the chronic group.There was a significant difference in the extent of marrow edema between the acute,subacute and chronic groups (P <0.05),with a gradually increasing extent from acute to chronic.The extent of endplate erosions increased with chronicity,but was not statistically significant.There were significant differences in the disc fluid,epidural collection,and disc enhancement among the acute,subacute and chronic groups,as well as the facet fluid between acute and chronic groups (P <0.05).There were no significant differences in the present probability of disc height loss,paraspinal mass,and marrow enhancement among the three groups (P >0.05).Conclusions From acute to chronic infections,the extent of marrow edema and endplate erosions appeared to gradually increase.Epidural collections and facet fluid are most frequently found in the acute group,while disc

  17. Feasibility of transit photometry of nearby debris discs

    CERN Document Server

    Zeegers, S T; Kalas, P

    2014-01-01

    Dust in debris discs is constantly replenished by collisions between larger objects. In this paper, we investigate a method to detect these collisions. We generate models based on recent results on the Fomalhaut debris disc, where we simulate a background star transiting behind the disc, due to the proper motion of Fomalhaut. By simulating the expanding dust clouds caused by the collisions in the debris disc, we investigate whether it is possible to observe changes in the brightness of the background star. We conclude that in the case of the Fomalhaut debris disc, changes in the optical depth can be observed, with values of the optical depth ranging from $10^{-0.5}$ for the densest dust clouds to $10^{-8}$ for the most diffuse clouds with respect to the background optical depth of $\\sim1.2\\times10^{-3}$.

  18. [Displacement and tissue remodeling of temporomandibular joint disc].

    Science.gov (United States)

    Wang, M Q

    2017-03-09

    Sounding takes the highest prevalence of the signs of temporomandibular disorders (TMD). The well accepted theory of the mechanism for temporomandibular joint (TMJ) sounding is the internal derangement typically characterized by disc displacement. However, according to literature, there are approximately one third of asymptomatic joints in population had disc displacement, and, on the other hand, there are one fourth of TMJ sounding patients had not signs or very limited signs of disc displacement. Replacing the displaced disc to the normal position via methods like surgical operation did not achieve satisfactory long-term outcomes. In this review, we discuss and analyze the possible remodeling of the joint disc displacement diagnosed with imaging based on the anatomy and pathophysiology.

  19. Design of an Annular Disc Subject to Thermomechanical Loading

    Directory of Open Access Journals (Sweden)

    Sergei Alexandrov

    2012-01-01

    Full Text Available Two solutions to design a thin annular disc of variable thickness subject to thermomechanical loading are proposed. It is assumed that the thickness of the disc is everywhere sufficiently small for the stresses to be averaged through the thickness. The state of stress is plane. The initiation of plastic yielding is controlled by Mises yield criterion. The design criterion for one of the solutions proposed requires that the distribution of stresses is uniform over the entire disc. In this case there is a relation between optimal values of the loading parameters at the final stage. The specific shape of the disc corresponds to each pair of such parameters. The other solution is obtained under the additional requirement that the distribution of strains is uniform. This solution exists for the disc of constant thickness at specific values of the loading parameters.

  20. Planet-disc interaction on a freely moving mesh

    CERN Document Server

    Munoz, Diego J; Springel, Volker; Hernquist, Lars

    2014-01-01

    General-purpose, moving-mesh schemes for hydrodynamics have opened the possibility of combining the accuracy of grid-based numerical methods with the flexibility and automatic resolution adaptivity of particle-based methods. Due to their supersonic nature, Keplerian accretion discs are in principle a very attractive system for applying such freely moving mesh techniques. However, the high degree of symmetry of simple accretion disc models can be difficult to capture accurately by these methods, due to the generation of geometric grid noise and associated numerical diffusion, which is absent in polar grids. To explore these and other issues, in this work we study the idealized problem of two-dimensional planet-disc interaction with the moving-mesh code AREPO. We explore the hydrodynamic evolution of discs with planets through a series of numerical experiments that vary the planet mass, the disc viscosity and the mesh resolution, and compare the resulting surface density, vortensity field and tidal torque with ...

  1. Three-dimensional simulation of polytropic accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Molteni, D. (Palermo Univ. (Italy). Ist. di Fisica); Belvedere, G.; Lanzafame, G. (Catania Univ. (Italy). Ist. di Astronomia)

    1991-04-15

    We carried out three-dimensional simulations of the formation and evolution of accretion discs in close binary systems, using the Smoothed Particle Hydrodynamics method to solve the fluid dynamic equations. Although the runs presented here refer to an ideal gas with different polytropic indexes, and constitute the first stage of more physically complex forthcoming simulations, they nevertheless give some interesting results; the disc structure and dynamics are in agreement with standard models only for small {gamma}-values; as a consequence of the z-resolution is found that disc formation is inhibited for {gamma} {ge} 1.2, which means that some 2D simulations of polytropic discs are meaningless; the disc is slightly asymmetric in the x-y plane and its profile is irregular and pulsating at the outer boundary. (Author).

  2. Temperature Profile of Black Hole Accretion Disc with Magnetic Coupling

    Institute of Scientific and Technical Information of China (English)

    LEI Wei-Hua; WANG Ding-Xiong; XIAO Kan

    2002-01-01

    Two new mapping relations between the angular coordinate on the black hole (BH) horizon and radialcoordinate on the disc are given according to the requirement of general relativity and Maxwell's equations, and theeffects of magnetic coupling (MC) on temperature of accretion disc are investigated by comparing with pure accretion.It is shown that the MC effects on the temperature profile are related intimately to the BH spin, and the influenceon the peak value of disc temperature based on the modified mapping relations is not as great as that based on thelinear mapping.The peak value and the corresponding radius of peak value ring of disc temperature do not increasemonotonically as the increasing spin of BH, each containing a maximum for the fast-spinning BH. The value ranges ofthe bolometric luminosity and color temperature of the disc are both extended by the MC effects.

  3. Local and global dynamics of eccentric astrophysical discs

    CERN Document Server

    Ogilvie, Gordon I

    2014-01-01

    We formulate a local dynamical model of an eccentric disc in which the dominant motion consists of elliptical Keplerian orbits. The model is a generalization of the well known shearing sheet, and is suitable for both analytical and computational studies of the local dynamics of eccentric discs. It is spatially homogeneous in the horizontal dimensions but has a time-dependent geometry that oscillates at the orbital frequency. We show how certain averages of the stress tensor in the local model determine the large-scale evolution of the shape and mass distribution of the disc. The simplest solutions of the local model are laminar flows consisting of a (generally nonlinear) vertical oscillation of the disc. Eccentric discs lack vertical hydrostatic equilibrium because of the variation of the vertical gravitational acceleration around the eccentric orbit, and in some cases because of the divergence of the orbital velocity field associated with an eccentricity gradient. We discuss the properties of the laminar sol...

  4. CT-discography; diagnostic accuracy in lumbar disc herniation and significance of induced pain during procedure

    Energy Technology Data Exchange (ETDEWEB)

    Jin, En Hao [Yan Bian Medical College, Beijing (China); Chung, Tae Sub; Jeong, Mi Gyoung; Kim, Young Soo; Roh, Sung Woo [Yonsei Univ. College of Medicine, Seoul (Korea, Republic of)

    1996-01-01

    To evaluate the usefulness and the accuracy of CT-discography in lumbar disc disease by analyzing the findings of CT-discogram and types of evoked pain during the procedure. CT-discograms were retrospectively evaluated in 47 intervertebral discs of 20 patients with multilevel involvement of lumbar disc diseases. In 28 herniated discs confirmed at surgery, the findings of CT-discogram (28 disc levels/20 patients), MRI(23/16) and CT(21/15) were comparatively analysed. The type of pain after infusion of contrast media during CT-discography was compared with that prior to the procedure. The accuracy for determining types of the herniated lumbar disc when compared with post-operative results was 96.4%(27 discs/28 discs) in the CT-discogram, 82.6%(19 discs/23 discs) in MRI and 71.4%(15 discs/21 discs) in the CT scan. Pains encountered during discography were radiating pain in 12 discs and back pain in 24 discs. CT-discography was especially helpful in 10 patients with multilevel involvement of the lumbar disc diseases to evaluate the exact location of diseased disc(s) that provoked the pain. CT-discography is a highly accurate method in diagnosis of the herniated lumbar intervertebral discs and is very useful in determining the precise location related to the development of pain in such cases.

  5. Gas Modelling in the Disc of HD 163296

    Science.gov (United States)

    Tilling, I.; Woitke, P.; Meeus, G.; Mora, A.; Montesinos, B.; Riviere-Marichalar, P.; Eiroa, C.; Thi, W. -F.; Isella, A.; Roberge, A.; hide

    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

  6. Structure of radiation-dominated gravitoturbulent quasar discs

    Science.gov (United States)

    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.

  7. On the possibility of a warped disc origin of the inclined stellar discs at the Galactic Centre

    CERN Document Server

    Ulubay-Siddiki, A; Gerhard, O

    2012-01-01

    (Abridged) The Galactic Center (GC) hosts a population of young stars some of which seem to form mutually inclined discs of clockwise and counter clockwise rotating stars. We present a warped disc origin scenario for these stars assuming that an initially flat accretion disc becomes warped due to the Pringle instability, or due to Bardeen-Petterson effect, before it fragments to stars. We show that this is plausible if the star formation efficiency $\\epsilon_{SF} \\lesssim 1$, and the viscosity parameter $\\alpha \\sim 0.1$. After fragmentation, we model the disc as a collection of concentric, circular, mutually tilted rings, and construct warped disc models for mass ratios and other parameters relevant to the GC environment, but also for more massive discs. We take into account the disc's self-gravity and the torques exerted by a surrounding star cluster. We show that a self-gravitating low-mass disc ($M_d / M_{bh} \\sim 0.001$) precesses in integrity in the life-time of the stars, but precesses freely when the ...

  8. Radiation thermo-chemical models of protoplanetary discs. IV. Modelling CO ro-vibrational emission from Herbig Ae discs

    NARCIS (Netherlands)

    Thi, W. F.; Kamp, I.; Woitke, P.; van der Plas, G.; Bertelsen, R.; Wiesenfeld, L.

    2013-01-01

    Context. The carbon monoxide (CO) ro-vibrational emission from discs around Herbig Ae stars and T Tauri stars with strong ultraviolet emissions suggests that fluorescence pumping from the ground X1Σ+ to the electronic A1Π state of CO should be taken into account in disc models. Aims: We wish to unde

  9. Radiation thermo-chemical models of protoplanetary discs IV. Modelling CO ro-vibrational emission from Herbig Ae discs

    NARCIS (Netherlands)

    Thi, W. F.; Kamp, I.; Woitke, P.; van der Plas, G.; Bertelsen, R.; Wiesenfeld, L.

    2013-01-01

    Context. The carbon monoxide (CO) ro-vibrational emission from discs around Herbig Ae stars and T Tauri stars with strong ultraviolet emissions suggests that fluorescence pumping from the ground X-1 Sigma(+) to the electronic A(1)Pi state of CO should be taken into account in disc models. Aims. We w

  10. The presence and absence of lymphatic vessels in the adult human intervertebral disc: relation to disc pathology

    Energy Technology Data Exchange (ETDEWEB)

    Kliskey, Karolina; Williams, Kelly; Yu, J.; Urban, Jill; Athanasou, Nick [University of Oxford, Nuffield Department of Orthopaedic, Rheumatology and Musculoskeletal Science, Oxford (United Kingdom); Jackson, David [Weatherall Institute of Molecular Medicine, Human Immunology Unit, Oxford (United Kingdom)

    2009-12-15

    Although the normal adult human intervertebral disc is considered to be avascular, vascularised cellular fibrous tissue can be found in pathological conditions involving the disc such as disc herniation. Whether lymphatics vessels form a component of this reparative tissue is not known as the presence or absence of lymphatics in herniated and normal disc tissue is not known. We examined spinal tissues and discectomy specimens for the presence of lymphatics. The examination used immunohistochemistry to identify the specific lymphatic endothelial cell markers, podoplanin and LYVE1. Lymphatic vessels were not found in the nucleus pulposus or annulus fibrosus of intact, non-herniated lumbar and thoracic discs but were present in the surrounding ligaments. Ingrowth of fibrous tissue was seen in 73% of herniated disc specimens of which 36% contained LYVE1+/podoplanin + lymphatic vessels. Lymphatic vessels were not seen in the sacrum and coccyx or biopsies of four sacrococcygeal chordomas, but they were noted in surrounding extra-osseous fat and fibrous tissue at the edge of the infiltrating tumour. Our findings indicate that lymphatic vessels are not present in the normal adult intervertebral disc but that, when there is extrusion of disc material into surrounding soft tissue, there is ingrowth of reparative fibrous tissue containing lymphatic vessels. Our findings also indicate that chordoma, a tumour of notochordal origin, spreads to regional lymph nodes via lymphatics in para-spinal soft tissues. (orig.)

  11. Genetic Alterations in Intervertebral Disc Disease

    Directory of Open Access Journals (Sweden)

    Nikolay L. Martirosyan

    2016-11-01

    Full Text Available Background: Intervertebral disc degeneration (IVDD is considered a multifactorial disease. The last two decades of research strongly demonstrate that genetic factors contribute about 75% of the IVDD etiology. Recent total genome sequencing studies have shed light on the various single nucleotide polymorphisms (SNPs that are associated with IVDD.Aim: This review explores and presents updated information about the diversity of genetic factors in the inflammatory, degradative, homeostatic, and structural systems involved in the IVDD.Results: SNPs in the genes coding for structural proteins linked with IVDD or disc bulging include the Sp1 polymorphism of COL1A1, Trp3 polymorphism of COL9A3, several polymorphisms of COL11A1 and COL11A2, and a variable number tandem repeat polymorphism of ACAN. The rs4148941 SNP of CHST3 coding for an aggrecan sulfation enzyme is also associated with IVDD. The FokI, TaqI, and ApaI SNPs of the vitamin D receptor gene that is involved in chondrocyte functioning are also associated with IVDD. SNPs relevant to cytokine imbalance in IVDD include 889C/T of IL1a and 15T/A, as well as other SNPs (rs1800795, rs1800796, and rs1800797, of IL6, with effects limited to certain genders and populations. SNPs in collagenase genes include -1605G/D (guanine insertion/deletion of MMP1, -1306C/T of MMP2, -1562C/T and a 5-adenosine (5A variant (in the promotor region of MMP3, -1562C/T of MMP9, and -378T/C of MMP-14. SNPs in aggrecanase genes include 1877T/U of ADAMTS-4 and rs162509 of ADAMTS-5. Among the apoptosis-mediating genes, 1595T/C of the caspase 9 gene, 1525A/G and 1595T/C of the TRAIL gene, and 626C/G of the death receptor 4 gene (DR4 are SNPs associated with IVDD. Among the growth factors involved in disc homeostasis, the rs4871857 SNP of GDF5 was associated with IVDD. VEGF SNPs -2578C/A and -634G/C could foster neovascularization observed in IVDD.Conclusion: Improved understanding of the numerous genetic variants behind various

  12. Intraosseous disc prolapse: A diagnostic puzzle

    Directory of Open Access Journals (Sweden)

    Parasnis Rajesh

    2006-01-01

    Full Text Available Background : Schmorl′s node or intraosseous disc prolapse is herniation of the nucleus pulposus material through the vertebral end plates. Presence of Schmorl′s nodes as end plate lesions following trauma, tumours and osteoporosis further complicates diagnosis. The present study was done to understand diagnosis and approach to management of symptomatic Schmorl′s nodes. Methods : During a period of three years we came across 14 patients who presented with severe back pain. Conventional radiographs, CT Scans and MRI showed the presence of end plate lesions with varied radiological appearance. The first group, comprising of seven patients had lytic lesions without any sclerosis on only one side of the intervertebral disc as seen on the CT scan. The second group comprising of five patients had sclerotic lesions with new bone formation associated with disc space reduction. The two patients in the third group showed a combined lytic and sclerotic lesion without any soft tissue changes. MRI of eleven patients revealed hypointense lesion on T 1 and T 2 weighted images with surrounding zone of hyper intensity on T 2 weighted images. The remaining three patients, did not have this hyper intense zone on T 2 weighted images . In five patients multiple Schmorl′s nodes were observed. Diagnosis of symptomatic Schmorl′s nodes was mainly done by exclusion. All patients were given rest and anti-inflammatory drugs followed by exercises. Results : The first two groups of patients responded to the treatment and had complete relief of symptoms but both the patients in third group had persistent symptoms. MRI repeated after eight weeks showed an enhancing lesion with prevertebral soft tissue. A transpedicular core biopsy proved the lesion to be tuberculosis in one patient. Anti Koch′s therapy was promptly started and follow up study showed resolution of the lesions. At the end of the study period all the patients were asymptomatic and returned to their

  13. Numerical simulations of accretion discs: Pt. 1. Superhumps: a tidal phenomenon of accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Whitehurst, Robert

    1988-05-01

    Numerical simulations of the SU UMa star ZCha in outburst are presented which demonstrate the role of the secondary's tidal influence upon the accretion flow and provide explanations for the superhumps seen in SU UMa stars. They show that for a system with an extreme mass-ratio q = 0.15, the disc is tidally unstable and can become asymmetric and slowly rotate in the inertial frame of reference. The tidal stresses raised in this disc by the secondary produce a peak in the light curve of order 30 per cent which recurs with a period 3.5 per cent longer than that of the orbit. This is interpreted as the superhump. Analytic considerations show that only for systems with mass-ratios more extreme than approximately 4::1 will such behaviour occur, which is consistent with the known mass-ratio of SU UMa stars and other cataclysmic variables.

  14. Structure of magneto-Keplerian discs: an analytical solution for thin accretion discs threatened by stellar magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Kaburaki, O.

    1986-05-15

    The structure of Keplerian discs which are threaded by the magnetic field lines of each central star are considered. Under the assumptions of thin discs, stationarity and of axisymmetry, a fairly simple analytical solution is found. In such a disc, the electromagnetic force does not play any important role in the radial force balance, but it is this force that maintains the disc structure in the latitudinal direction. As suggested by previous authors, the angular momentum transfer is controlled by the global structure of the magnetic field. In contrast to their results, however, the present solution does not predict the switching of the azimuthal component of the magnetic field as a function of the radial distance in the disc.

  15. Preliminary study of disc hydrodynamic polishing.

    Science.gov (United States)

    Li, Yan; Lin, Bin; Zhang, XiaoFeng; Liu, PengFei

    2016-10-01

    In this paper, a developed polishing method based on elastic emission machining and Jules Verne-a variation on fluid jet polishing-is presented. This method is named disc hydrodynamic polishing (DHDP). A computational fluid dynamics (CFD)-based model that consists of a CFD model and an erosion model is introduced to predict the surface roughness obtained by DHDP. The performance of DHDP is studied by experiments. The slurry used in the experiments comprises 95% deionized water and 5% cerium oxide particles. Fused-silica glass is chosen as the workpiece. After the experiments, an ultrasmooth surface without cracks is obtained. The simulation results principally coincide with the experimental results. The experimental results show that the actual roughness is slightly less than the prediction and smaller particles are more favorable for obtaining a better surface roughness.

  16. Likelihood inference for unions of interacting discs

    DEFF Research Database (Denmark)

    Møller, Jesper; Helisová, Katarina

    is specified with respect to a given marked Poisson model (i.e. a Boolean model). We show how edge effects and other complications can be handled by considering a certain conditional likelihood. Our methodology is illustrated by analyzing Peter Diggle's heather dataset, where we discuss the results......To the best of our knowledge, this is the first paper which discusses likelihood inference or a random set using a germ-grain model, where the individual grains are unobservable edge effects occur, and other complications appear. We consider the case where the grains form a disc process modelled...... of simulation-based maximum likelihood inference and the effect of specifying different reference Poisson models....

  17. Development of Vibrating Disc Piezoelectric Gyroscope

    Directory of Open Access Journals (Sweden)

    A.K. Singh

    2004-07-01

    Full Text Available The paper presents an indigenously developed vibrating disc piezoelectric gyroscope, in which both excitation and detection have been done through piezoelectric, using PZT-5H material. The gyroscope has been driven to resonant state by direct piezoelectric effect, using 20 V ac signal at 93 kHz, and the output has been detected by the reverse piezoelectric effect.The performance of this gyroscope has been tested with 3 microprocessor-controlled turntable, and the output of the gyroscope has been found" to be linearly proportional to the rotationspeed within a range ± 150 °/s. The sensitivity of the gyroscope is about 0.5 mV/°/s, which is comparable to that of other gyroscopes of similar category

  18. Optic disc detection using ant colony optimization

    Science.gov (United States)

    Dias, Marcy A.; Monteiro, Fernando C.

    2012-09-01

    The retinal fundus images are used in the treatment and diagnosis of several eye diseases, such as diabetic retinopathy and glaucoma. This paper proposes a new method to detect the optic disc (OD) automatically, due to the fact that the knowledge of the OD location is essential to the automatic analysis of retinal images. Ant Colony Optimization (ACO) is an optimization algorithm inspired by the foraging behaviour of some ant species that has been applied in image processing for edge detection. Recently, the ACO was used in fundus images to detect edges, and therefore, to segment the OD and other anatomical retinal structures. We present an algorithm for the detection of OD in the retina which takes advantage of the Gabor wavelet transform, entropy and ACO algorithm. Forty images of the retina from DRIVE database were used to evaluate the performance of our method.

  19. GRINDING OF DOUBLE DISC GRINDING MACHINE

    Institute of Scientific and Technical Information of China (English)

    Hu Huiqing

    2005-01-01

    The grinding of two parallel sides of a component is accomplished with the accuracy and higher productivity by passing a blank through the truncated cone shape grinders, which are turned angles. The machine is designated by the name of double disc grinding machine (DDGM). Usually, it is used in the mass production. The relationship between these angles, the accuracy, productivity,allowance and parameters of the machine and technology is explained in detail by math, such as vector analysis, transformation of 3D space coordinates, etc. Therefore, in the aspects of qualitative and quantitative analyses, the grinding potential of DDGM is enormous increased and superior to conventional methods. Furthermore, the theoretical foundation of DDGM grinding design and technology is provided to improve, to expand and to create for future. The established machine design and practical experience of grinding technology will get great benefit by them.

  20. The Research of Artificial Cervical Disc Replacement

    Institute of Scientific and Technical Information of China (English)

    Zhao Zhua; Qiang Shenb

    2008-01-01

    Cervical arthroplasty after anterior decompression with insertion of a prosthetic total disc replacement has been suggested as an alternate to anterior cervical fusion. It develops quickly during recent years. Currently there are several cervical arthroplasty devices. Each device varies in terms of materials, range of motion and constraint. Early studies suggest that in the short term, the complication rate and efficacy is no worse than fusion surgery. Long-term results have not yet been reported. This review examines the current prostheses as well as discussing issues regarding indications and technique. It is hoped that an improvement of cervical arthroplasty occurs in terms of materials and design as spinal surgeons enter a new dines of the management of cervical spine disease.

  1. Role of discs large homolog 5

    Institute of Scientific and Technical Information of China (English)

    Frauke Friedrichs; Monika Stoll

    2006-01-01

    In 2004, an association of genetic variation in the discs large homolog 5 (DLG5) gene with inflammatory bowel disease (IBD) was described in two large European study samples[1]. The initial report of DLG5 as a novel IBD susceptibility gene sparked a multitude of studies investigating its effect on CD and IBD, respectively,leading to controversial findings and ongoing discussions concerning the validity of the initial association finding and its role in the aetiology of Crohn disease. This review aims to summarize the current state of knowledge and to place the reported findings in the context of current concepts of complex diseases. This includes aspects of statistical power, phenotype differences and genetic heterogeneity between different populations as well as gene-gene and gene-environment interactions.

  2. Disc instantons in linear sigma models

    Energy Technology Data Exchange (ETDEWEB)

    Govindarajan, Suresh E-mail: suresh@chaos.iitm.ernet.in; Jayaraman, T. E-mail: jayaram@imsc.ernet.in; Sarkar, Tapobrata E-mail: tapo@theory.tifr.res.in

    2002-12-16

    We construct a linear sigma model for open-strings ending on special Lagrangian cycles of a Calabi-Yau manifold. We illustrate the construction for the cases considered by Aganagic and Vafa (AV). This leads naturally to concrete models for the moduli space of open-string instantons. These instanton moduli spaces can be seen to be intimately related to certain auxiliary boundary toric varieties. By considering the relevant Gelfand-Kapranov-Zelevinsky (GKZ) differential equations of the boundary toric variety, we obtain the contributions to the world volume superpotential on the A-branes from open-string instantons. By using an ansatz due to Aganagic, Klemm and Vafa (AKV), we obtain the relevant change of variables from the linear sigma model to the non-linear sigma model variables--the open-string mirror map. Using this mirror map, we obtain results in agreement with those of AV and AKV for the counting of holomorphic disc instantons.

  3. Internal kinematics of modelled interacting disc galaxies

    CERN Document Server

    Kronberger, T; Schindler, S; Böhm, A; Kutdemir, E; Ziegler, B L

    2006-01-01

    We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows the procedure applied in observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys significantly disturb the velocity fields and hence the RCs of the interacting galaxies, leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are rising or falling profiles in direction to the companion galaxy and bumps in the RCs. In addition, tidal tails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshift galaxies, on which we focus our investigations. The appearance of these distortions depends, however, strongly on the viewing angle. The velocity ...

  4. Galactic disc warps due to intergalactic accretion flows onto the disc

    CERN Document Server

    López-Corredoira, M; Beckman, J E

    2007-01-01

    The accretion of the intergalactic medium onto the gaseous disc is used to explain the generation of galactic warps. A cup-shaped distortion is expected, due to the transmission of the linear momentum; but, this effect is small for most incident inflow angles and the predominant effect turns out to be the transmission of angular momentum, i.e. a torque giving an integral-sign shaped warp. The torque produced by a flow of velocity ~100 km/s and baryon density ~10^{-25} kg/m^3, which is within the possible values for the intergalactic medium, is enough to generate the observed warps and this mechanism offers quite a plausible explanation. The inferred rate of infall of matter, ~1 M_sun/yr, to the Galactic disc that this theory predicts agrees with the quantitative predictions of chemical evolution resolving key issues, notably the G-dwarf problem. Sanchez-Salcedo (2006) suggests that this mechanism is not plausible because it would produce a dependence of the scaleheight of the disc with the Galactocentric azim...

  5. New in vivo animal model to create intervertebral disc degeneration and to investigate the effects of therapeutic strategies to stimulate disc regeneration.

    Science.gov (United States)

    Kroeber, Markus W; Unglaub, Frank; Wang, Haili; Schmid, Carsten; Thomsen, Marc; Nerlich, Andreas; Richter, Wiltrud

    2002-12-01

    A new rabbit model was developed that produces disc degeneration through the application of controlled and quantified axial mechanical load. To characterize the changes associated with disc degeneration, and to evaluate the feasibility of local transfer of agents to the compressed discs to stimulate disc regeneration. Studies have shown that accelerated degeneration of the intervertebral disc results from altered mechanical loading conditions. The development of methods for the prevention of disc degeneration and the restoration of disc tissue that has already degenerated is needed. New Zealand white rabbits (n = 33) were used for this study. The discs in five animals remained unloaded and served as controls, whereas in 28 animals the discs were axially compressed using a custom-made external loading device. After 1 (n = 7), 14 (n = 7), and 28 (n = 7) days of dynamic loading, or 28 (n = 7) days of loading followed by 28 days of unloaded recovery time, the animals were killed and the lumbar spine was harvested for tissue preparation. Disc height, disc morphology, cell viability, disc stiffness, and load to failure were measured. Recombinant adenovirus encoding for two different marker genes (Ad-Luciferase and Ad-LacZ) was injected into the discs in loaded specimens and the gene expression was measured. The unloaded intervertebral discs of the rabbits consisted of a layered anulus fibrosus, a cartilaginous endplate, and a nucleus pulposus comparable with those of humans. After 14 and 28 days of loading, the discs demonstrated a significant decrease in disc space. Histologically, disorganization of the architecture of the anulus occurred. The number of dead cells increased significantly in the anulus and cartilage endplate. These changes were not reversible after 28 days of unloading. The stiffness and the load to failure did not change significantly in the discs after 28 days of loading, as compared with the unloaded control discs. Adenovirus-mediated gene transfer

  6. Percutaneous treatment of cervical and lumbar herniated disc

    Energy Technology Data Exchange (ETDEWEB)

    Kelekis, A., E-mail: akelekis@med.uoa.gr; Filippiadis, D.K., E-mail: dfilippiadis@yahoo.gr

    2015-05-15

    Therapeutic armamentarium for symptomatic intervertebral disc herniation includes conservative therapy, epidural infiltrations (interlaminar or trans-foraminal), percutaneous therapeutic techniques and surgical options. Percutaneous, therapeutic techniques are imaging-guided, minimally invasive treatments for intervertebral disc herniation which can be performed as outpatient procedures. They can be classified in 4 main categories: mechanical, thermal, chemical decompression and biomaterials implantation. Strict sterility measures are a prerequisite and should include extensive local sterility and antibiotic prophylaxis. Indications include the presence of a symptomatic, small to medium sized contained intervertebral disc herniation non-responding to a 4–6 weeks course of conservative therapy. Contraindications include sequestration, infection, segmental instability (spondylolisthesis), uncorrected coagulopathy or a patient unwilling to provide informed consent. Decompression techniques are feasible and reproducible, efficient (75–94% success rate) and safe (>0.5% mean complications rate) therapies for the treatment of symptomatic intervertebral disc herniation. Percutaneous, imaging guided, intervertebral disc therapeutic techniques can be proposed either as an initial treatment or as an attractive alternative prior to surgery for the therapy of symptomatic herniation in both cervical and lumbar spine. This article will describe the mechanism of action for different therapeutic techniques applied to intervertebral discs of cervical and lumbar spine, summarize the data concerning safety and effectiveness of these treatments, and provide a rational approach for the therapy of symptomatic intervertebral disc herniation in cervical and lumbar spine.

  7. Robust local intervertebral disc alignment for spinal MRI

    Science.gov (United States)

    Reisman, James; Höppner, Jan; Huang, Szu-Hao; Zhang, Li; Lai, Shang-Hong; Odry, Benjamin; Novak, Carol L.

    2006-03-01

    Magnetic resonance (MR) imaging is frequently used to diagnose abnormalities in the spinal intervertebral discs. Owing to the non-isotropic resolution of typical MR spinal scans, physicians prefer to align the scanner plane with the disc in order to maximize the diagnostic value and to facilitate comparison with prior and follow-up studies. Commonly a planning scan is acquired of the whole spine, followed by a diagnostic scan aligned with selected discs of interest. Manual determination of the optimal disc plane is tedious and prone to operator variation. A fast and accurate method to automatically determine the disc alignment can decrease examination time and increase the reliability of diagnosis. We present a validation study of an automatic spine alignment system for determining the orientation of intervertebral discs in MR studies. In order to measure the effectiveness of the automatic alignment system, we compared its performance with human observers. 12 MR spinal scans of adult spines were tested. Two observers independently indicated the intervertebral plane for each disc, and then repeated the procedure on another day, in order to determine the inter- and intra-observer variability associated with manual alignment. Results were also collected for the observers utilizing the automatic spine alignment system, in order to determine the method's consistency and its accuracy with respect to human observers. We found that the results from the automatic alignment system are comparable with the alignment determined by human observers, with the computer showing greater speed and consistency.

  8. Classification of the lumbar disc degeneration using MRI

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, Hirotoshi; Shinomiya, Kenichi; Okamoto, Akihiko; Muto, Naoko; Furuya, Kotaro (Tokyo Medical and Dental Univ. (Japan). School of Medicine)

    1992-11-01

    Magnetic resonance (MR) imaging has been performed in consecutive 114 patients with a chief complaint of lumbar pain. A retrospective review of MR images of a total of 570 lumbar vertebrae from these patients were done to examine lumbar disc degeneration. According to the MR intensity of nucleus pulposus on T2-wighted sagittal images, lumbar disc degeneration was graded on a scale of 0-4: 0=uniform hyperintensity; 1=slight hypointensity; 2=centrally band-like hypointensity with marginal hyperintensity; 3=irregular hypointensity in both the central and marginal sites; 4=uniform hypointensity. Lumbar disc degeneration was observed in 76%; and it was rapidly increased in frequency in the 30 or older age groups. Of 570 vertebrae, 51 (8.9%) had narrowing of intervertebral cavity. For these vertebrae, a mean score of lumbar disc degeneration was 3.1. Lumbar disc herniation was seen in 93 vertebrae, with a mean score of lumbar disc degeneration being 3.07. Changes in vertebral body marrow were seen in 14 vertebrae (2.5%), in which a mean score of intervertebral disc degeneration was 3.71. (N.K.).

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    Salmon, J; Canup, R M

    2014-09-13

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

  11. The evolution of self-gravitating accretion discs

    CERN Document Server

    Rice, Ken

    2016-01-01

    It is quite likely that self-gravity will play an important role in the evolution of accretion discs, in particular those around young stars, and those around supermassive black holes. We summarise, here, our current understanding of the evolution of such discs, focussing more on discs in young stellar system, than on discs in active galactic nuclei. We consider the conditions under which such discs may fragment to form bound objects, and when they might, instead, be expected to settle into a quasi-steady, self-regulated state. We also discuss how this understanding may depend on the mass of the disc relative to the mass of the central object, and how it might depend on the presence of external irradiation. Additionally, we consider whether or not fragmentation might be stochastic, where we might expect it to occur in an actual protostellar disc, and if there is any evidence for fragmentation actually playing a role in the formation of planetary-mass bodies. Although there are still a number of outstanding is...

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

    Science.gov (United States)

    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⊙.

  13. Self-gravity and the global structure of accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Abramowicz, M.A.; Curir, A.; Schwarzenberg-Czerny, A.; Wilson, R.E.

    1984-05-15

    We examine a number of issues related to the global structure of thick, self-gravitating, steady-state accretion discs, especially in regard to the effects of disc self-gravity on disc topology and disc dimensions. We begin by showing that inertial and viscous forces are negligible compared to gravitational, centrifugal and pressure gradient forces, provided that viscosity is sufficiently small, as would be expected. Two parameters of central importance are the relative disc mass (..mu..) and relative disc central density (xi). We use the Keplerian angular momentum, lsub(k), as the main variable in our descriptions of various physical effects, primarily because of its direct relation to the gravitational field and its relatively slow variation with distance. For computations of lsub(k) or gravitational potential we regard the disc mass distribution as that of a circular wire. Previous work has shown that this is an excellent first-order approximation. A sequence of figures illustrates all the physically different kinds of neutral points in the pressure gradient. Mass loss mechanisms involving these neutral points include the relativistic one expected near a central black hole, and a new non-relativistic one associated with configurations in which both ..mu.. and xi are not small. The consequences of the latter mechanism are discussed in some detail.

  14. The Disc-Jet Relation in Strong-Lined Blazars

    CERN Document Server

    D'Elia, V; Landt, H

    2003-01-01

    The relation between accretion disc (thermal emission) and jet (non-thermal emission) in blazars is still a mystery as, typically, the beamed jet emission swamps the disc even in the ultraviolet band where disc emission peaks. In this paper we estimate the accretion disc component for 136 flat-spectrum radio quasars selected from the Deep X-ray Radio Blazar Survey. We do this by deriving the accretion disc spectrum from the mass and accretion rate onto the central black hole for each object, estimated using the emission line widths and the power emitted from the broad line region. We find that non-thermal emission dominates the optical/UV band of our sources. The thermal component, in fact, is, on average, ~ 15 per cent of the total and > 90 per cent of the objects in the sample have a thermal component < 0.5 of the total luminosity. We then estimate the integrated disc and kinetic jet powers and find that, on average, the disc luminosity is ~ 1 to 20 times the jet power (depending on the uncertainties in ...

  15. Metallicity gradients of disc stars for a cosmologically simulated galaxy

    Science.gov (United States)

    Rahimi, Awat; Kawata, Daisuke; Allende Prieto, Carlos; Brook, Chris B.; Gibson, Brad K.; Kiessling, Alina

    2011-08-01

    We analyse for the first time the radial abundance gradients of the disc stars of a disc galaxy simulated with our three-dimensional, fully cosmological chemodynamical galaxy evolution code GCD+. We study how [Fe/H], [N/O], [O/Fe], [Mg/Fe] and [Si/Fe] vary with galactocentric radius. For the young stars of the disc, we found a negative slope for [Fe/H] and [N/O] but a positive [O/Fe], [Mg/Fe] and [Si/Fe] slope with radius. By analysing the star formation rate at different radii, we found that the simulated disc contains a greater fraction of young stars in the outer regions, while the old stars tend to be concentrated in the inner parts of the disc. This can explain the positive [α/Fe] gradient as well as the negative [N/O] gradient with radius. This radial trend is a natural outcome of an inside-out formation of the disc, regardless of its size and can thus explain the recently observed positive [α/Fe] gradients in the Milky Way disc open clusters.

  16. Metallicity gradients of disc stars for a cosmologically simulated galaxy

    CERN Document Server

    Rahimi, Awat; Prieto, Carlos Allende; Brook, Chris B; Gibson, Brad K; Kiessling, Alina

    2011-01-01

    We analyse for the first time the radial abundance gradients of the disc stars of a disc galaxy simulated with our three dimensional, fully cosmological chemodynamical galaxy evolution code GCD+. We study how [Fe/H], [N/O], [O/Fe], [Mg/Fe] and [Si/Fe] vary with galactocentric radius. For the young stars of the disc, we found a negative slope for [Fe/H] and [N/O] but a positive [O/Fe], [Mg/Fe] and [Si/Fe] slope with radius. By analysing the star formation rate (SFR) at different radii, we found that the simulated disc contains a greater fraction of young stars in the outer regions, while the old stars tend to be concentrated in the inner parts of the disc. This can explain the positive [alpha/Fe] gradient as well as the negative [N/O] gradient with radius. This radial trend is a natural outcome of an inside-out formation of the disc, regardless of its size and can thus explain the recently observed positive [alpha/Fe] gradients in the Milky Way disc open clusters.

  17. Accretion Discs with an Inner Spiral Density Wave

    CERN Document Server

    Montgomery, M M

    2010-01-01

    In Montgomery (2009a), we show that accretion discs in binary systems could retrogradely precess by tidal torques like the Moon and the Sun on a tilted, spinning, non-spherical Earth. In addition, we show that the state of matter and the geometrical shape of the celestial object could significantly affect the precessional value. For example, a Cataclysmic Variable (CV) Dwarf Novae (DN) non-magnetic system that shows negative superhumps in its light curve can be described by a retrogradely precessing, differentially rotating, tilted disc. Because the disc is a fluid and because the gas stream overflows the tilted disc and particles can migrate into inner disc annuli, coupled to the disc could be a retrogradely precessing inner ring that is located near the innermost annuli of the disc. However, numerical simulations by Bisikalo et al. (2003, 2004) and this work show that an inner spiral density wave can be generated instead of an inner ring. Therefore, we show that retrograde precession in non-magnetic, spinni...

  18. Can giant planets form by gravitational fragmentation of discs?

    CERN Document Server

    Stamatellos, Dimitris

    2007-01-01

    Context: Disc fragmentation has been proposed as a possible mechanism for the formation of giant planets at close distances to solar-type stars. However, it is debatable whether this mechanism can function in the inner region of real discs. Aims: To investigate the thermodynamics of discs and the probability of fragmentation. Methods: We use a newly developed method to treat the energy equation and equation of state, which accounts for radiative transfer effects in SPH simulations of protostellar discs. The different chemical and internal states of hydrogen and the properties of dust at different densities and temperatures (ice coated dust grains at low temperatures, ice melting, dust sublimation) are all taken into account by the new method. Results: We present radiative hydrodynamic simulations of discs where the effects of the equation of state and energy equation are taken into account. We focus on the inner parts of discs, R<40 AU and examine 2 cases (i) a disc heated by an ambient radiation field of ...

  19. On the formation of planetary systems in photoevaporating transition discs

    CERN Document Server

    Terquem, Caroline

    2016-01-01

    In protoplanetary discs, planetary cores must be at least 0.1 earth mass at 1 au for migration to be significant; this mass rises to 1 earth mass at 5 au. Planet formation models indicate that these cores form on million year timescales. We report here a study of the evolution of 0.1 earth mass and 1 earth mass cores, migrating from about 2 and 5 au respectively, in million year old photoevaporating discs. In such a disc, a gap opens up at around 2 au after a few million years. The inner region subsequently accrete onto the star on a smaller timescale. We find that, typically, the smallest cores form systems of non-resonant planets beyond 0.5 au with masses up to about 1.5 earth mass. In low mass discs, the same cores may evolve in situ. More massive cores form systems of a few earth masses planets. They migrate within the inner edge of the disc gap only in the most massive discs. Delivery of material to the inner parts of the disc ceases with opening of the gap. Interestingly, when the heavy cores do not mig...

  20. A photoevaporative gap in the closest planet-forming disc

    Science.gov (United States)

    Ercolano, Barbara; Rosotti, Giovanni P.; Picogna, Giovanni; Testi, Leonardo

    2017-01-01

    The dispersal of the circum-stellar discs of dust and gas surrounding young low-mass stars has important implications for the formation of planetary systems. Photoevaporation from energetic radiation from the central object is thought to drive the dispersal in the majority of discs, by creating a gap which disconnects the outer from the inner regions of the disc and then disperses the outer disc from the inside-out, while the inner disc keeps draining viscously on to the star. In this Letter, we show that the disc around TW Hya, the closest protoplanetary disc to Earth, may be the first object where a photoevaporative gap has been imaged around the time at which it is being created. Indeed, the detected gap in the Atacama large millimeter/submillimeter array images is consistent with the expectations of X-ray photoevaporation models, thus not requiring the presence of a planet. The photoevaporation model is also consistent with a broad range of properties of the TW Hya system, e.g. accretion rate and the location of the gap at the onset of dispersal. We show that the central, unresolved 870 μm continuum source might be produced by free-free emission from the gas and/or residual dust inside the gap.

  1. ROS: Crucial Intermediators in the Pathogenesis of Intervertebral Disc Degeneration

    Directory of Open Access Journals (Sweden)

    Chencheng Feng

    2017-01-01

    Full Text Available Excessive reactive oxygen species (ROS generation in degenerative intervertebral disc (IVD indicates the contribution of oxidative stress to IVD degeneration (IDD, giving a novel insight into the pathogenesis of IDD. ROS are crucial intermediators in the signaling network of disc cells. They regulate the matrix metabolism, proinflammatory phenotype, apoptosis, autophagy, and senescence of disc cells. Oxidative stress not only reinforces matrix degradation and inflammation, but also promotes the decrease in the number of viable and functional cells in the microenvironment of IVDs. Moreover, ROS modify matrix proteins in IVDs to cause oxidative damage of disc extracellular matrix, impairing the mechanical function of IVDs. Consequently, the progression of IDD is accelerated. Therefore, a therapeutic strategy targeting oxidative stress would provide a novel perspective for IDD treatment. Various antioxidants have been proposed as effective drugs for IDD treatment. Antioxidant supplementation suppresses ROS production in disc cells to promote the matrix synthesis of disc cells and to prevent disc cells from death and senescence in vitro. However, there is not enough in vivo evidence to support the efficiency of antioxidant supplementation to retard the process of IDD. Further investigations based on in vivo and clinical studies will be required to develop effective antioxidative therapies for IDD.

  2. Does the stellar disc flattening depend on the galaxy type?

    CERN Document Server

    Mosenkov, A V; Reshetnikov, V P; Bizyaev, D V; Kautsch, S J

    2015-01-01

    We analyze the dependence of the stellar disc flatness on the galaxy morphological type using 2D decomposition of galaxies from the reliable subsample of the Edge-on Galaxies in SDSS (EGIS) catalogue. Combining these data with the retrieved models of the edge-on galaxies from the Two Micron All Sky Survey (2MASS) and the Spitzer Survey of Stellar Structure in Galaxies (S$^4$G) catalogue, we make the following conclusions: (1) The disc relative thickness $z_0/h$ in the near- and mid-infrared passbands correlates weakly with morphological type and does not correlate with the bulge-to-total luminosity ratio $B/T$ in all studied bands. (2) Applying an 1D photometric profile analysis overestimates the disc thickness in galaxies with large bulges making an illusion of the relationship between the disc flattening and the ratio $B/T$. (3) In our sample the early-type disc galaxies (S0/a) have both flat and "puffed" discs. The early spirals and intermediate-type galaxies have a large scatter of the disc flatness, whic...

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

    Science.gov (United States)

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

    2016-05-01

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

  4. A biochemical/biophysical 3D FE intervertebral disc model.

    Science.gov (United States)

    Schroeder, Y; Huyghe, J M; van Donkelaar, C C; Ito, K

    2010-10-01

    Present research focuses on different strategies to preserve the degenerated disc. To assure long-term success of novel approaches, favorable mechanical conditions in the disc tissue are essential. To evaluate these, a model is required that can determine internal mechanical conditions which cannot be directly measured as a function of assessable biophysical characteristics. Therefore, the objective is to evaluate if constitutive and material laws acquired on isolated samples of nucleus and annulus tissue can be used directly in a whole-organ 3D FE model to describe intervertebral disc behavior. The 3D osmo-poro-visco-hyper-elastic disc (OVED) model describes disc behavior as a function of annulus and nucleus tissue biochemical composition, organization and specific constituent properties. The description of the 3D collagen network was enhanced to account for smaller fibril structures. Tissue mechanical behavior tests on isolated nucleus and annulus samples were simulated with models incorporating tissue composition to calculate the constituent parameter values. The obtained constitutive laws were incorporated into the whole-organ model. The overall behavior and disc properties of the model were corroborated against in vitro creep experiments of human L4/L5 discs. The OVED model simulated isolated tissue experiments on confined compression and uniaxial tensile test and whole-organ disc behavior. This was possible, provided that secondary fiber structures were accounted for. The fair agreement (radial bulge, axial creep deformation and intradiscal pressure) between model and experiment was obtained using constitutive properties that are the same for annulus and nucleus. Both tissue models differed in the 3D OVED model only by composition. The composition-based modeling presents the advantage of reducing the numbers of material parameters to a minimum and to use tissue composition directly as input. Hence, this approach provides the possibility to describe internal

  5. A viscous-convective instability in laminar Keplerian thin discs

    CERN Document Server

    Malanchev, Konstantin; Shakura, Nikolai

    2016-01-01

    Using the anelastic approximation of linearized hydrodynamic equations, we investigate the development of axially symmetric small perturbations in thin Keplerian discs. Dispersion relation is found as a solution of general Sturm-Liouville eigenvalue problem for different values of relevant physical parameters (viscosity, heat conductivity, disc semithickness). The analysis reveals the appearance of overstable mode for Prandtl parameter higher than some critical value. These modes have a viscous-convective nature and can serve as a seed for turbulence in astrophysical discs even in the absence of magnetic fields.

  6. Comparison of efficacy of three commercially available antibiotic discs

    Directory of Open Access Journals (Sweden)

    Joshi A

    2008-01-01

    Full Text Available A study was undertaken to evaluate the efficacy of commercially available antimicrobial discs manufactured by Oxoid, UK, HiMedia Laboratories, Mumbai and Span Diagnostics, Surat. The discs were evaluated for their performance on the basis of percentage of coefficient of variation (%CV which is a measure of reproducibility, mean zone diameters which is a measure of accuracy and range of zone diameter using both standard ATCC strains and clinical isolates. The data showed variation for all three manufacturers and therefore routine and regular quality control of discs as well as meticulous following of good laboratory practices is strongly advocated in clinical laboratories

  7. BSAC standardized disc susceptibility testing method (version 11).

    Science.gov (United States)

    Howe, R A; Andrews, J M

    2012-12-01

    This article highlights key amendments incorporated into version 11 of the BSAC standardized disc susceptibility testing method, available as Supplementary data at JAC Online (http://jac.oxfordjournals.org/) and on the BSAC web site (http://bsac.org.uk/susceptibility/guidelines-standardized-disc-susceptibility-testing-method/). The basic disc susceptibility testing method remains unchanged, but there have been a number of alterations to the interpretive criteria for certain organism/drug combinations due to continuing harmonization with the EUCAST MIC breakpoints and constant efforts to improve the reliability and clinical applicability of the guidance.

  8. Magnetic fields in giant planet formation and protoplanetary discs

    Science.gov (United States)

    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

  9. Microendoscopic discectomy for treatment of lumbar disc herniation

    Institute of Scientific and Technical Information of China (English)

    ARJUN Sinkemani; WU Xiao-tao

    2015-01-01

    A lumbar microendoscopic discectomy ( MED ) is a minimally invasive surgical technique performed through a tubular device which is designed for the pain relieve caused by herniated discs pressing the nerve roots . In 1997, a new minimally invasive surgical approach for the management of symptomatic lumbar disc herniation , MED was introduced .This technique uses a tubular retractor system and a microendoscope for visualization rather than the operating microscope .However , recent literature suggests that MED is an effective microendoscopic system which has a fine long-term outcome in treating lumbar disc herniation .This article describes the operative tech-niques and outcomes reported in the literature for MED .

  10. Quasi-periodic oscillations in luminous accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Okuda, T.; Mineshige, S. (Cambridge Univ. (UK). Inst. of Astronomy)

    1991-04-15

    We examine the time-dependent evolution of radial pulsational instabilities in luminous accretion discs around neutron stars, using a one-dimensional hydrodynamic code. In geometrically thin and optically thick accretion discs, radial oscillations are overstable to axisymmetric perturbations. It is due to a mechanism similar to the {epsilon} mechanism in stellar pulsation. We find that this instability induces large amplitude oscillations (more than 100 per cent) in accretion rates and small modulations (a few per cent) in temperature and surface in the inner part of the disc, both with local Keplerian frequencies. (author).

  11. Twisted accretion discs: the Bardeen-Petterson effect

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, S.; Pringle, J.E.

    1985-03-15

    The effects of Lense-Thirring precession on the inner regions of an accretion disc are calculated by solving the equations governing the tilt of a twisted, viscous disc derived by Papaloizou and Pringle (1983. Mon. Not. R. astr. Soc. 202, 1181). The earlier conclusion of previous authors that the rotation in the inner regions of the disc aligns with the spin of the hole is confirmed. It is found however, that previous estimates of the radius at which this alignment occurs are incorrect.

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

    Science.gov (United States)

    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.

  13. Debris Discs and Connection to Exoplanets: Herschel Overview

    Science.gov (United States)

    Greaves, J. S.

    2012-03-01

    Debris discs are an exciting science area that has been opened up by Herschel through deep far-infrared observations. Key Projects cover disc evolution from the early stages when planets form (GASPS) and onwards to discs hosted by stars even older than the Solar System (GT, DUNES, DEBRIS). New categories are being discovered, including very cold cometary belts and unusual types of dust grain, and new connections are being made for systems of low-mass stars and planets. I will review these discoveries in the context of our ideas on how planetesimal belts from and evolve.

  14. Magnetorotational instability in weakly ionised, stratified accretion discs

    CERN Document Server

    Salmeron, Roberto Aureliano; Salmeron, Raquel; Wardle, Mark

    2003-01-01

    The magnetorotational instability (MRI) (Balbus and Hawley 1991, Hawley and Balbus 1991) transports angular momentum radially outwards in accretion discs through the distortion of the magnetic field lines that connect fluid elements. In protostellar discs, low conductivity is important, especially in the inner regions (Gammie 1996, Wardle 1997). As a result, low k modes are relevant and vertical stratification is a key factor of the analysis. However, most models of the MRI in these environments have adopted either the ambipolar diffusion or resistive approximations and have not simultaneously treated stratification and Hall conductivity. We present here a linear analysis of the MRI, including the Hall effect, in a stratified disc.

  15. STUDY KOMPARASI LOST FOAM DAN KONVENSIONAL CASTING PRODUK DISC BRAKE

    OpenAIRE

    Yoso, Sumeru; -, Suyitno

    2014-01-01

    Disc brake component is a vital component with gray cast iron base material, it’s also fast lasting wearing part, so it has be replaced often. The disc brake replacement component in a local market is being supplied by the small scale local metal casting industries have the same quality as the genuine part.Disc brake making process is utilizing casting method inserting RCS core between drag and coup, than metal molten poured inside mold. The problem of this method is the product result often ...

  16. Effects of unisegmental disc compression on adjacent segments: an in vivo animal model.

    Science.gov (United States)

    Unglaub, Frank; Guehring, Thorsten; Lorenz, Helga; Carstens, Claus; Kroeber, Markus W

    2005-12-01

    It is controversial whether fusion of discs in the spine leads to increased degeneration on the remaining discs or whether the degenerative changes are merely a part of the inevitable natural history process. To determine the effects of unisegmental compression and subsequent recovery on adjacent segments, we studied histology, radiology and intradiscal pressure using an in vivo rabbit model. Fifteen New Zealand rabbits were divided in to three groups of five. In the first group, the intervertebral disc L4-L5 of the lumbar spine was axially loaded for 28 days with an external loading device. In the second group, the intervertebral disc was compressed for 28 days and allowed to recover for an equal amount of time, with the loading device removed. Five animals underwent a sham operation, in which the external loading device was situated, but their discs remained unloaded for 28 days. The intradiscal pressure was determined in the loaded discs as well as in the cranial and caudal adjacent discs. Lateral radiographs were taken from each subjected intervertebral disc with adjacent vertebral bodies and the cranial and caudal adjacent segments. The compressed discs showed lower intradiscal pressure in comparison with the control group, which remained unloaded. In the cranial and caudal discs adjacent to the loaded discs the average intradiscal pressure was similar to the unloaded controls. The loaded discs demonstrated a significant decrease in disc space. No discs adjacent to the loaded discs changed in height. The lamellar architecture of the inner, middle, and outer annulus became more disorganized in the loaded discs. The nucleus pulposus showed increase of mucoid degeneration and increased cell death. Intervertebral discs from the control group and the adjacent discs to the compressed discs maintained their normal morphology. This study shows that mechanical loading of discs in the spine can cause rapid degeneration. Adjacent discs, however, did not change in terms

  17. The Gaia-ESO Survey: the Galactic thick to thin disc transition

    NARCIS (Netherlands)

    Recio-Blanco, A.; de Laverny, P.; Kordopatis, G.; Helmi, A.; Hill, V.; Gilmore, G.; Wyse, R.; Adibekyan, V.; Randich, S.; Asplund, M.; Feltzing, S.; Jeffries, R.; Micela, G.; Vallenari, A.; Alfaro, E.; Allende Prieto, C.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Koposov, S. E.; Korn, A.; Lanzafame, A.; Pancino, E.; Smiljanic, R.; Jackson, R.; Lewis, J.; Magrini, L.; Morbidelli, L.; Prisinzano, L.; Sacco, G.; Worley, C. C.; Hourihane, A.; Bergemann, M.; Costado, M. T.; Heiter, U.; Joffre, P.; Lardo, C.; Lind, K.; Maiorca, E.

    2014-01-01

    Aims: The nature of the thick disc and its relation to the thin disc is presently an important subject of debate. In fact, the structural and chemo-dynamical transition between disc populations can be used as a test of the proposed models of Galactic disc formation and evolution. Methods: We used th

  18. 26 CFR 1.995-1 - Taxation of DISC income to shareholders.

    Science.gov (United States)

    2010-04-01

    ... 26 Internal Revenue 10 2010-04-01 2010-04-01 false Taxation of DISC income to shareholders. 1.995... income to shareholders. (a) In general. (1) Under § 1.991-1(a), a corporation which is a DISC for a... transfers to avoid tax. (2) Under section 995(a), the shareholders of a DISC, or a former DISC, are...

  19. A Dark Matter Disc in the Milky Way

    Science.gov (United States)

    Read, J. I.; Bruch, T.; Baudis, L.; Debattista, V. P.; Agertz, O.; Mayer, L.; Brooks, A. M.; Governato, F.; Peter, A. H. G.; Lake, G.

    2010-06-01

    Dark matter direct detection experiments need to know the local phase space density of dark matter fdm(r,v,t) in order to derive dark matter particle properties. To date, calculations for fdm(r,v,t) have been based on simulations that model the dark matter alone. Here we include the influence of the baryonic matter. We find that a star/gas disc at high redshift (z~1) causes merging satellites to be preferentially dragged towards the disc plane. This results in an accreted dark matter disc that contributes ~0.25-1 times the non-rotating halo density at the Solar position. We discuss the impact of the dark disc on dark matter direct detection experiments, and how we might be able to detect it in future Galactic surveys.

  20. Disc resonator gyroscope fabrication process requiring no bonding alignment

    Science.gov (United States)

    Shcheglov, Kirill V. (Inventor)

    2010-01-01

    A method of fabricating a resonant vibratory sensor, such as a disc resonator gyro. A silicon baseplate wafer for a disc resonator gyro is provided with one or more locating marks. The disc resonator gyro is fabricated by bonding a blank resonator wafer, such as an SOI wafer, to the fabricated baseplate, and fabricating the resonator structure according to a pattern based at least in part upon the location of the at least one locating mark of the fabricated baseplate. MEMS-based processing is used for the fabrication processing. In some embodiments, the locating mark is visualized using optical and/or infrared viewing methods. A disc resonator gyroscope manufactured according to these methods is described.

  1. Power diagrams and interaction processes for unions of discs

    DEFF Research Database (Denmark)

    Møller, Jesper; Helisova, Katarina

    We study a flexible class of finite disc process models with interaction between the discs. We let U denote the random set given by the union of discs, and use for the disc process an exponential family density with the canonical sufficient statistic only depending on geometric properties of U...... such as the area, perimeter, Euler-Poincar´e characteristic, and number of holes. This includes the quarmass-interaction process and the continuum random cluster model as special cases. Viewing our model as a connected component Markov point process, and thereby establish local and spatial Markov properties......, becomes useful for handling the problem of edge effects when only U is observed within a bounded observation window. The power tessellation and its dual graph become major tools when establishing inclusion-exclusion formulae, formulae for computing geometric characteristics of U, and stability properties...

  2. Power diagrams and interaction processes for unions of discs

    DEFF Research Database (Denmark)

    Møller, Jesper; Helisova, Katerina

    2008-01-01

     We study a flexible class of finite-disc process models with interaction between the discs. We let U denote the random set given by the union of discs, and use for the disc process an exponential family density with the canonical sufficient statistic depending only on geometric properties of U...... such as the area, perimeter, Euler-Poincaré characteristic, and the number of holes. This includes the quermass-interaction process and the continuum random-cluster model as special cases. Viewing our model as a connected component Markov point process, and thereby establishing local and spatial Markov properties......, becomes useful for handling the problem of edge effects when only U is observed within a bounded observation window. The power tessellation and its dual graph become major tools when establishing inclusion-exclusion formulae, formulae for computing geometric characteristics of U, and stability properties...

  3. Disc Motor: Conventional and Superconductor Simulated Results Analysis

    Science.gov (United States)

    Inácio, David; Martins, João; Neves, Mário Ventim; Álvarez, Alfredo; Rodrigues, Amadeu Leão

    Taking into consideration the development and integration of electrical machines with lower dimensions and higher performance, this paper presents the design and development of a three-phase axial flux disc motor, with 50 Hz frequency supply. It is made with two conventional semi-stators and a rotor, which can be implemented with a conventional aluminum disc or a high temperature-superconducting disc. The analysis of the motor characteristics is done with a 2D commercial finite elements package, being the modeling performed as a linear motor. The obtained results allow concluding that the superconductor motor provides a higher force than the conventional one. The conventional disc motor presents an asynchronous behavior, like a conventional induction motor, while the superconductor motor presents both synchronous and asynchronous behaviors.

  4. A disc in the heart of the Ant nebula

    CERN Document Server

    Lykou, Foteini; Lagadec, Eric; Zijlstra, Albert

    2007-01-01

    We present the discovery of a silicate disc at the centre of the planetary nebula Mz3 (the Ant). The nebula was observed with MIDI on the Very Large Telescope Interferometer (VLTI). The visibilities obtained at different orientations clearly indicate the presence of a dusty, nearly edge-on disc in the heart of the nebula. An amorphous silicate absorption feature is clearly seen in our mid-IR spectrum and visibility curves. We used radiative transfer Monte Carlo simulations to constrain the geometrical and physical parameters of the disc. We derive an inner radius of 9 AU (~6mas assuming D=1.4kpc). This disc is perpendicular to, but a factor of 10^{3} smaller than the optical bipolar outflow.

  5. Radiative transfer on decretion discs of Be binaries

    CERN Document Server

    Panoglou, Despina; Carciofi, Alex C; Okazaki, Atsuo T; Rivinius, Thomas

    2016-01-01

    In this work we explore the effect of binarity in the decretion disc of Be stars, in order to explain their variability. To this aim, we performed smoothed particle hydrodynamics (SPH) simulations on Be binary systems, following the matter ejected isotropically from the equator of the Be star towards the base of an isothermal decretion disc. We let the system evolve for time long enough to be considered at steady state, and focus on the effect of viscosity for coplanar prograde binary orbits. The disc structure is found to be locked to the orbital phase, exhibiting also a dependence on the azimuthal angle. Additionally, we present the first results from detailed non-local thermodynamic equilibrium (non-LTE) radiative transfer calculations of the disc structure computed with the SPH code. This is achieved by the use of the three-dimensional (3D) Monte Carlo code HDUST, which can produce predictions with respect to a series of observables.

  6. Adjacent Lumbar Disc Herniation after Lumbar Short Spinal Fusion

    Directory of Open Access Journals (Sweden)

    Koshi Ninomiya

    2014-01-01

    Full Text Available A 70-year-old outpatient presented with a chief complaint of sudden left leg motor weakness and sensory disturbance. He had undergone L4/5 posterior interbody fusion with L3–5 posterior fusions for spondylolisthesis 3 years prior, and the screws were removed 1 year later. He has been followed up for 3 years, and there had been no adjacent segment problems before this presentation. Lumbar magnetic resonance imaging (MRI showed a large L2/3 disc hernia descending to the L3/4 level. Compared to the initial MRI, this hernia occurred in an “intact” disc among multilevel severely degenerated discs. Right leg paresis and bladder dysfunction appeared a few days after admission. Microscopic lumbar disc herniotomy was performed. The right leg motor weakness improved just after the operation, but the moderate left leg motor weakness and difficulty in urination persisted.

  7. 26 CFR 1.992-1 - Requirements of a DISC.

    Science.gov (United States)

    2010-04-01

    ... income is income of a DISC to which the intercompany pricing rules authorized by section 994 apply. (b... or periods during which they held such stock within such taxable year. (h) Definition of “former...

  8. [Physical therapy for temporomandibular joint anterior disc displacement without reduction].

    Science.gov (United States)

    Cai, B

    2017-03-09

    Temporomandibular joint (TMJ) anterior disc displacement without reduction (ADDwoR) is a common type of temporomandibular joint disorders. Most patients experience limited mouth opening and joint pain at the same time. The standpoint of physical therapy is the function of the joint instead of the displaced disc. The treatment aims to make symptoms disappeared and joint function regained through 3M techniques, including modality, manual and movement. For ADDwoR patients with limited mouth opening within 2 month, manual therapy may reposition disc and the following splint and movement therapy can maintain disc-condyle relationship. Even so, restoring anatomical relationship is not the end of physical therapy. Enhanced health education and multidisciplinary cooperation are important for successful management of the ADDwoR patients.

  9. Product and process innovation of grey cast iron brake discs

    Energy Technology Data Exchange (ETDEWEB)

    Schorn, M. [Brembo S.P.A. (Italy)

    2006-07-01

    The brake disc out of grey cast iron often seems to be playing the role of the ''underdog'' in the technical examinations of the entire brake system. This is also reflected by the 25 year history of the {mu}-club. In a total of 93 presentations in those 25 years, only 3 were related to the topic of grey cast iron discs. This is not a correct relation to the importance of this component within the brake system. The disc, although per definition with a lower specific load than the pad, has the major task to store and dissipate the heat in which the kinetic energy of the vehicle is transformed. The disc also has a significant effect on NVH behaviour, particularly in the low frequency range. It also has a permanent fight with its weight as an unsprung mass. (orig.)

  10. Alignment in star-debris disc systems seen by Herschel

    CERN Document Server

    Greaves, J S; Thureau, N; Eiroa, C; Marshall, J P; Maldonado, J; Matthews, B C; Olofsson, G; Barlow, M J; Moro-Martin, A; Sibthorpe, B; Absil, O; Ardila, D R; Booth, M; Broekhoven-Fiene, H; Brown, D J A; Cameron, A Collier; del Burgo, C; Di Francesco, J; Duchene, G; Eisloffel, J; Ertel, S; Holland, W S; Horner, J; Kalas, P; Kavelaars, J J; Lestrade, J -F; Vican, L; Wilner, D J; Wolf, S; Wyatt, M C

    2013-01-01

    Many nearby main-sequence stars have been searched for debris using the far-infrared Herschel satellite, within the DEBRIS, DUNES and Guaranteed-Time Key Projects. We discuss here 11 stars of spectral types A to M where the stellar inclination is known and can be compared to that of the spatially-resolved dust belts. The discs are found to be well aligned with the stellar equators, as in the case of the Sun's Kuiper belt, and unlike many close-in planets seen in transit surveys. The ensemble of stars here can be fitted with a star-disc tilt of ~<10 degrees. These results suggest that proposed mechanisms for tilting the star or disc in fact operate rarely. A few systems also host imaged planets, whose orbits at tens of AU are aligned with the debris discs, contrary to what might be expected in models where external perturbers induce tilts.

  11. Mass transfer between debris discs during close stellar encounters

    CERN Document Server

    Jilkova, Lucie; Hammer, Michael; Zwart, Simon Portegies

    2016-01-01

    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 distributions in the space of orbital elements (semimajor axis, eccentricity, inclination, and argument of pericentre) around their new hos...

  12. The Evolution of Protoplanetary Discs in the Arches Cluster

    CERN Document Server

    Olczak, C; Harfst, S; Pfalzner, S; Zwart, S Portegies

    2012-01-01

    Most stars form in a cluster environment. These stars are initially surrounded by discs from which potentially planetary systems form. Of all cluster environments starburst clusters are probably the most hostile for planetary systems in our Galaxy. The intense stellar radiation and extreme density favour rapid destruction of circumstellar discs via photoevaporation and stellar encounters. Evolving a virialized model of the Arches cluster in the Galactic tidal field we investigate the effect of stellar encounters on circumstellar discs in a prototypical starburst cluster. Despite its proximity to the deep gravitational potential of the Galactic centre only a moderate fraction of members escapes to form an extended pair of tidal tails. Our simulations show that encounters destroy one third of the circumstellar discs in the cluster core within the first 2.5 Myr of evolution, preferentially affecting the least and most massive stars. A small fraction of these events causes rapid ejection and the formation of a we...

  13. WARPING AND PRECESSION IN EXTRAGALACTIC MASER ACCRETION DISCS

    Directory of Open Access Journals (Sweden)

    A. Caproni

    2009-01-01

    Full Text Available Interferometric maser observations have been used to probe the physical conditions of extragalactic accretion discs at sub-parsec scales. The inferred kinematic of the water maser spots presents small deviations from Keplerian motions, which have been attributed to the warping and twisting of the parsec-scale disc. However, their physical origin is still a matter of debate in the literature. Motivated by this, we analyzed the general relativistic Bardeen-Petterson e ect, driven by a Kerr black hole, as the potential physical mechanism responsible for the disc warping and precession in the nearby Seyfert 2 galaxies NGC 1068 and NGC 4258. Assuming a power-law accretion disc, whose parameters were constrained by the observational data, we derived the basic quantities concerning the Bardeen-Petterson e ect for both sources. Some consequences from this peculiar relativistic mechanism are also presented in this work.

  14. Alignment in star-debris disc systems seen by Herschel

    Science.gov (United States)

    Greaves, J. S.; Kennedy, G. M.; Thureau, N.; Eiroa, C.; Marshall, J. P.; Maldonado, J.; Matthews, B. C.; Olofsson, G.; Barlow, M. J.; Moro-Martín, A.; Sibthorpe, B.; Absil, O.; Ardila, D. R.; Booth, M.; Broekhoven-Fiene, H.; Brown, D. J. A.; Cameron, A. Collier; del Burgo, C.; Di Francesco, J.; Eislöffel, J.; Duchêne, G.; Ertel, S.; Holland, W. S.; Horner, J.; Kalas, P.; Kavelaars, J. J.; Lestrade, J.-F.; Vican, L.; Wilner, D. J.; Wolf, S.; Wyatt, M. C.

    2014-02-01

    Many nearby main-sequence stars have been searched for debris using the far-infrared Herschel satellite, within the DEBRIS, DUNES and Guaranteed-Time Key Projects. We discuss here 11 stars of spectral types A-M where the stellar inclination is known and can be compared to that of the spatially resolved dust belts. The discs are found to be well aligned with the stellar equators, as in the case of the Sun's Kuiper belt, and unlike many close-in planets seen in transit surveys. The ensemble of stars here can be fitted with a star-disc tilt of ≲ 10°. These results suggest that proposed mechanisms for tilting the star or disc in fact operate rarely. A few systems also host imaged planets, whose orbits at tens of au are aligned with the debris discs, contrary to what might be expected in models where external perturbers induce tilts.

  15. Goddard Earth Sciences Data and Information Services Center (GES DISC)

    Data.gov (United States)

    National Aeronautics and Space Administration — The NASA Goddard Earth Sciences (GES) Data and Information Services Center (DISC) is the home (archive) of Precipitation, Atmospheric Chemistry and Dynamics, and...

  16. Numerical Modeling of Disc Brake System in Frictional Contact

    Directory of Open Access Journals (Sweden)

    A. Belhocine

    2014-03-01

    Full Text Available Safety aspect in automotive engineering has been considered as a number one priority in development of new vehicle. Each single system has been studied and developed in order to meet safety requirement. Instead of having air bag, good suspension systems, good handling and safe cornering, there is one most critical system in the vehicle which is brake systems. The objective of this work is to investigate and analyse the temperature distribution of rotor disc during braking operation using ANSYS Multiphysics. The work uses the finite element analysis techniques to predict the temperature distribution on the full and ventilated brake disc and to identify the critical temperature of the rotor by holding account certain parameters such as; the material used, the geometric design of the disc and the mode of braking. The analysis also gives us, the heat flux distribution for the two discs.

  17. The Outflow-Disc Interaction in Young Stellar Objects

    CERN Document Server

    Pestalozzi, M R

    2000-01-01

    In this work the most spectacular phenomena occurring during the formation of a star are briefly reviewed: accretion through a rotating disc of matter and outflow through the poles of the new stellar object. Magnetic fields have been proposed to be principally responsible for the coexistence of these opposed mechanisms of accretion and outflowing. According to different models, the magnetic fields are either twisted or stretched by the accretion disc, allowing the formation of polar channels through which part of the accreting matter can escape. The high degree of coupling between the physical parameters describing the young stellar object (e.g. circular velocity of the disc and the central object, viscosity, strength and freezing of magnetic fields, etc.) makes detailed understanding of the interaction between accretion discs and outflows very difficult. The models presented here provide only a partial answer to this difficult problem.

  18. Crova's Disc: A Way to Make Sound Waves "Visible."

    Science.gov (United States)

    Hastings, R. B.

    1981-01-01

    Explained are the differences between and offered are examples of longitudinal and transverse sound waves. Described is the construction of the Crova's Disc, a device used in the teaching of the propagation and properties of sound waves. (DS)

  19. The effect of radiative feedback on disc fragmentation

    CERN Document Server

    Mercer, Anthony

    2016-01-01

    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 secondary objects formed; (ii) episodic feedback from secondary objects heats and stabilises 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 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, th...

  20. The structure of protoplanetary discs around evolving young stars

    CERN Document Server

    Bitsch, Bertram; Lambrechts, Michiel; Morbidelli, Alessandro

    2014-01-01

    The formation of planets with gaseous envelopes takes place in protoplanetary accretion discs on time-scales of several millions of 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 Nebular (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, as they can act as sweet spots for the formation of planetesimals via the streaming instability and affect the direction...

  1. NASA GES DISC Level 2 Aerosol Analysis and Visualization Services

    Science.gov (United States)

    Wei, Jennifer; Petrenko, Maksym; Ichoku, Charles; Yang, Wenli; Johnson, James; Zhao, Peisheng; Kempler, Steve

    2015-01-01

    Overview of NASA GES DISC Level 2 aerosol analysis and visualization services: DQViz (Data Quality Visualization)MAPSS (Multi-sensor Aerosol Products Sampling System), and MAPSS_Explorer (Multi-sensor Aerosol Products Sampling System Explorer).

  2. A truly Newtonian softening length for disc simulations

    CERN Document Server

    Huré, Jean-Marc

    2014-01-01

    The softened point mass model is commonly used in simulations of gaseous discs including self-gravity while the value of associated length \\lambda 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 \\lambda 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.

  3. Rotation of a ice disc during the melting on a solid plate

    CERN Document Server

    Dorbolo, S; Darbois-Texier, B

    2016-01-01

    Ice discs were released at the surface of a thermalized aluminium plate. The fusion of the ice creates a lubrication film between the ice disc and the plate. The disc becomes very mobile. The situation is isomorphe to the Leidenfrost effect reported for liquid droplet evaporating at the surface of a plate which temperature is over the boiling temperature of the liquid. For the ice discs, we observe that, while the ice discs were melting, they were rotating. The ice disc rotates starts rotating. The rotation speed increases with the temperature of the plate and with the load put on the ice disc. A model is proposed to explain the spontaneous rotation of the ice disc. We claim that the rotation is due to the viscous entrainment of the ice disc by the liquid that flows around the ice disc.

  4. LUMBOSACRAL TRANSITIONAL ANATOMY TYPES AND DISC DEGENERATIVE CHANGES

    Directory of Open Access Journals (Sweden)

    Chabukovska Radulovska Jasminka

    2014-07-01

    Full Text Available Background and purpose: The relationship between presence of lumbo sacral transitional vertebra (LSTV and disc degenerative changes is unclear. The aim of the study was to examine the relation between different types of LSTV and disc degenerative changes at the transitional and the adjacent cephalad segment. Material and methods: Sixty-three patients (mean age 51.48 ± 13.51 out of 200 adults with low back pain who performed MRI examination of the lumbo sacral spine, classified as positive for LSTV, were included in the study. Annular tears, disc degeneration according to Phirmann classification and disc herniations were evaluated and graded at transitional and adjacent cephalad level. Results: The severity of disc degeneration at the transitional level and the adjacent level correlated with the types of LSTV. Severe disc degenerative changes were most frequent in articulated connection LSTV types and incombined LSTV type at the transitional level and in osseus connection LSTV types at the adjacent cephalad level. These changes were more frequent in unilateral articulated connection LSTV subtype (64% vs 54%; and in unilateral osseus connection LSTV subtype (25% vs no patients at transitional level, and in bilateral osseus connection LSTV subtype (100% vs 50% at the level above. High prevalence of disc herniations was observed in articulated connection LSTV types as well as in unilateral osseus connection LSTV subtype at transitional and the adjacent cephalad level. At the transitional level higher prevalence of disc herniations was characteristic for unilateral articulated connection LSTV sub type (46%vs 41% and for unilateral osseus connection LSTV subtype (50% vs no patients. At the adjacent level higher prevalence of disc herniations was observed in bilateral articulated connection LSTV subtype (38% vs 27% and in bilateral osseus connection LSTV subtype (50% vs 25%. Conclusions: The compact osseus connection (osseus bridging vs articular

  5. Involvement of wound and climacteric ethylene in ripening avocado discs.

    Science.gov (United States)

    Starrett, D A; Laties, G G

    1991-10-01

    Avocado (Persea americana Mill. cv Hass) discs (3 mm thick) ripened in approximately 72 hours when maintained in a flow of moist air and resembled ripe fruit in texture and taste. Ethylene evolution by discs of early and midseason fruit was characterized by two distinct components, viz. wound ethylene, peaking at approximately 18 hours, and climacteric ethylene, rising to a peak at approximately 72 hours. A commensurate respiratory stimulation accompanied each ethylene peak. Aminoethoxyvinyl glycine (AVG) given consecutively, at once and at 24 hours following disc preparation, prevented wound and climacteric respiration peaks, virtually all ethylene production, and ripening. When AVG was administered for the first 24 hours only, respiratory stimulation and softening (ripening) were retarded by at least a day. When AVG was added solely after the first 24 hours, ripening proceeded as in untreated discs, although climacteric ethylene and respiration were diminished. Propylene given together with AVG led to ripening under all circumstances. 2,5-Norbornadiene given continuously stimulated wound ethylene production, and it inhibited climacteric ethylene evolution, the augmentation of ethylene-forming enzyme activity normally associated with climacteric ethylene, and ripening. 2,5-Norbornadiene given at 24 hours fully inhibited ripening. When intact fruit were pulsed with ethylene for 24 hours before discs were prepared therefrom, the respiration rate, ethylene-forming enzyme activity buildup, and rate of ethylene production were all subsequently enhanced. The evidence suggests that ethylene is involved in all phases of disc ripening. In this view, wound ethylene in discs accelerates events that normally take place over an extended period throughout the lag phase in intact fruit, and climacteric ethylene serves the same ripening function in discs and intact fruit alike.

  6. Prevalence of disc cupping in non-glaucomatous eyes

    Directory of Open Access Journals (Sweden)

    José Pablo Chiappe

    2015-02-01

    Full Text Available This study assessed optic disc size and cupping, using a commercially available ophthalmoscope, in order to show norms of these values for clinical practice. Subjects were office-workers referred from their respective workplaces for a routine medical examination, which included eye examination. The optic disc size was classified as small, medium or large, for having a diameter 1.5 times (respectively the diameter of the ophthalmoscope's selected light spot on the posterior pole. The cupping was classified as the ratio of the vertical cupping diameter and the vertical disc diameter on a relative decimal scale from 0.0 to 1.0.This study included 184 subjects with a mean age of 40.5 ± 9.5 years; 149 (81% were males. Their mean ocular pressure was 12.4 ± 1.5 mmHg (range 10-17 mmHg. There was a high correlation between optic disc sizes and cupping in the right and left eyes (Pearson Correlation r = 0.866, p < 0.001; therefore, for simplicity only the data for right eyes are presented. According to our definition, the optic discs in these eyes comprised 27 (14.7% small, 141 (76.6% medium and 16 (8.7% large. The small optic discs were rarely cupped, and the large optic discs were always cupped. Optic disc cupping greater than 0.7 was rarely found and should be suspect of glaucoma. Clinical doctors should be aware of this and refer those subjects with abnormal cupping to the specialist.

  7. Radiological analysis for thoracolumbar disc herniation in spinopelvic sagittal alignment

    OpenAIRE

    Wang, Tao; Ma, Lei; Yang, Da-Long; Wang, Hui; Zhang, Di; Zhang, Ying-Ze; Ding, Wen-Yuan

    2017-01-01

    Abstract A retrospective study aims to explore differences in spinopelvic sagittal alignment between thoracolumbar disc herniation (TLD) and lower lumbar disc herniation (LLD). A total of 185 patients included 26 with TLD and 129 with LLD and 30 asymptomatic volunteers in normal group (NG). Each individual took full spine X-ray to evaluate pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), thoracic kyphosis (TK), TK+LL+PI, TK/LL, and sacrum-femoral-pubic symphys...

  8. HEAT TRANSIENT TRANSFER ANALYSIS OF BRAKE DISC /PAD SYSTEM

    OpenAIRE

    Thuppal Vedanta, Srivatsan; Kora, Naga Vamsi Krishna

    2016-01-01

    Braking is mainly controlled by the engine. Friction between a pair of pads and a rotating disc converts the kinetic energy of the vehicle into heat. High temperatures can be reached in the system which can be detrimental for both, components and passenger safety. Numerical techniques help simulate load cases and compute the temperatures field in brake disc and brake pads. The present work implements a Finite Element (FE) toolbox in Matlab/Simulink able to simulate different braking manoeuvre...

  9. The formation of disc galaxies in a LCDM universe

    OpenAIRE

    Agertz, Oscar; Teyssier, Romain; Moore, Ben

    2010-01-01

    We study the formation of disc galaxies in a fully cosmological framework using adaptive mesh refinement simulations. We perform an extensive parameter study of the main subgrid processes that control how gas is converted into stars and the coupled effect of supernovae feedback. We argue that previous attempts to form disc galaxies have been unsuccessful because of the universal adoption of strong feedback combined with high star formation efficiencies. Unless extreme amounts of energy are in...

  10. Iliac artery pseudoaneurysm after lumbar disc hernia operation

    Directory of Open Access Journals (Sweden)

    Mehmet Atay

    2016-03-01

    Full Text Available Lumbar disc herniation surgery is usually performed through a posterior approach. Vascular injuries can be counted among the complications. 39 years old male patient had lower extremity pain which has started after lumbar disc herniation surgery and continued for a month. Iliac arterial pseudoaneurysm has been detected in computerized tomography. It was successfully treated with vascular surgery [Cukurova Med J 2016; 41(0.100: 5-7

  11. Massive thin accretion discs: Pt. 3; Comparison with the observations

    Energy Technology Data Exchange (ETDEWEB)

    Laor, A. (Tel Aviv Univ. (Israel). Wise Observatory)

    1990-10-01

    This paper presents a detailed comparison of theoretical thin accretion disc models with the spectra of 101 bright AGN. The models have been described previously; they take into account all relativistic effects and use an improved approximation for the local spectrum. The comparison is made by fitting the observation with a two-component model, a thin 'bare' accretion disc and an underlying power law. (author).

  12. Observational constraints on viscosity in AGN accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Siemiginowska, A.; Czerny, B. (N. Copernicus Astronomical Centre, Warsaw (Poland))

    1989-07-15

    The optical/UV/soft X-ray big bump can be modelled as thermal emission from an accretion disc. The observed UV variability in AGN spectra may be caused by accretion-disc instabilities, and can be used to constrain the viscosity. The comparison of thermal time-scales with the observed time-scales of variability in 10 Seyfert galaxies and 16 QSOs indicates values for the parameter {alpha} of the order of 0.01 for most cases. (author).

  13. Massive thin accretion discs: Pt. 1. Calculated spectra

    Energy Technology Data Exchange (ETDEWEB)

    Laor, Ari; Netzer, Hagai (Tel Aviv Univ. (Israel). Dept. of Physics and Astronomy; Tel Aviv Univ. (Israel). Wise Observatory)

    1989-06-01

    Detailed calculations are presented of the structure and the spectrum of massive, geometrically thin, 'bare' accretion discs. The calculations are for an {alpha}-disc, with various assumptions about the viscosity and full relativistic corrections. The radiative transfer equations are solved using the Eddington approximation for an atmosphere with a vertical temperature gradient. All significant sources of opacity, for T>10/sup 4/ K, are included, and all models are found to be optically thick throughout. (author).

  14. Black hole accretion discs and screened scalar hair

    CERN Document Server

    Davis, Anne-Christine; Jha, Rahul

    2016-01-01

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

  15. Black hole accretion discs and screened scalar hair

    Science.gov (United States)

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

    2016-10-01

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

  16. Accretion disc onto a static non-baryonic compact object

    OpenAIRE

    Torres, Diego F.

    2002-01-01

    We study the emissivity properties of a geometrically thin, optically thick, steady accretion disc about a static boson star. Starting from a numerical computation of the metric potentials and the rotational velocities of the particles in the vicinity of the compact object, we obtain the power per unit area, the temperature of the disc, and the spectrum of the emitted radiation. In order to see if different central objects could be actually distinguished, all these results are compared with t...

  17. Accretion-disc model spectra for dwarf-nova stars

    OpenAIRE

    Idan, Irit; Lasota, Jean-Pierre; Hameury, Jean-Marie; Shaviv, Giora

    2008-01-01

    Radiation from accretion discs in cataclysmic variable stars (CVs) provides fundamental information about the properties of these close binary systems and about the physics of accretion in general. The detailed diagnostics of accretion disc structure can be achieved by including in its description all the relevant heating and cooling physical mechanism, in particular the convective energy transport that, although dominant at temperatures less than about 10 000 K, is usually not taken into acc...

  18. Imaging the transient boundary layer on a free rotating disc.

    Science.gov (United States)

    Matijasević, Branimir; Guzović, Zvonimir; Martinis, Vinko

    2002-10-01

    This report presents a visual study of the transition process of the laminar boundary layer (BL) in a turbulent BL on a free rotating disc. The imaging is based on an experimental investigation that aimed to analyze the structure of the BL by relating it to the ratio between turbulent energy and vortex energy, the critical and the transient Reynolds numbers (Re), the vortex numbers and their dependence on Re, and on the distance from the rotating disc.

  19. Disc battery ingestion; a single event with different outcomes

    Directory of Open Access Journals (Sweden)

    E. Sindi

    2017-06-01

    Full Text Available Foreign body (FB ingestion is a common problem especially in children below the age of 5 years. This is fueled by their curiosity to explore their surroundings. The ingested foreign body finds its way out of the gastrointestinal tract without any serious consequences most of the time. On the other hand, disc battery ingestion has been reported to cause serious harm when ingested including death. We report two patients who had ingested disc batteries and their respective outcomes.

  20. Height of lumbar discs measured from radiographs compared with degeneration and height classified from MR images

    Energy Technology Data Exchange (ETDEWEB)

    Frobin, W.; Brinckmann, P. [Muenster Univ. (Germany). Inst. fuer Experimentelle Biomechanik; Kramer, M.; Hartwig, E. [Ulm Univ. (Germany). Sektion fuer Unfallchirurgische Forschung und Biomechanik

    2001-02-01

    The relation between height of lumbar discs (measured from lateral radiographic views) and disc degeneration (classified from MR images) deserves attention in view of the wide, often parallel or interchanged use of both methods. The time sequence of degenerative signs and decrease of disc height is controversial. To clarify the issue, this cross-sectional study documents the relation between disc degeneration and disc height in a selected cohort. Forty-three subjects were selected at random from a cohort examined for potential disc-related disease caused by long-term lifting and carrying. From each subject a lateral radiographic view of the lumbar spine as well as findings from an MR investigation of (in most cases) levels T12/L1 to L5/S1 were available; thus, n = 237 lumbar discs were available for measurement and classification. Disc height was measured from the radiographic views with a new protocol compensating for image distortion and permitting comparison with normal, age- and gender-appropriate disc height. Degeneration as well as disc height were classified twice from MR images by independent observers in a blinded fashion. Disc degeneration classified from MR images is not related to a measurable disc height loss in the first stage of degeneration, whereas progressive degeneration goes along with progressive loss of disc height, though with considerable interindividual variation. Loss of disc height classified from MR images is on average compatible with loss of disc height measured from radiographs. In individual discs, however, classification of height loss from MR images is imprecise. The first sign of disc degeneration (a moderate loss of nucleus signal) precedes disc height decrease. As degeneration progresses, disc height decreases. Disc height decrease and progress of degeneration, however, appear to be only loosely correlated. (orig.)

  1. Thermo-mechanical behaviour of heavy-duty disc brake systems

    OpenAIRE

    Chen, J. P.

    2001-01-01

    In heavy-duty disc brake systems, braking is a transient, non-linear and asymmetrical thermo-mechanical process. Surface cracking, rather than wear, is the major factor limiting the brake disc's life. The disc material (cast-iron), heat transfer boundary conditions and pad-disc frictional reactions are characteristically non-linear and asymmetrical during the friction process. Non-uniform deformation and surface cracks in brake discs result from the accumulation of excess...

  2. Magnetic flux stabilizing thin accretion discs

    Science.gov (United States)

    Sądowski, Aleksander

    2016-10-01

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

  3. Wakes of ram pressure stripped disc galaxies

    CERN Document Server

    Roediger, E; Hoeft, M

    2006-01-01

    Spiral galaxies that move through the intracluster medium lose a substantial amount of their gas discs due to ram pressure stripping. The recent observations of NGC 4388 by Oosterloo & van Gorkom 2005 reveal a tail of stripped gas of ~ 100 kpc behind the source galaxy. We present first 3D hydrodynamical simulations of the evolution of such ram pressure stripped tails. We find that if the ICM wind does not vary significantly over a period of a few 100 Myr, subsonic galaxies produce a tail with regular features similar to a von-Karman vortex street. In this case, the tail widens systematically by about 45 kpc per 100 kpc distance behind the source galaxy. The widening rate is independent of the galaxy's inclination for a large range of inclinations. For supersonic galaxies, the tail is more irregular than for subsonic ones. The tail observed for NGC 4388 is narrower than the tails in our simulations. Reasons for this difference may be additional physical processes such as heat conduction or viscosity. In ad...

  4. The edge of the young Galactic disc

    CERN Document Server

    Carraro, Giovanni; Costa, Edgardo; Perren, Gabriel; Mointinho, Andre'

    2010-01-01

    In this work we report and discuss the detection of two distant diffuse stellar groups in the third Galactic quadrant. They are composed of young stars, with spectral types ranging from late O to late B, and lie at galactocentric distances between 15 and 20 kpc. These groups are located in the area of two cataloged open clusters (VdB-Hagen~04 and Ruprecht~30), projected towards the Vela-Puppis constellations, and within the core of the Canis Major over-density. Their reddening and distance has been estimated analyzing their color-color and color-magnitude diagrams, derived from deep $UBV$ photometry. The existence of young star aggregates at such extreme distances from the Galactic center challenges the commonly accepted scenario in which the Galactic disc has a sharp cut-off at about 14 kpc from the Galactic center, and indicates that it extends to much greater distances (as also supported by recent detection of CO molecular complexes well beyond this distance). While the groups we find in the area of Ruprec...

  5. Propagation of the Gravo-Magneto Disc Instability

    CERN Document Server

    Martin, Rebecca G

    2013-01-01

    Discs that contain dead zones are subject to the Gravo-Magneto (GM) instability that arises when the turbulence shifts from gravitational to magnetic. We have previously described this instability through a local analysis at some radius in the disc in terms of a limit cycle. A disc may be locally unstable over a radial interval. In this paper, we consider how the local instability model can describe global disc outbursts. The outburst is triggered near the middle of the range of locally unstable radii. The sudden increase in turbulence within high surface density material causes a snow plough of density that propagates both inwards and outwards. All radii inside of the trigger radius become unstable, as well as locally unstable radii outside the trigger radius. In addition, a locally stable region outside of the trigger radius may also become unstable as the gravitational instability is enhanced by the snow plough. For the circumstellar disc model we consider, we find that a quarter of the disc mass is accret...

  6. Self-regulated gravitational accretion in protostellar discs

    CERN Document Server

    Vorobyov, E I

    2007-01-01

    We present a numerical model for the evolution of a protostellar disc that has formed self-consistently from the collapse of a molecular cloud core. The global evolution of the disc is followed for several million years after its formation. The capture of a wide range of spatial and temporal scales is made possible by use of the thin-disc approximation. We focus on the role of gravitational torques in transporting mass inward and angular momentum outward during different evolutionary phases of a protostellar disc with disc-to-star mass ratio of order 0.1. In the early phase, when the infall of matter from the surrounding envelope is substantial, mass is transported inward by the gravitational torques from spiral arms that are a manifestation of the envelope-induced gravitational instability in the disc. In the late phase, when the gas reservoir of the envelope is depleted, the distinct spiral structure is replaced by ongoing irregular nonaxisymmetric density perturbations. The amplitude of these density pertu...

  7. Gas modelling in the disc of HD 163296

    CERN Document Server

    Tilling, I; 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; Ménard, F; Mendigutía, I; Duchêne, 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 ~ 4 Myr, with evidence of a circumstellar disc extending out to ~ 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]63mic line and upper limits for several other far infrared lines. We complement this with continuum data and ground-based observations of the 12CO 3-2, 2-1 and 13CO 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, ...

  8. The disc origin of the Milky Way bulge

    CERN Document Server

    Di Matteo, P

    2016-01-01

    The Galactic bulge, that is the prominent out-of-plane over-density present in the inner few kiloparsecs of the Galaxy, is a complex structure, as the morphology, kinematics, chemistry and ages of its stars indicate. To understand the nature of its main components -- those at [Fe/H] >~ -1 dex -- it is necessary to make an inventory of the stellar populations of the Galactic disc(s), and of their borders : the chemistry of the disc at the solar vicinity, well known from detailed studies of stars over many years, is not representative of the whole disc. This finding, together with the recent revisions of the mass and sizes of the thin and thick discs, constitutes a major step in understanding the bulge complexity. N-body models of a boxy/peanut-shaped bulge formed from a thin disc through the intermediary of a bar have been successful in interpreting a number of global properties of the Galactic bulge, but they fail in reproducing the detailed chemo-kinematic relations satisfied by its components and their morp...

  9. [Differentiation of concomitant glaucomatous optic neuropathy in optic disc drusen].

    Science.gov (United States)

    Mamikonian, V R; Galoian, N S; Sheremet, N L; Kazarian, E E; Kharlap, S I; Shemeleva-Demir, O A; Tatevosian, A A; Andzhelova, D V; Eksarenko, O V

    2013-01-01

    Characteristics of ocular blood flow (OBF) in primary open-angle glaucoma (POAG) in eyes with optic disc drusen have been investigated. The study enrolled 21 patient (35 eyes) with optic disc drusen, of which 7 (8 eyes) were diagnosed with POAG. Besides the standard tests, the ophthalmological assessment included evaluation of OBF (flowmetry) and an individual normal range of intraocular pressure (IOP). The results showed that optic disc drusen are not associated with OBF changes. Concomitant POAG might be suspected in a patient with optic disc drusen whose OBF is significantly decreased and IOP is above the individual normal range. Differentiation of morphofunctional changes in chronic optic neuropathy, which might be due to either glaucomatous optic neuropathy or optic disc drusen, is complicated when actual IOP lies within the average normal range. Ocular blood flow evaluation by means of flowmetry with calculation of an individual normal range of IOP has been demonstrated as a highly effective predictor of concomitant POAG in patients with optic disc drusen.

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

    Directory of Open Access Journals (Sweden)

    S Capossela

    2014-04-01

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

  11. Comparative Frictional Analysis of Automobile Drum and Disc Brakes

    Directory of Open Access Journals (Sweden)

    H.P. Khairnar

    2016-03-01

    Full Text Available In the present work, a comparative frictional behaviour of drum brakes and disc brakes in automobiles has been investigated. The influential factors; contact force and friction radius were modeled for the estimation of the friction coefficient for drum as well as disc brakes. The effect of contact force and friction radius is studied with varying conditions of parameters; longitudinal force, caliper force and torque on piston side as well as non-piston side. The numerical results obtained have been compared with the similar obtained from virtual Matlab/Simulink models for drum and disc brakes. The results evidenced that friction radius predominantly affects brake pressure and thus the friction coefficient, also the increase in contact force resulted with decrease in friction coefficient both for drum and disc brakes. Further it has been found that disc brakes exhibit gradual decrease of friction coefficient due to the equitable distribution of braking effort while drum brake presents sudden variations in friction coefficient. It can be revealed that frictional behaviour of disc brake is more consistent than drum brake.

  12. Secular evolution of viscous and self-gravitating circumstellar discs

    CERN Document Server

    Vorobyov, E I

    2008-01-01

    We add the effect of turbulent viscosity via the \\alpha-prescription to models of the self-consistent formation and evolution of protostellar discs. Our models are non-axisymmetric and carried out using the thin-disc approximation. Self-gravity plays an important role in the early evolution of a disc, and the later evolution is determined by the relative importance of gravitational and viscous torques. In the absence of viscous torques, a protostellar disc evolves into a self-regulated state with disk-averaged Toomre parameter Q \\sim 1.5-2.0, non-axisymmetric structure diminishing with time, and maximum disc-to-star mass ratio \\xi = 0.14. We estimate an effective viscosity parameter \\alpha_eff associated with gravitational torques at the inner boundary of our simulation to be in the range 10^{-4}-10^{-3} during the late evolution. Addition of viscous torques with a low value \\alpha = 10^{-4} has little effect on the evolution, structure, and accretion properties of the disc, and the self-regulated state is la...

  13. Face-on accretion onto a protoplanetary disc

    CERN Document Server

    Wijnen, T P G; Pelupessy, F I; Zwart, S Portegies

    2016-01-01

    Globular clusters (GCs) are known to harbor multiple stellar populations. To explain these observations Bastian et al. suggested a scenario in which a second population is formed by the accretion of enriched material onto the low-mass stars in the initial GC population. The idea is that the low-mass, pre-main sequence stars sweep up gas expelled by the massive stars of the same generation into their protoplanetary disc as they move through the GC core. We perform simulations with 2 different smoothed particle hydrodynamics codes to investigate if a low-mass star surrounded by a protoplanetary disc can accrete the amount of enriched material required in this scenario. We focus on the gas loading rate onto the disc and star as well as on the lifetime of the disc. We find that the gas loading rate is a factor of 2 smaller than the geometric rate, because the effective cross section of the disc is smaller than its surface area. The loading rate is consistent for both codes, irrespective of resolution. The disc ga...

  14. Spectral variability in transonic discs around black holes

    CERN Document Server

    Zampieri, L; Szuszkiewicz, E

    2001-01-01

    Transonic discs with accretion rates relevant to intrinsically bright Galactic X-ray sources ($L\\approx 10^{38}$-$10^{39} {\\rm erg s}^{-1}$) exhibit a time dependent cyclic behaviour due to the onset of a thermal instability driven by radiation pressure. In this paper we calculate radiation spectra emitted from thermally-unstable discs to provide detailed theoretical predictions for observationally relevant quantities. The emergent spectrum has been obtained by solving self-consistently the vertical structure and radiative transfer in the disc atmosphere. We focus on four particular stages of the disc evolution, the maximal evacuation stage and three intermediate stages during the replenishment phase. The disc is found to undergo rather dramatic spectral changes during the evolution, emitting mainly in the 1-10 keV band during outburst and in the 0.1-1 keV band off-outburst. Local spectra, although different in shape from a blackbody at the disc effective temperature, may be characterized in terms of a harden...

  15. Stability of self-gravitating discs under irradiation

    CERN Document Server

    Rice, W K M; Mamatsashvili, G R; Lodato, G; Clarke, C J

    2011-01-01

    Self-gravity becomes competitive as an angular momentum transport process in accretion discs at large radii, where the temperature is low enough that external irradiation likely contributes to the thermal balance. Irradiation is known to weaken the strength of disc self-gravity, and can suppress it entirely if the disc is maintained above the threshold for linear instability. However, its impact on the susceptibility of the disc to fragmentation is less clear. We use two-dimensional numerical simulations to investigate the evolution of self-gravitating discs as a function of the local cooling time and strength of irradiation. In the regime where the disc does not fragment, we show that local thermal equilibrium continues to determine the stress - which can be represented as an effective viscous alpha - out to very long cooling times (at least 240 dynamical times). In this regime, the power spectrum of the perturbations is uniquely set by the effective viscous alpha and not by the cooling rate. Fragmentation o...

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

    Science.gov (United States)

    Capossela, S; Schläfli, P; Bertolo, A; Janner, T; Stadler, B M; Pötzel, T; Baur, M; Stoyanov, J V

    2014-04-04

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

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

    CERN Document Server

    Nayakshin, Sergei

    2011-01-01

    It has been recently proposed that giant protoplanets migrating inward 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 p...

  18. Global lopsided instability in a purely stellar galactic disc

    CERN Document Server

    Saha, K; Jog, C

    2007-01-01

    It is shown that pure exponential discs in spiral galaxies are capable of supporting slowly varying discrete global lopsided modes, which can explain the observed features of lopsidedness in the stellar discs. Using linearized fluid dynamical equations with the softened self-gravity and pressure of the perturbation as the collective effect, we derive self-consistently a quadratic eigenvalue equation for the lopsided perturbation in the galactic disc. On solving this, we find that the ground-state mode shows the observed characteristics of the lopsidedness in a galactic disc, namely the fractional Fourier amplitude A$_1$ increases smoothly with the radius. These lopsided patterns precess in the disc with a very slow pattern speed with no preferred sense of precession. We show that the lopsided modes in the stellar disc are long-lived because of a substantial reduction ($\\sim$ a factor of 10 compared to the local free precession rate) in the differential precession. The numerical solution of the equations shows...

  19. Angular momentum of disc galaxies with a lognormal density distribution

    CERN Document Server

    Marr, John Herbert

    2015-01-01

    Whilst most galaxy properties scale with galaxy mass, similar scaling relations for angular momentum are harder to demonstrate. A lognormal (LN) density distribution for disc mass provides a good overall fit to the observational data for disc rotation curves for a wide variety of galaxy types and luminosities. In this paper, the total angular momentum J and energy $\\vert{}$E$\\vert{}$ were computed for 38 disc galaxies from the published rotation curves and plotted against the derived disc masses, with best fit slopes of 1.683$\\pm{}$0.018 and 1.643$\\pm{}$0.038 respectively, using a theoretical model with a LN density profile. The derived mean disc spin parameter was $\\lambda{}$=0.423$\\pm{}$0.014. Using the rotation curve parameters V$_{max}$ and R$_{max}$ as surrogates for the virial velocity and radius, the virial mass estimator $M_{disc}\\propto{}R_{max}V_{max}^2$ was also generated, with a log-log slope of 1.024$\\pm{}$0.014 for the 38 galaxies, and a proportionality constant ${\\lambda{}}^*=1.47\\pm{}0.20\\time...

  20. Comparative experiments on the technological performance of disc filters

    Science.gov (United States)

    Liu, Guangrong; Jiang, Hua; Liao, Dongmei; Deng, Yingchun

    2017-06-01

    The filtration performance of JY disc filters was compared with that of Arkal disc filters when a parallel filtration system was designed under lab-scale devices. The comparisons of working and backwash performance were made for different filtration level. The experimental results showed that the two kinds of filters had similar process performance and effluent water quality under the same experimental condition. JY filter has higher filter performance index (FPI) than Arkal disc filters with the micron rating from 20 to 55μm discs, on the other hand, FPI value of JY filter has lower FPI than Arkal disc filters with the micron rating from 100 to 200μm discs. The removal rates of suspended solid(SS) for both filters vary in the range from 64% to 91.5%, moreover, the mean removal rate of SS for JY and Arkal filter was 78.2% and 79% respectively. The removal rates of turbidity were lower than 13% and the mean removal rate of turbidity was 7% for both filters. The critical backwash time and the critical backwash water loss for both filters were 5 seconds and 15 litres respectively.

  1. Momentum theory of Joukowsky actuator discs with swirl

    Science.gov (United States)

    van Kuik, Gijs A. M.

    2016-09-01

    Actuator disc theory is the basis for most rotor design methods, be it with many extensions and engineering rules added to make it a well-established method. However, the off-design condition of a very low rotational speed Ω of the disc is still a topic for scientific discussions. Several authors have presented solutions of the associated momentum theory for actuator discs with a constant circulation, the so-called Joukowsky discs, showing the efficiency Cp → ∞ for Ω → 0. The momentum balance is very sensitive to the choice of the vortex core radius δ as the pressure and velocity gradients become infinite for δ → 0. Viscous vortex cores do not show this singular behaviour so an inviscid core model is sought which removes the momentum balance sensitivity to singular flow. A vortex core with a constant δ does so. Applying this results in Cp → 0 for Ω → 0, instead of Cp → ∞. The Joukowsky actuator disc theory is confirmed by a very good match with the numerically obtained results. It gives higher Cp values than corresponding solutions for discs with a Goldstein-based wake circulation published in literature.

  2. The fraction of young eclipsing binaries that host discs

    CERN Document Server

    Meng, Zeyang; Bell, Cameron P M; Mamajek, Eric E; Scott, Erin L

    2014-01-01

    We search for systems hosting eclipsing discs using a complete sample of eclipsing binaries (EBs); those previously identified in the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). Within a subsample of 2,823 high-cadence, high-photometric precision and large eclipsing depth detached EBs previously identified in the Large Magellanic Cloud (LMC), we find that the skewness and kurtosis of the light curves magnitude distribution within the primary eclipse can distinguish EBs hosting a disc from those without. Two systems with previously identified eclipsing discs (OGLE-LMC-ECL-11893 and OGLE-LMC-ECL-17782) are identified with near zero skewness ($|S|<0.5$) and positive kurtosis. No additional eclipsing disc systems were found in the OGLE-III LMC, Small Magellanic Cloud (SMC) or Galactic Disc (GD) EB light curves. We estimate that the fraction of detached near main-sequence LMC EBs (which have a primary with an $I$-band magnitude brighter than $\\simeq 19\\,\\rm{mag}$) that host a disc is...

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

    CERN Document Server

    Lega, E; Bitsch, B; Crida, A; Szulagyi, J

    2015-01-01

    For the very first time we present 3D simulations of planets embedded in stellar irradiated discs. It is well known that thermal effects could reverse the direction of planetary migration from inwards to outwards, potentially saving planets in the inner, optically thick parts of the protoplanetary disc. When considering stellar irradiation in addition to viscous friction as a source of heating, the outer disc changes from a shadowed to a flared structure. Using a suited analytical formula it has been shown that in the flared part of the disc the migration is inwards; planets can migrate outwards only in shadowed regions of the disc, { because the radial gradient of entropy is stronger there}. In order to confirm this result numerically, we have computed the total torque acting on planets held on fixed orbits embedded in stellar irradiated 3D discs using the hydrodynamical code FARGOCA. We find qualitatively good agreement between the total torque obtained with numerical simulations and the one predicted by th...

  4. PATHOGENESIS OF OPTIC DISC EDEMA IN RAISED INTRACRANIAL PRESSURE

    Science.gov (United States)

    Hayreh, Sohan Singh

    2015-01-01

    Optic disc edema in raised intracranial pressure was first described in 1853. Ever since, there has been a plethora of controversial hypotheses to explain its pathogenesis. I have explored the subject comprehensively by doing basic, experimental and clinical studies. My objective was to investigate the fundamentals of the subject, to test the validity of the previous theories, and finally, based on all these studies, to find a logical explanation for the pathogenesis. My studies included the following issues pertinent to the pathogenesis of optic disc edema in raised intracranial pressure: the anatomy and blood supply of the optic nerve, the roles of the sheath of the optic nerve, of the centripetal flow of fluids along the optic nerve, of compression of the central retinal vein, and of acute intracranial hypertension and its associated effects. I found that, contrary to some previous claims, an acute rise of intracranial pressure was not quickly followed by production of optic disc edema. Then, in rhesus monkeys, I produced experimentally chronic intracranial hypertension by slowly increasing in size space-occupying lesions, in different parts of the brain. Those produced raised cerebrospinal fluid pressure (CSFP) and optic disc edema, identical to those seen in patients with elevated CSFP. Having achieved that, I investigated various aspects of optic disc edema by ophthalmoscopy, stereoscopic color fundus photography and fluorescein fundus angiography, and light microscopic, electron microscopic, horseradish peroxidase and axoplasmic transport studies, and evaluated the effect of opening the sheath of the optic nerve on the optic disc edema. This latter study showed that opening the sheath resulted in resolution of optic disc edema on the side of the sheath fenestration, in spite of high intracranial CSFP, proving that a rise of CSFP in the sheath was the essential pre-requisite for the development of optic disc edema. I also investigated optic disc edema with

  5. Glucosamine Supplementation Demonstrates a Negative Effect On Intervertebral Disc Matrix in an Animal Model of Disc Degeneration

    Science.gov (United States)

    Jacobs, Lloydine; Vo, Nam; Coehlo, J. Paulo; Dong, Qing; Bechara, Bernard; Woods, Barrett; Hempen, Eric; Hartman, Robert; Preuss, Harry; Balk, Judith; Kang, James; Sowa, Gwendolyn

    2013-01-01

    Study Design Laboratory based controlled in vivo study Objective To determine the in vivo effects of oral glucosamine sulfate on intervertebral disc degeneration Summary of Background Data Although glucosamine has demonstrated beneficial effect in articular cartilage, clinical benefit is uncertain. A CDC report from 2009 reported that many patients are using glucosamine supplementation for low back pain (LBP), without significant evidence to support its use. Because disc degeneration is a major contributor of LBP, we explored the effects of glucosamine on disc matrix homeostasis in an animal model of disc degeneration. Methods Eighteen skeletally mature New Zealand White rabbits were divided into four groups: control, annular puncture, glucosamine, and annular puncture+glucosamine. Glucosamine treated rabbits received daily oral supplementation with 107mg/day (weight based equivalent to human 1500mg/day). Annular puncture surgery involved puncturing the annulus fibrosus (AF) of 3 lumbar discs with a 16G needle to induce degeneration. Serial MRIs were obtained at 0, 4, 8, 12, and 20 weeks. Discs were harvested at 20 weeks for determination of glycosaminoglycan(GAG) content, relative gene expression measured by RT-PCR, and histological analyses. Results The MRI index and NP area of injured discs of glucosamine treated animals with annular puncture was found to be lower than that of degenerated discs from rabbits not supplemented with glucosamine. Consistent with this, decreased glycosaminoglycan was demonstrated in glucosamine fed animals, as determined by both histological and GAG content. Gene expression was consistent with a detrimental effect on matrix. Conclusions These data demonstrate that the net effect on matrix in an animal model in vivo, as measured by gene expression, MRI, histology, and total proteoglycan is anti-anabolic. This raises concern over this commonly used supplement, and future research is needed to establish the clinical relevance of these

  6. Tuina Therapy for Prolapsed Lumbar Intervertebral Disc

    Institute of Scientific and Technical Information of China (English)

    ZHANG Bi-meng; WU Huan-gan; SHEN Jian; XIAO Yuan-chun

    2004-01-01

    Recurrent low back pain and reflex sciatica of lower limbs are the two leading symptoms of prolapsed lumbar intervertebral disc, which can be confirmed in the history, symptoms, signs and imaging examination such as CT scan and MRI. It should be differentiated from those conditions characterized by lumbago and/or possible sciatica. Tuina was performed mostly on the Bladder Meridian,Gallbladder Meridian and Governor Vessel, as well as their acupoints such as Jiaji (Ex-B 2) points,Shenshu (BL 23), Dachangshu (BL 25), Yaoyangguan (GV 3), Huantiao (GB 30), Weizhong (BL 40),Chengshan (BL 57), Yanglingquan (GB 34) and Ashi points. Thumb-massaging manipulation, rolling manipulation, pulling manipulation, pressing manipulation, kneading manipulation and grasping manipulation are often performed.%反复下腰痛和下肢反射性坐骨神经痛是腰椎间盘突出症的两大症状.根据病史、症状、体征以及影像学(包括CT、MRI等)结果,可以确诊.需与以腰痛为主要表现的疾病,以腰痛伴坐骨神经痛为主要表现的疾病和以坐骨神经痛为主要表现的疾病相鉴别.推拿保守治疗多以足太阳膀胱经、足少阳胆经及督脉为主,取相应的夹脊穴、肾俞、大肠俞、腰阳关、环跳、委中、承山、阳陵泉及阿是穴等以一指禅推法、滚法、扳法、按法、揉法和拿法等进行治疗.

  7. Epidural steroid injection for lumbar disc herniation in NFL athletes.

    Science.gov (United States)

    Krych, Aaron J; Richman, Daniel; Drakos, Mark; Weiss, Leigh; Barnes, Ronnie; Cammisa, Frank; Warren, Russell F

    2012-02-01

    To our knowledge, there is no published information on the efficacy of epidural steroid injections for the treatment of lumbar disc herniation in an athletic population. The purpose of this study was to evaluate the efficacy of epidural corticosteroid injection for treatment of lumbar disc herniation in a group of National Football League (NFL) players. We retrospectively reviewed the records of all NFL players who underwent an epidural steroid injection at our institution for incapacitating pain secondary to an acute lumbar disc herniation (confirmed on magnetic resonance imaging) from 2003 to 2010. Our primary outcome was success of the injection, defined as return to play. The secondary outcome of the study was to evaluate risk factors for failure of this treatment approach. Seventeen players had a total of 37 injections for 27 distinct lumbar disc herniation episodes from 2003 to 2010. The success rate of returning an athlete to play for a given episode of disc herniation was 89% (24 of 27 episodes) with an average loss of 2.8 practices (range = 0-12) and 0.6 games (range = 0-2) after the injection. Four players required a repeat injection for the same episode. Three of these four players ultimately failed conservative management and required surgical intervention. Risk factors for failing injection therapy included sequestration of the disc herniation on magnetic resonance imaging (P = 0.01) and weakness on physical examination (P = 0.002). There were no complications reported. In this highly selective group of professional athletes, our results suggest that epidural steroid injections are a safe and effective therapeutic option in the treatment of symptomatic lumbar disc herniation.

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

    Directory of Open Access Journals (Sweden)

    Pasi J Eskola

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

  9. Efficiency of thin magnetically arrested discs around black holes

    Science.gov (United States)

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

    2016-10-01

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

  10. Validated finite element analysis of the maverick total disc prosthesis.

    Science.gov (United States)

    Le Huec, Jean-Charles; Lafage, Virginie; Bonnet, Xavier; Lavaste, François; Josse, Loic; Liu, Minglyan; Skalli, Wafa

    2010-06-01

    Combining in vitro tests and finite element analysis to provide a more complete picture of the role that a disc prosthesis implant would play in the biomechanics of the spine. Analysis of the disc function after total disc prosthesis insertion with and without antero-posterior or lateral offset and in combination with adjacent fusion. To avoid the risk of degenerative cascade the total disc replacement may be considered as an alternative. Few finite element analysis combined with cadaver testing under loading conditions have been published today. In vitro tests were performed using 6 fresh human cadaver specimens to quantify the load-displacement behaviors before and after insertion of a total disc replacement (Maverick, Memphis) implant. A finite element (FE) spine model was validated with the data from the in vitro tests. This model is built on the basis of ANSYS software. The effect of the prosthesis positioning on the motion behavior at L4-L5 and on the inner loads over facets was evaluated in 4 configurations. The study showed that the motion behavior at the levels adjacent to the Maverick prosthesis remained the same as the intact spine, unlike a single level fusion at L5-S1. In the biomechanical study settings, Maverick prosthesis, once properly positioned, does not modify the motion behavior of the spine as compared with its intact state. The less-than-ideal positioning of the prosthesis, especially with anterior offset, affect significantly the range of motion of the spine segment and cause increase of inner load in the facets. Those results indicated a good reliability of the finite element model in representing both intact and instrumented spine segments. The in vitro test results demonstrated that Maverick disc prosthesis provides near physiologic function of a natural disc restores stability of the spine and preserves the segmental motion without undue stress on adjacent segments.To our knowledge, this study suggested for the first time the importance

  11. Clinical evaluation of disc battery ingestion in children.

    Science.gov (United States)

    Mirshemirani, AliReza; Khaleghnejad-Tabari, Ahmad; Kouranloo, Jaefar; Sadeghian, Naser; Rouzrokh, Mohsen; Roshanzamir, Fatolah; Razavi, Sajad; Sayary, Ali Akbar; Imanzadeh, Farid

    2012-04-01

    BACKGROUND The purpose of this study was to evaluate the characteristics, management, and outcomes of disc battery ingestion in children. METHODS We reviewed the medical records of children admitted to Mofid Children's Hospital due to disc battery ingestion from January 2006 to January 2010. Clear history, clinical symptoms and results of imaging studies revealed diagnosis of disc battery ingestion in suspected patients. The clinical data reviewed included age, gender, clinical manifestation, radiologic findings, location of disc battery, duration of ingestion, endoscopic results and surgical treatment. RESULTS We found 22 cases (11 males and 11 females) of disc battery ingestion with a mean age of 4.3 years (range: 9 months to 12 years). Common symptoms were vomiting, cough, dysphagia, and dyspnea. The mean duration of ingestion was 2.7 days (4 hours to 1.5 months). A total of 19 patients had histories of disc battery ingestion, but three cases referred with the above symptoms, and the batteries were accidentally found by x-ray. Only three cases had batteries impacted in the esophagus. Twelve batteries were removed endoscopically, 6 batteries spontaneously passed through the gastrointestinal (GI) tract within 5 to 7 days, and 4 patients underwent surgery due to complications: 3 due to tracheo-esophageal fistula (TEF) and 1 due to intestinal perforation. There was no mortality in our study. CONCLUSION Most cases of disc battery ingestion run uneventful courses, but some may be complicated. If the battery lodges in the esophagus, emergency endoscopic management is necessary. However, once in the stomach, it will usually pass through the GI tract.

  12. Disc fragmentation and the formation of Population III stars

    Science.gov (United States)

    Latif, M. A.; Schleicher, D. R. G.

    2015-05-01

    Our understanding of Population III star formation is still in its infancy. They are formed in dark matter minihaloes of 105-106 M⊙ at z = 20-30. Recent high-resolution cosmological simulations show that a protostellar disc forms as a consequence of gravitational collapse and fragments into multiple clumps. However, it is not entirely clear if these clumps will be able to survive to form multiple stars as simulations are unable to follow the disc evolution for longer times. In this study, we employ a simple analytical model to derive the properties of marginally stable steady-state discs. Our results show that the stability of the disc depends on the critical value of the viscous parameter α. For αcrit = 1, the disc is stable for an accretion rate of ≤10-3 M⊙ yr-1 and becomes unstable at radii about ≥ 100 au in the presence of an accretion rate of 10-2 M⊙ yr-1. For 0.06 < αcrit < 1, the disc can be unstable for both accretion rates. The comparison of the migration and the Kelvin-Helmholtz time-scales shows that clumps are expected to migrate inwards before reaching the main sequence. Furthermore, in the presence of a massive central star, the clumps within the central 1 au will be tidally disrupted. We also find that UV feedback from the central star is unable to disrupt the disc, and that photoevaporation becomes important only once the accretion rate has dropped to 2 × 10-4 M⊙ yr-1. As a result, the central star may reach a mass of 100 M⊙ or even higher.

  13. Nonlinear transient and chaotic interactions in disc brake squeal

    Science.gov (United States)

    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.

  14. A self-similar solution for thermal disc winds

    Science.gov (United States)

    Clarke, C. J.; Alexander, R. D.

    2016-08-01

    We derive a self-similar description for the 2D streamline topology and flow structure of an axisymmetric, thermally driven wind originating from a disc in which the density is a power-law function of radius. Our scale-free solution is strictly only valid in the absence of gravity or centrifugal support; comparison with 2D hydrodynamic simulations of winds from Keplerian discs however demonstrates that the scale-free solution is a good approximation also in the outer regions of such discs, and can provide a reasonable description even for launch radii well within the gravitational radius of the flow. Although other authors have considered the flow properties along streamlines whose geometry has been specified in advance, this is the first isothermal calculation in which the flow geometry and variation of flow variables along streamlines is determined self-consistently. It is found that the flow trajectory is very sensitive to the power-law index of radial density variation in the disc: the steeper the density gradient, the stronger is the curvature of streamlines close to the flow base that is required in order to maintain momentum balance perpendicular to the flow. Steeper disc density profiles are also associated with more rapid acceleration, and a faster fall-off of density, with height above the disc plane. The derivation of a set of simple governing equations for the flow structure of thermal winds from the outer regions of power-law discs offers the possibility of deriving flow observables without having to resort to hydrodynamical simulation.

  15. Biomechanical analysis of the camelid cervical intervertebral disc

    Directory of Open Access Journals (Sweden)

    Dean K. Stolworthy

    2015-01-01

    Full Text Available Chronic low back pain (LBP is a prevalent global problem, which is often correlated with degenerative disc disease. The development and use of good, relevant animal models of the spine may improve treatment options for this condition. While no animal model is capable of reproducing the exact biology, anatomy, and biomechanics of the human spine, the quality of a particular animal model increases with the number of shared characteristics that are relevant to the human condition. The purpose of this study was to investigate the camelid (specifically, alpaca and llama cervical spine as a model of the human lumbar spine. Cervical spines were obtained from four alpacas and four llamas and individual segments were used for segmental flexibility/biomechanics and/or morphology/anatomy studies. Qualitative and quantitative data were compared for the alpaca and llama cervical spines, and human lumbar specimens in addition to other published large animal data. Results indicate that a camelid cervical intervertebral disc (IVD closely approximates the human lumbar disc with regard to size, spinal posture, and biomechanical flexibility. Specifically, compared with the human lumbar disc, the alpaca and llama cervical disc size are approximately 62%, 83%, and 75% with regard to area, depth, and width, respectively, and the disc flexibility is approximately 133%, 173%, and 254%, with regard to range of motion (ROM in axial-rotation, flexion-extension, and lateral-bending, respectively. These results, combined with the clinical report of disc degeneration in the llama lower cervical spine, suggest that the camelid cervical spine is potentially well suited for use as an animal model in biomechanical studies of the human lumbar spine.

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

    Science.gov (United States)

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

    2016-10-01

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

  17. Tidal Truncation of Inclined Circumstellar and Circumbinary Discs in Young Stellar Binaries

    CERN Document Server

    Miranda, Ryan

    2015-01-01

    Recent observations have shown that circumstellar and circumbinary discs in young stellar binaries are often misaligned with respect to the binary orbital plane. We analyze the tidal truncation of such misaligned discs due to torques applied to the disc at the Lindblad resonances from the tidal forcings of the binary. We consider eccentric binaries with arbitrary binary-disc inclination angles. We determine the dependence of the tidal forcing strengths on the binary parameters and show that they are complicated non-monotonic functions of eccentricity and inclination. We adopt a truncation criterion determined by the balance between resonant torque and viscous torque, and use it to calculate the outer radii of circumstellar discs and the inner radii of circumbinary discs. Misaligned circumstellar discs have systematically larger outer radii than aligned discs, and are likely to fill their Roche lobes if inclined by more than $45^\\circ - 90^\\circ$, depending on the binary mass ratio and disc viscosity parameter...

  18. Electromagnetic vs. Lense-Thirring alignment of black hole accretion discs

    CERN Document Server

    Polko, Peter

    2015-01-01

    Accretion discs and black holes (BHs) have angular momenta that are generally misaligned with respect to each other, which can lead to warps in the discs and bends in any jets produced. We consider a disc that is misaligned at large radii and torqued by Lense-Thirring (LT) precession and a Blandford-Znajek (BZ) jet torque. We consider a variety of disc states that include radiatively inefficient thick discs, radiatively efficient thin discs, and super-Eddington accretion discs. The magnetic field strength of the BZ jet is chosen as either from standard equipartition arguments or from magnetically arrested disc (MAD) simulations. We show that standard thin accretion discs can reach spin-disc alignment out to large radii long before LT would play a role, as caused by the slow infall time that gives even a weak BZ jet time to align the disc. We show that geometrically thick radiatively inefficient discs and super-Eddington discs in the MAD state reach disc-spin alignment near the black hole when density profiles...

  19. Clinical and magnetic resonance evaluation of the temporomandibular joint with rotational disc displacement

    Energy Technology Data Exchange (ETDEWEB)

    Chiba, Masatoshi; Sakurada, Motoyuki; Echigo, Seishi [Tohoku Univ., Sendai (Japan). School of Dentistry; Kumagai, Masahiro; Kochi, Shoko

    1998-03-01

    The most common direction of temporomandibular joint (TMJ) disc displacement is anterior. Anterior disc displacement is associated with lateral or medial disc displacement, termed rotational disc displacement (RDD). There have been few systematic studies of the clinical and magnetic resonance imaging (MRI) findings of TMJs with RDD. The aim of this study was to assess the prevalence of RDD and to evaluate the relations between the direction of disc displacement (anteromedial RDD, anterolateral RDD, and pure anterior disc displacement) and clinical findings, including joint pain, joint sound, and range of motion, as well as MRI findings, including disc shape, disc reduction, disc mobility, degree of disc displacement, bone changes of the condyle, and degree of condylar translation. The study was based on MRI of 529 TMJs in 409 patients with symptoms and signs of TMJ. Sagittal and coronal T1-weighted SE images (1.5 Tesla) were used. MRI showed anteromedial RDD in 96 joints (18.1%), anterolateral RDD in 64 joints (12.1%), and anterior disc displacement in 207 joints (39.1%). There were no statistical differences between anterolateral RDD, anteromedial RDD, and anterior disc displacement with regard to clinical findings. The incidence of reducible disc was higher in anterolateral RDD than in anteromedial RDD or anterior disc displacement. The incidence of bone changes was lower in anterolateral RDD than in anterior disc displacement. There were no significant differences between anteromedial RDD and anterior disc displacement with regard to MRI findings. In conclusion, anteromedial RDD may represent the same clinical entity as anterior disc displacement, but it remains unclear whether or not anterolateral RDD differs from anteromedial RDD or anterior disc displacement. (author)

  20. Electromagnetic versus Lense-Thirring alignment of black hole accretion discs

    Science.gov (United States)

    Polko, Peter; McKinney, Jonathan C.

    2017-01-01

    Accretion discs and black holes (BHs) have angular momenta that are generally misaligned, which can lead to warped discs and bends in any jets produced. We examine whether a disc that is misaligned at large radii can be aligned more efficiently by the torque of a Blandford-Znajek (BZ) jet than by Lense-Thirring (LT) precession. To obtain a strong result, we will assume that these torques maximally align the disc, rather than cause precession, or disc tearing. We consider several disc states that include radiatively inefficient thick discs, radiatively efficient thin discs, and super-Eddington accretion discs. The magnetic field strength of the BZ jet is chosen as either from standard equipartition arguments or from magnetically arrested disc (MAD) simulations. We show that standard thin accretion discs can reach spin-disc alignment out to large radii long before LT would play a role, due to the slow infall time that gives even a weak BZ jet time to align the disc. We show that geometrically thick radiatively inefficient discs and super-Eddington discs in the MAD state reach spin-disc alignment near the BH when density profiles are shallow as in magnetohydrodynamical simulations, while the BZ jet aligns discs with steep density profiles (as in advection-dominated accretion flows) out to larger radii. Our results imply that the BZ jet torque should affect the cosmological evolution of BH spin magnitude and direction, spin measurements in active galactic nuclei and X-ray binaries, and the interpretations for Event Horizon Telescope observations of discs or jets in strong-field gravity regimes.

  1. Face-on accretion onto a protoplanetary disc

    Science.gov (United States)

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

    2016-10-01

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

  2. MBM 12: young protoplanetary discs at high galactic latitude

    Science.gov (United States)

    Meeus, G.; Juhász, A.; Henning, Th.; Bouwman, J.; Chen, C.; Lawson, W.; Apai, D.; Pascucci, I.; Sicilia-Aguilar, A.

    2009-04-01

    We present Spitzer infrared observations to constrain disc and dust evolution in young T Tauri stars in MBM 12, a star-forming cloud at high latitude with an age of 2 Myr and a distance of 275 pc. The region contains 12 T Tauri systems, with primary spectral types between K3 and M6; 5 are weak-line and the rest classical T Tauri stars. We first use MIPS and literature photometry to compile spectral energy distributions for each of the 12 members in MBM 12, and derive their IR excesses. Of the 8 stars that are detected with MIPS (spectral types between K3 and M5), only 1 lacks an IR excess - the other 7 all have an IR excess that can be attributed to a disc. This means that in MBM 12, for the detected spectral types K3-M5, we have a very high disc fraction rate, about 90%. Furthermore, 3 of those 7 excess sources are candidate transitional discs. The four lowest-mass systems in the cloud, with spectral types of M5-M6, were undetected by Spitzer. Their upper limits indicate that they either have a transitional disc, or no disc at all. The IRS spectra are analysed with the newly developed two-layer temperature distribution (TLTD) spectral decomposition method. For the 7 T Tauri stars with a detected IR excess, we analyse their solid-state features to derive dust properties such as mass-averaged grain size, composition and crystallinity. The mass-averaged grain size we determine from the 10 micron feature has a wide range, between 0.4 and 6 μm. This grain size is much smaller in the longer-wavelength region: between 0.1 and 1.5 μm. We find that later-type objects have larger grain sizes, as was already shown by earlier studies. Furthermore, we find a wide range in mass fraction of the crystalline grains, between 3 and (at least) 30%, with no relation to the spectral type nor grain size. We do find a spatial gradient in the forsterite to enstatite range, with more enstatite present in the warmer regions. The fact that we see a radial dependence of the dust properties

  3. Silver nano fabrication using leaf disc of Passiflora foetida Linn

    Science.gov (United States)

    Lade, Bipin D.; Patil, Anita S.

    2017-06-01

    The main purpose of the experiment is to develop a greener low cost SNP fabrication steps using factories of secondary metabolites from Passiflora leaf extract. Here, the leaf extraction process is omitted, and instead a leaf disc was used for stable SNP fabricated by optimizing parameters such as a circular leaf disc of 2 cm (1, 2, 3, 4, 5) instead of leaf extract and grade of pH (7, 8, 9, 11). The SNP synthesis reaction is tried under room temperature, sun, UV and dark condition. The leaf disc preparation steps are also discussed in details. The SNP obtained using (1 mM: 100 ml AgNO3+ singular leaf disc: pH 9, 11) is applied against featured room temperature and sun condition. The UV spectroscopic analysis confirms that sun rays synthesized SNP yields stable nano particles. The FTIR analysis confirms a large number of functional groups such as alkanes, alkyne, amines, aliphatic amine, carboxylic acid; nitro-compound, alcohol, saturated aldehyde and phenols involved in reduction of silver salt to zero valent ions. The leaf disc mediated synthesis of silver nanoparticles, minimizes leaf extract preparation step and eligible for stable SNP synthesis. The methods sun and room temperature based nano particles synthesized within 10 min would be use certainly for antimicrobial activity.

  4. Hydrogen-loosing planets in transition discs around young protostars

    CERN Document Server

    Nayakshin, Sergei

    2013-01-01

    We point out that protoplanets created in the framework of the Tidal Downsizing (TD) theory for planet formation play a very important role for the evolution of accretion discs hosting them. Since all TD protoplanets are initially as massive as $\\sim 10$ Jupiter masses, they are able to open very deep gaps in their discs, and even completely isolate the inner disc flows from the outer ones. Furthermore, in contrast to other planet formation theories, TD protoplanets are mass donors for their protostars. One potentially observable signature of planets being devoured by their protostars are FU Ori like outbursts, and episodic protostar accretion more generally, as discussed by a number of authors recently. Here we explore another observational implication of TD hypothesis: dust poor inner accretion flows, which we believe may be relevant to some of the observed mm-bright transitional discs around protostars. In our model, a massive protoplanet interrupts the flow of the outer dust-rich disc on its protostar, an...

  5. MRI turbulence and thermal instability in accretion discs

    Science.gov (United States)

    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.

  6. NIHAO III: the constant disc gas mass conspiracy

    Science.gov (United States)

    Stinson, G. S.; Dutton, A. A.; Wang, L.; Macciò, A. V.; Herpich, J.; Bradford, J. D.; Quinn, T. R.; Wadsley, J.; Keller, B.

    2015-11-01

    We show that the cool gas masses of galactic discs reach a steady state that lasts many Gyr after their last major merger in cosmological hydrodynamic simulations. The mass of disc gas, Mgas, depends mostly upon a galaxy virial mass and halo's spin, and less upon stellar feedback. Haloes with low spin have high star formation efficiency and lower disc gas mass. Similarly, lower stellar feedback leads to more star formation so the gas mass ends up being nearly the same regardless of stellar feedback strength. Rather than regulating cool gas mass, stellar feedback regulates the mass of stars that forms. Even considering spin, the Mgas relation with halo mass, M200 only shows a factor of 3 scatter. The simulated Mgas-M200 relation shows a break at M200 = 2 × 1011 M⊙ that corresponds to an observed break in the Mgas-M⋆ relation. The galaxies that maintain constant disc masses share a common halo gas density profile shape in all the simulated galaxies. In their outer regions, the profiles are isothermal. Where the profile rises above n = 10-3 cm-3, the gas readily cools and the profile steepens. Inside the disc, rotation supports gas with a flatter density profile. Energy injection from stellar feedback provides pressure support to the halo gas to prevent runaway cooling flows. The constant gas mass makes simpler models for galaxy formation possible, either using a `bathtub' model for star formation rates or when modelling chemical evolution.

  7. A Symptomatic Spinal Extradural Arachnoid Cyst with Lumbar Disc Herniation

    Directory of Open Access Journals (Sweden)

    Yoshinori Kadono

    2015-01-01

    Full Text Available Spinal epidural arachnoid cyst (EAC is a rare, usually asymptomatic condition of unknown origin, which typically involves the lower thoracic spine. We report a case of posttraumatic symptomatic EAC with lumbar disc herniation. A 22-year-old man experienced back pain and sciatica after a traffic accident. Neurological examination revealed a right L5 radiculopathy. Magnetic resonance imaging demonstrated a cystic lesion at the L3 to L5 level and an L4-5 disc herniation; computed tomography myelography showed that the right L5 root was sandwiched between the cyst and the herniation. A dural defect was identified during surgery. The cyst was excised completely and the defect was repaired. A herniation was excised beside the dural sac. Histology showed that the cyst wall consisted of collagen and meningothelial cells. Postoperatively the symptoms resolved. Lumbar spinal EACs are rare; such cysts may arise from a congenital dural crack and grow gradually. The 6 cases of symptomatic lumbar EAC reported in the literature were not associated with disc herniation or trauma. In this case, the comorbid disc herniation was involved in symptom progression. Although many EACs are asymptomatic, comorbid spinal disorders such as disc herniation or trauma can result in symptom progression.

  8. Dynamical and chemical evolution of the thin disc

    CERN Document Server

    Just, Andreas

    2015-01-01

    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 alpha-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 d...

  9. Dust production in debris discs: constraints on the smallest grains

    CERN Document Server

    Thebault, Philippe

    2016-01-01

    The surface energy constraint puts a limit on the smallest fragment $s_{surf}$ that can be produced after a collision. Based on analytical considerations, this mechanism has been recently identified as been potentially able to prevent the production of small dust grains in debris discs and cut off their size distribution at sizes larger than the blow-out size. We numerically investigate the importance of this effect to find under which conditions it can leave a signature in the small-size end of a disc's particle size distribution (PSD). An important part of this work is to map out, in a disc at steady-state, what is the most likely collisional origin for micron-sized grains, in terms of the sizes of their collisional progenitors. We implement, for the first time, the surface energy constraint into a collisional evolution code. We consider a debris disc extending from 50 to 100AU and 2 different stellar types. We also consider two levels of stirring in the disc: dynamically "hot" (e=0.075) and "cold" (e=0.01)...

  10. The magnetorotational instability in debris-disc gas

    Science.gov (United States)

    Kral, Quentin; Latter, Henrik

    2016-09-01

    Debris discs are commonly swathed in gas, which can be observed in UV, in fine structure lines in FIR, and in resolved maps of CO emission. Carbon and oxygen are overabundant in such gas, but it is severely depleted in hydrogen. As a consequence, its ionization fraction is remarkably high, suggesting that magnetohydrodynamic (MHD) processes could be important. In particular, the gas may be subject to the magnetorotational instability (MRI), and indeed, recent modelling of β Pictoris requires an anomalous viscosity to explain the gas's observed radial structure. In this paper, we explore the possibility that the MRI is active in debris-disc gas and responsible for the observed mass transport. We find that non-ideal MHD and dust-gas interactions play a subdominant role, and that linear instability is viable at certain radii. However, owing to low gas densities, the outer parts of the disc could be stabilized by a weak ambient magnetic field, though it is difficult to constrain such a field. Even if the MRI is stabilized by too strong a field, a magnetocentrifugal wind may be launched in its place, and this could lead to equivalent (non-turbulent) transport. Numerical simulations of the vertically stratified MRI in conditions appropriate to the debris-disc gas should be able to determine the nature of the characteristic behaviour at different radii, and decide on the importance of the MRI (and MHD more generally) on the evolution of these discs.

  11. Bending instability in galactic discs. Advocacy of the linear theory

    CERN Document Server

    Rodionov, S A

    2013-01-01

    We demonstrate that in N-body simulations of isolated disc galaxies there is numerical vertical heating which slowly increases the vertical velocity dispersion and the disc thickness. Even for models with over a million particles in a disc, this heating can be significant. Such an effect is just the same as in numerical experiments by Sellwood (2013). We also show that in a stellar disc, outside a boxy/peanut bulge, if it presents, the saturation level of the bending instability is rather close to the value predicted by the linear theory. We pay attention to the fact that the bending instability develops and decays very fast, so it couldn't play any role in secular vertical heating. However the bending instability defines the minimal value of the ratio between the vertical and radial velocity dispersions $\\sigma_z / \\sigma_R \\approx 0.3$ (so indirectly the minimal thickness) which could have stellar discs in real galaxies. We demonstrate that observations confirm last statement.

  12. Structure and variability of dynamo driven accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Pudritz, R.E. (Cambridge Univ. (UK). Inst. of Astronomy); Fahlman, G.G. (British Columbia Univ., Vancouver (Canada). Dept. of Geophysics and Astronomy)

    1982-02-01

    A turbulent dynamo operating in an accretion disc around a black hole can produce fields strong enough so that the Maxwell stress due to the fluctuations dominates. In this dynamo driven limit, enormous localized fluctuations can be expected because the Kepler flow energy density is efficiently tapped. The detailed radial structure of this model is calculated, which for Cyg X-1, predicts a cool (Tsub(max) approximately < 10/sup 8/ K), dense, thin (z/sub 0//r approximately < 10/sup -2/), and optically thick disc. A mean field B approximately < 10/sup 8/ G can be generated. Fluctuations of order b approximately 10/sup 12/ G at the inner accretion disc radius (rsub(*) approximately 1), falling to b approximately 10/sup 10/ G at rsub(*) approximately 30, provide an explanation for the Cyg X-1 millisecond bursts and shot noise in terms of flares on the disc surface. This is established by means of model independent, scaled reconnection experiments. The optical variability of 3C 273 could be explained as arising from flares on an accretion disc around a 10/sup 9/ solar masses black hole, with flare fields of b approximately 10/sup 7/ G at rsub(*) approximately 1.

  13. Silicate features in Galactic and extragalactic post-AGB discs

    CERN Document Server

    Gielen, C; Van Winckel, H; Evans, T Lloyd; Woods, P M; Kemper, F; Marengo, M; Meixner, M; Sloan, G C; Tielens, A G G M

    2011-01-01

    Aims. In this paper we study the Spitzer and TIMMI2 infrared spectra of post-AGB disc sources, both in the Galaxy and the LMC. Using the observed infrared spectra we determine the mineralogy and dust parameters of the discs, and look for possible differences between the Galactic and extragalactic sources. Methods. Modelling the full spectral range observed allows us to determine the dust species present in the disc and different physical parameters such as grain sizes, dust abundance ratios, and the dust and continuum temperatures. Results. We find that all the discs are dominated by emission features of crystalline and amorphous silicate dust. Only a few sample sources show features due to CO2 gas or carbonaceous molecules such as PAHs and C60 fullerenes. Our analysis shows that dust grain processing in these discs is strong, resulting in large average grain sizes and a very high crystallinity fraction. However, we do not find any correlations between the derived dust parameters and properties of the central...

  14. Signs of a faint disc population at polluted white dwarfs

    CERN Document Server

    Bergfors, Carolina; Dufour, Patrick; Rocchetto, Marco

    2014-01-01

    Observations of atmospheric metals and dust discs around white dwarfs provide important clues to the fate of terrestrial planetary systems around intermediate mass stars. We present Spitzer IRAC observations of 15 metal polluted white dwarfs to investigate the occurrence and physical properties of circumstellar dust created by the disruption of planetary bodies. We find subtle infrared excess emission consistent with warm dust around KUV 15519+1730 and HS 2132+0941, and weaker excess around the DZ white dwarf G245-58, which, if real, makes it the coolest white dwarf known to exhibit a 3.6 micron excess and the first DZ star with a bright disc. All together our data corroborate a picture where 1) discs at metal-enriched white dwarfs are commonplace and most escape detection in the infrared (possibly as narrow rings), 2) the discs are long lived, having lifetimes on the order of 10^6 yr or longer, and 3) the frequency of bright, infrared detectable discs decreases with age, on a timescale of roughly 500 Myr, su...

  15. Infrared characterization of thermal gradients on disc brakes

    Science.gov (United States)

    Panier, Stephane; Dufrenoy, Philippe; Bremond, Pierre

    2003-04-01

    The heat generated in frictional organs like brakes and clutches induces thermal distortions which may lead to localized contact areas and hot spots developments. Hot spots are high thermal gradients on the rubbing surface. They count among the most dangerous phenomena in frictional organs leading to damage, early failure and unacceptable braking performances such as brake fade or undesirable low frequency vibrations called hot judder. In this paper, an experimental study of hot spots occurrence in railway disc brakes is reported on. The aim of this study was to better classify and to explain the thermal gradients appearance on the surface of the disc. Thermograph measurements with an infrared camera have been carried out on the rubbing surface of brake discs on a full-scale test bench. The infrared system was set to take temperature readings in snap shot mode precisely synchronized with the rotation of the disc. Very short integration time allows reducing drastically haziness of thermal images. Based on thermographs, a classification of hot-spots observed in disc brakes is proposed. A detailed investigation of the most damaging thermal gradients, called macroscopic hot spots (MHS) is given. From these experimental researches, a scenario of hot spots occurrence is suggested step by step. Thanks to infrared measurements at high frequency with high resolution, observations give new highlights on the conditions of hot spots appearance. Comparison of the experimental observations with the theoretical approaches is finally discussed.

  16. Transforaminal Approach in Thoracal Disc Pathologies: Transforaminal Microdiscectomy Technique

    Directory of Open Access Journals (Sweden)

    Sedat Dalbayrak

    2014-01-01

    Full Text Available Objective. Many surgical approaches have been defined and implemented in the last few decades for thoracic disc herniations. The endoscopic foraminal approach in foraminal, lateral, and far lateral disc hernias is a contemporary minimal invasive approach. This study was performed to show that the approach is possible using the microscope without an endoscope, and even the intervention on the discs within the spinal canal is possible by having access through the foramen. Methods. Forty-two cases with disc hernias in the medial of the pedicle were included in this study; surgeries were performed with transforaminal approach and microsurgically. Extraforaminal disc hernias were not included in the study. Access was made through the Kambin triangle, foramen was enlarged, and spinal canal was entered. Results. The procedure took 65 minutes in the average, and the mean bleeding amount was about 100cc. They were mobilized within the same day postoperatively. No complications were seen. Follow-up periods range between 5 and 84 months, and the mean follow-up period is 30.2 months. Conclusion. Transforaminal microdiscectomy is a method that can be performed in any clinic with standard spinal surgery equipment. It does not require additional equipment or high costs.

  17. Temporomandibular joint sounds and disc dislocations incidence after orotracheal intubation.

    Science.gov (United States)

    Rodrigues, Estela T; Suazo, Iván C; Guimarães, Antonio S

    2009-01-01

    The aim of this study was to analyze the temporomandibular joint (TMJ) disc displacement and articular sounds incidence after orotracheal intubation. A prospective cohort study was conducted in the Hospital Universitário do Oeste do Paraná (HUOP), in Cascavel, Brazil. 100 patients (aged 14-74 years, mean 44 years), 34 male and 66 female, in need of surgical procedure with orotracheal intubation were evaluated. The anterior disc displacement with reduction incidence and the nonclassifiable sounds incidence by the Research Diagnostic Criteria Axis I was evaluated in all patients after orotracheal intubation. The patients was evaluated one day before and until two days after the procedure. Eight percent present with anterior disc displacement with reduction and 10% presented nonclassifiable sounds after the orotracheal intubation. There was no correlation of any kind regarding gender related influence in the incidence of disc dislocations (P = 0.2591) and TMJ sounds (P = 0.487). Although anterior disc dislocations and TMJ sounds after anesthetic with orotracheal intubation presented a low incidence (8%-10%), it is recommended that the evaluation of TMJ signs and symptoms be done before the anesthetic procedure to take care with susceptible patients manipulation.

  18. NIHAO VI. The hidden discs of simulated galaxies

    CERN Document Server

    Obreja, A; Dutton, A A; Macciò, A V; Wang, L; Kang, X

    2016-01-01

    Detailed studies of galaxy formation require clear definitions of the structural components of galaxies. Precisely defined components also enable better comparisons between observations and simulations. We use a subsample of eighteen cosmological zoom-in simulations from the NIHAO project to derive a robust method for defining stellar kinematic discs in galaxies. Our method uses Gaussian Mixture Models in a 3D space of dynamical variables. The NIHAO galaxies have the right stellar mass for their halo mass, and their angular momenta and S\\'ersic indices match observations. While the photometric disc-to-total ratios are close to 1 for all the simulated galaxies, the kinematic ratios are around ~0.5. Thus, exponential structure does not imply a cold kinematic disc. Above log(M*)~9.5, the decomposition leads to thin discs and spheroids that have clearly different properties, in terms of angular momentum, rotational support, ellipticity, [Fe/H] and [O/Fe]. At log(M*)<9.5, the decomposition selects discs and sph...

  19. OVERLOAD STUDY ON ADJACENT DISC AFTER ARTHRODESIS IN THORACOLUMBAR FRACTURES

    Directory of Open Access Journals (Sweden)

    GUSTAVO SERRA REINAS

    Full Text Available ABSTRACT Objective: To analyze the degeneration of the adjacent disc after arthrodesis due to thoracolumbar fractures. Methods: Eighty-three patients who underwent posterolateral arthrodesis in thoracolumbar levels had their x-rays analyzed for degeneration of adjacent discs to the arthrodesis. The disc spaces were classified by the UCLA scale. Results: Of the 83 patients evaluated, 66 were males (79% and 18 females (21%, with a mean age of 35.5 years. The mean follow-up period was 40 months. As the fractures 75% were between T12 and L2 (p<0.001, being of the A3 type in 65% of the cases (p<0.001. The most common mechanism of injury, accounting for 50% of the cases (p<0.001, was fall from height. Only 6% of the superior discs and 12% of the inferior ones showed some degree of degeneration. No patient underwent a new surgical approach. Conclusion: The incidence of degeneration on adjacent disc in patients after arthrodesis resulting from fractures ranged from 6% to 12% with an average follow-up of 40 months.

  20. Anisotropic ion diffusivity in intervertebral disc: an electrical conductivity approach.

    Science.gov (United States)

    Jackson, Alicia; Yao, Hai; Brown, Mark D; Yong Gu, Wei

    2006-11-15

    Investigation of the transport behavior of ions in intervertebral disc using an electrical conductivity method. To determine the electrical conductivity and ion diffusivity of nucleus pulposus and anulus fibrosus in 3 major directions (axial, circumferential, and radial). Knowledge of diffusivity of small molecules is important for understanding nutrition supply in intervertebral disc and disc degeneration. However, little is known on the anisotropic behaviors of ion diffusivity and of electrical conductivity in intervertebral disc. Electrical conductivity measurement was performed on 24 axial, circumferential, and radial anulus fibrosus specimens and 24 axial nucleus pulposus specimens from bovine coccygeal discs. The diffusivity of Na and Cl were estimated by the analysis of conductivity data. The electrical conductivity (mean +/- standard deviation; n = 24) of the bovine anulus fibrosus was 4.70 +/- 1.08 mS/cm in the axial, 2.86 +/- 0.83 mS/cm in the radial, and 4.38 +/- 1.25 mS/cm in the circumferential direction. For nucleus pulposus, the electrical conductivity (mean +/- standard deviation; n = 24) was 8.95 +/- 0.89 mS/cm. The mean value for nucleus pulposus was significantly higher than that of anulus fibrosus (t test, P conductivity in the radial direction was significantly lower than in axial or circumferential directions. Similar trends were found for both Na and Cl diffusivities. Both electrical conductivity and ion diffusivity were highly sensitive to water content. Electrical conductivity and ion diffusivity of anulus fibrosus are anisotropic.